HP6255A Service Manual

A R M Y T M 1 1 - 6 1 3 0 - 4 1 6 - 1 4N A V Y EE010-BJ-MMA-010/E154 DCDUAL

A I R F O R C E T . O . 3 5 C 1 - 2 - 8 4 7 - 1

T E C H N I C A L M A N U A L

O P E R A T O R S , O R G A N I Z A T I O N A L ,D I R E C T S U P P O R T A N D G E N E R A L S U P P O R T

M A I N T E N A N C E M A N U A LF O R

P O W E R S U P P L Y , D U A L D C(H-P MODEL 6255A)

(NSN 6130-00-065-6811)

DEPARTMENTS OF THE ARMY, NAVY, AND AIR FORCE

31 JANUARY 1983

TM 11-6130-416-14/EE010-BJ-MMA-010/E154 DCDUAL/T.O.35C1-2-847-1

S A F E T Y S T E P S T O F O L L O W I F S O M E O N EIS THE VICTIM OF ELECTRICAL SHOCK

DO NOT TRY TO PULL OR GRAB THE lNDl -V I D U A L

IF POSSIBLE, TURN OFF THE ELECTRICALP O W E R

IF YOU CANNOT TURN OFF THE ELECTRICALPOWER, PULL, PUSH, OR L IFT THE PERSON TOSAFETY USING A WOODEN POLE OR A ROPEO R S O M E O T H E R I N S U L A T I N G M A T E R I A L

SEND FOR HELP AS SOON AS POSSIBLE

AFTER THE INJURED PERSON IS FREE OF CON-T A C T W I T H T H E S O U R C E O F E L E C T R I C A LS H O C K , M O V E T H E P E R S O N A S H O R TD I S T A N C E A W A Y A N D I M M E D I A T E L Y S T A R TA R T I F I C I A L R E S U S C I T A T I O N

TM 11-6130-416-14/EE010-BJ-JMA-010/E154 DCDUAL/T.O. 35C1-2-847-1

3-1 - 3-8

I N S E R T L A T E S T C H A N G E D P A G E S . D E S T R O Y S U P E R S E D E D P A G E S .

LIST OF EFFECTIVE PAGES

Dates of issue for original and changed pages are:

Original . . 0 . .

TOTAL NUMBER OF PAGES IN THIS PUBLICATION IS

Page # Change PageNo.

Title. . . . . . . . . .A. . . . . . . . . . . .i - vii. . . . . . . . .viii Blank. . . . . . . .1-1 - 1-4. . . . . . . .2-1 - 2-2. . . . . . . .

4-1 - 4-6..............5-1 - 5-23 . . . . . . . .5-24 - Blank . . . . . . . .A-1 . . . . . . . . . . .A-2 Blank. . . . . . . .B-1 - B-4 . . . . . . . .C-1 - C-2. . . . . . . .D-1 . . . . . . . . . . .D-2 Blank. . . . . . . .E-1 . . . . . . . . . . .E-2 Blank.... . . . .Index-1

- Index-10. . . .Report of Errors. . . . .FO-l - FO-2 . . . . . . .

No. No.

000000000000000000000

# Zero in this column indicates an original page.

83 CONSISTING OF THE FOLLOWING:

# Change Page # ChangeNo. No. No.

A

TM 11-6130-416-14/EE010-BJ-MMA-010/E154 DCDUAL/T.O.35Cl-2-847-1

WARNINGDANGEROUS VOLTAGE

Is Used in the Operation of this Equipment

DEATH ON CONTACT

may result if personnel fail to observe safety precautions

Never work on electronic equipment unless there is another personnearby who is familiar with the operation and hazards of the equipmentand who is competent in administering first aid. When the technicianis aided by operators, he must warn them about dangerous areas.

Whenever possible, the power supply to the equipment must be shut offbefore beginning work on the equipment. Take particular care toground every capacitor likely to hold a dangerous potential. Whenworking inside the equipment, after the power has been turned off,always ground every part before touching it.

Be careful not to contact high-voltage connections when installing oroperating this equipment.

Whenever the nature of the operation permits, keep one hand away fromthe equipment to reduce the hazard of current flowing through vitalorgans of the body.

Do not be misled by the term low voltage. Potentials as low as 50volts may cause death under adverse conditions.

B

TM 11-6130-416-14/EE010-BJ-MMA-010/E154 DCDUAL/T.0.35Cl-2-847-1

Do not touch heat sinks or power transistors mounted on

heat sinks as they may be very hot after the instrument

has been on and operating.

CAUTION

Do not directly short out any of the large capacitors as

it places too much stress on them. Discharge capacitors

through a load resistor.

C/(D blank)

This manual contains copyright material reproduced by permission of theHewlett-Packard Company.

TM 11-6130-416-14EE010-BJ-MMA-010/E154 DCDUAL

T.O.35C1-2-847-1

TECHNICAL MANUAL DEPARTMENTS OF THE ARMY,NO. 11-6130-416-14 THE NAVY,TECHNICAL MANUAL AND THE AIR FORCEEEO10-BJ-MMA-010/E154 DCDUALTECHNICAL ORDERNO. 35CI-2-847-I Washington, DC, 31 January 1983

OPERATORS, ORGANIZATIONAL, DIRECT SUPPORT, AND GENERAL SUPPORT

MAINTENANCE MANUAL

FOR

POWER SUPPLY, DUAL DC

(H-P Model 6255A)

(NSN 6130-00-065-6811)

REPORTING ERRORS AND RECOMMENDING IMPROVEMENTS

You can help improve this manual. If you find any mistakes orif you know of a way to improve the procedures, please let usknow. Mail your letter, DA Form 2028 (Recommended Changes toPublications and Blank Forms), or DA Form 2028-2 located in backof this manual direct to: Commander, US ArmyCommunications-Electronics Command and Fort Monmouth, ATTN:DRSEL-ME-MP, Fort Monmouth, NJ 07703.For Air Force, submit AFTO Form 22 (Technical Order System

Publication Improvement Report and Reply) in accordance withparagraph 6-5, Section VI, T.O. 00-5-1. Forward direct to primeALC/MST.For Navy, mail comments to the Commander, Naval Electronics

Systems Command, ATTN: ELEX 8122, Washington, DC 20360.In either case, a reply will be furnished direct to you.

This manual is an authentication of the manufacturers commercial literature which,through usage, has been found to cover the data required to operate and maintainthis equipment. Since the manual was not prepared in accordance with militaryspecifications and AR 310-3, the format has not been structured to consider levelsof maintenance.

i

TM 11-6130-416-14/EE010-BJ-MMA-010/E154 DCDUAL/T.O35C1-2-847-1

Section

TABLE OF CONTENTS

Page No.

I GENERAL INFORMATION . . . . . . . . . . . .1-11-A.1 Scope 1-11-A.31-A.41-A.61-A.8

1-A.9

1-A.11

1-A.13

1-A.15

1-A.18l-A.201-A.22

1-A.24

1-11-61-81-10

1-13

Index of Publications 1-1Army 1-1Air Force 1-1Maintenance Forms, 1-1Records and Reports

Reports of Maintenanceand UnsatisfactoryEquipment 1-1

Report of Packagingand Handling

Deficiencies 1-1Discrepancy in ShipmentReport (DISREP)(SF 361)

Reporting EquipmentImprovement

Recommendations (EIR)Air ForceNavyAdministrativeStorage

Destruction Of ArmyElectronics Materiel

DescriptionSpecificationsOptionsInstrument Identifica-tion

Ordering AdditionalManuals

1-1

1-11-1

1-1

1-21-21-21-3

1-3

1-3

II INSTALLATION . . . . . . . . . . . . . . . . . . .2-12-1 Initial Inspection 2-12-3 Mechanical Check 2-12-5 Electrical Check 2-12-7 Installation Data 2-12-9 Location 2-12-11 Rack Mounting 2-12-13 Input Power Requirements 2-12-15 Connections for 230 Volt

Operation 2-12-17 Power Cable 2-22-20 Repackaging for Shipment 2-2

III OPERATING INSTRUCTIONS . . . . . . . . . . .3-13-1 Operating Controls and

Indicators 3-1

Section

3 - 33 - 53-73 - 93-113-14

3-16

3-17

3-24

3-303-353-393-42

3-45

3-463-483-513-533-55

Page No.

Operating ModesNormal Operating ModeConstant VoltageConstant CurrentConnecting LoadOperation of SupplyBeyond Rated Output

Optional OperationalModesRemote Programming,Constant Voltage

Remote ProgrammingConstant CurrentRemote SensingSeries OperationParallel OperationAuto-TrackingOperationSpecial Operating Consid-erationsPulse LoadingOutput CapacitanceReverse Voltage LoadingReverse Current LoadingOvervoltage Protection

3-13-13-13-23-2

3-2

3-2

3-2

3-33-43-43-5

3-6

3-63-63-63-73-7

Crowbar 3-7IV PRINCIPLES OF OPERATION . . . . . . . ...4-1

4-1

4-54-84-94-144-16

4-20

4-254-28

4-314-34

Overall Block DiagramDiscussion 4-1

Simplified Schematic 4-2Detailed Circuit Analysis 4-3Feedback Loop 4-3Series Regulator 4-3Constant Voltage InputCircuit 4-3

Constant Current InputCircuit 4-4

Voltage Clamp Circuit 4-4Mixer and ErrorAmplifiers 4-4Reference Circuit 4-5Meter Circuit 4-5

V MAINTENANCE . . . . . . . . . . . . . . . . . . . . .5-15-1 Introduction 5-15-3 General Measurement

Techniques 5-15-8 Test Equipment

Required 5-2

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TM 11-6130-416-14/EE010-BJ-NMA-010/E154 DCDUAL/T.O.35Cl-2-847-1

Section

5-105-12

5-34

5-395-415-46

5-47A.15-47A.35-47A.5

5-47A.7

5-47A.9

5-47A.11

5-47A.13

5-47A.15

5-47A.17

5-47A.19

5-47A.21

5-47A.23

5-47A.25

5-47A.27

TABLE OF CONTENTS (CONTINUED)

Page No.

Performance TestConstant VoltageTests

Constant Current(CC) Tests

TroubleshootingTrouble AnalysisRepair and Replace-ment

Fuse ReplacementCover RemovalPower CableReplacement

Switch S1Replacement

Transformer T1ReplacementOvervoltageProtection CrowbarP.C. Board Replace-ment

Main Left P.C.Board Replacement(Viewed from Frontof Power Supply)

Main Right P.C.Board Replacement(Viewed from Frontof Power Supply)

Capacitator C14Replacement

Capacitors C5, C6Replacement

Power Transistor Q4,Q6, Replacement

Power Transistor Q7,Replacement

Transistor Q3Replacement

Voltage/CurrentProgramming ControlReplacement

5-2

5-2

5-85-95-9

5-145-155-15

5-17

5-17

5-17

5-18

5-18

5-18

5-19

5-19

5-19

5-20

5-20

5-20

Section Page No.

5-47A.29 Silicon RectifierCR19 Replacement

5-47A.31 Meter Switch S2Replacement

5-47A.33 Meter Replacement5-47A.35 Shunt Resistor

(R81, R82, or R83)Replacement

5-47A.37 Fuse Holder AssemblyReplacement

5-47A.39 Neon Lamp DS1Replacement

5-47A.41 Crowbar AdjustPotentiometer R5Replacement

5-48 Adjustment andCalibration

5-50 Meter Zero.5-52 Voltmeter Tracking5-54 Ammeter Tracking5-56 Constant Voltage

Programming Current5-59 Constant Current

Programming Current5-62 Reference Circuit

Adjustments5-64 Constant Voltage

Transient Response

5-20

5-215-21

5-21

5-21

5-21

5-22

5-225-225-225-22

5-22

5-23

5-23

5-23

VI REPLACEABLE PARTS . . . . . . . . . . . . . . .6-16-1 Introduction 6-16-4 Ordering Information 6-1

APPENDIX A . . . . . . . . . . . . . . . . . . . . . . . . . . A-1 APPENDIX B . . . . . . . . . . . . . . . . . . . . . . . . B-1APPENDIX C . . . . . . . . . . . . . . . . . . . . . . . . C-1APPENDIX D . . . . . . . . . . . . . . . . . . . . . . . D-1APPENDIX E . . . . . . . . . . . . . . . . . . . . . . . E-1INDEX Index 1

i i i


Page No.LIST OF ILLUSTRATIONSPage No. FigureFigure

1-12-13-1

3-23-3

3-4

3-5

3-6

3-73-8

3-9

3-10

3-11

3-12

3-13

4-1

4-2

Table1-15-15-25-3

5-4

5-5

DC Power SupplyPrimary ConnectionsFront Panel Control andIndicators

Normal Strapping PatternRemote ResistanceProgramming(ConstantVoltage)

v

2-1

3-13-1

3-2

3-3

3-3

3-33-4

3-4

3-5

3-5

3-5

3-6

3-8

4-14-2

4-3 Voltmeter Connections,Simplified Schematic

Ammeter Connections,Simplified Schematic

Front Panel TerminalConnections

Output CurrentMeasurement Technique

Differential VoltmeterSubstitute Test SetupOutput Current, TestSetup

4-5

4-54-4

5-1

5-25-1

5-1

5-2

5-2

5-3

5-4

5-5

5-6

5-75-8

5-9

5-10

5-11

5-12

5-13

Remote VoltageProgramming (ConstantVoltage)

Remote ResistanceProgramming (ConstantCurrent)

Remote VoltageProgramming (ConstantCurrent)

Remote SensingNormal Series Connec-tionsAuto-Series, Two andThree Units

Normal Parallel ,Connections

Auto-Parallel, Two andT h r e e U n i t s

Auto-Tracking, Two andThree Units

Model 6255A and 6289AOvervoltage ProtectionCrowbar

Overall BlockDiagramSimplified Schematic

Load Regulation, ConstantVoltage Test Setup 5-4

CV Ripple and Noise TestSetup 5-4

CV Noise Spike Test Setup 5-6Transient ResponseTest Setup 5-6Transient Response,Waveforms 5-6CV Programming, Speed,Test Setup 5-7

Output Impedance,Test Setup 5-7

CC Ripple and Noise TestSetup 5-8

Servicing Printed WiringBoards 5-13

Model 6255A ModularCabinet 5-166255A SchematicParts Location/Intercon-

5-14

FO-1FO-2

nection Diagram

LIST OF TABLES

Page No. TableSpecifications 1-4 5-6Test Equipment Required 5-3Common Troubles 5-9 5-7Reference, Bias, andFiltered DCTroubleshooting 5-11 5-8

Low Output VoltageTroubleshooting 5-11

High Output VoltageTroubleshooting 5-12

Page No.Selected SemiconductorCharacteristics 5-14

Checks and AdjustmentsAfter Replacement ofSemiconductor Devices 5-14

Calibration andAdjustment Summary 5-15

iv

TM 11-6130-416-14/EE010-BJ-MMA-010/E154 DCDUAL/T.0.35C1-2-847-1

Figure 1-1. Typical DPR Series DC Power Supply

v/(vi blank)

TM 11-6130-416-14/EE010-BJ-MMA-010/E154 DCDUAL/T.0.35C1-2-847-1

SECTION IGENERAL INFORMATION

1-A.1 SCOPE

1-A.2 This manual describes the Model6255A Dual DC Power Supply with Option11 Overvoltage Protection Crowbar Cir-cuit (power supply serial numbers2012A-4996 and up). Responsibilitiesfor all levels of maintenance are spec-ified by the Maintenance AllocationChart (MAC) contained in Appendix B.

1-A.3 INDEX OF PUBLICATIONS

1-A.4 ARMY

1-A.5 Refer to the latest issue of DAPAM 310-1 to determine whether thereare new editions, changes or additionalpublications pertaining to the equip-ment.

1-A.6 AIR FORCE

1-A.7 Use T.O. 0.1-31 Series Numeri-cal Index and Requirements Table(NIRT).

1-A.8 MAINTENANCE FORMS, RECORDS ANDREPORTS

1-A.9 REPORTS OF MAINTENANCE ANDUNSATISFACTORY EQUIPMENT

1-A.10 Department of the Army formsand procedures used for equipment main-tenance will be those prescribed by TM38-750, The Army Maintenance ManagementSystem (Army). Air Force personnelwill use AFM 66-1 for maintenance re-porting and T.O. 00-35D54 for unsatis-factory equipment reporting. Navy per-sonnel will report maintenance per-formed utilizing the Maintenance DataCollection Subsystem (MDCS) IAWOPNAVINST 4790.2, Vol 3, and unsatis-factory material/conditions (URsubmissions) IAW OPNAVINST 4790.2, Vol2, chapter 17.

1-A.11HANDLING

REPORT OF PACKAGING ANDDEFICIENCIES

1-A.12 Fill out and forward SD 364(Report of Discrepancy (ROD) as pre-scribed in AR 735-11-2/DLAR 4140.55/NAVMATINST 4355.73/AFR 400-54/MCO4430.3E.

1-A.13 DISCREPANCY IN SHIPMENT REPORT(DISREP) (SF 361)

1-A.14 Fill out and forward Discrep-ancy in Shipment Report (DISREP) (SF361) as prescribed in AR 55-38/NAVSUPINST 4610.33B/AFR 75-18/MCOP4610.19C/DLAR 4500.15.1-4.

1-A.15 REPORTING EQUIPMENTIMPROVEMENT RECOMMENDATIONS) (EIR)

1-A.16 ARMY

1-A.17 If the Power Supply, Dual DCneeds improvement, let us know. Sendus an EIR. You, the user, are theonly one who can tell us what is notliked about your equipment. Let usknow why you do not like the design.Tell us why a procedure is hard to per-form. Put it on an SF 368 (QualityDeficiency Report). Mail it to Comman-der, US Army Communications-ElectronicsCommand and Fort Monmouth, ATTN:DRSEL-ME-MP, Fort Monmouth, NJ 07003.We will send you a reply

1-A.18 AIR FORCE

1-A.19 Air Force personnel areencouraged to submit EIRs in accordancewith AFM 900-4.

1-A.20 NAVY

1-A.21 Navy personnel are encouragedto submit EIRs through their localBeneficial Suggestion Program.

1-A.22 ADMINISTRATIVE STORAGE

1-A.23 Refer to TM 11-5805-683-12 or

1-1


TM 11-5805-681-12, Administrative Stor-age. Administrative storage of equip-ment issued to and used by Army activi-ties will have preventive maintenanceperformed in accordance with the Pre-ventive Maintenance Checks and Services(PMCS) procedure listed before storing.When removing the equipment from admin-istrative storage,the PMCS should beperformed to assure operational readi-ness. Disassembly and repacking ofequipment for shipment or limited stor-age are also covered. Refer to TM 749-90-1 if there are no published PMcharts.

1-A.24 DESTRUCTION OF ARMYELETRONICS MATERIEL

1-A.25 Destruction of Army electron-ics materiel to prevent enemy use shallbe in accordance with TM 750-244-2.

1-1 DESCRIPTION

1-2 This power supply, Figure 1-1, iscompletely transistorized and suitablefor either rack or bench operation. Itis a dual supply consisting of two inde-pendently controlled sections; bothidentical to each other. These sectionswill be referred to as the left andright side power supplies as viewed fromfront of unit. Each section is a well-regulated,Constant Voltage/ConstantCurrent source that will furnish fullrated output voltage at the maximumrated output current or can be continu-ously adjusted throughout either outputrange. The front panel CURRENT controlscan be used to establish the output cur-rent limit (overload or short circuit)when the supply is used as a constantvoltage source and the VOLTAGE con-trol(s) can be used to establish thevoltage limit (ceiling) when the supplyis used as a constant current source.Each section will automatically cross-over from constant voltage to constantcurrent operation and vice versa if theoutput current or voltage exceeds thesepreset limits.

1-3 Each supply has both front and rear terminals.Either the positive or negative output terminal maybe grounded or the power supply can be operatedfloating at up to a maximum of 300 volts off ground.

1-4 Each section has its own front panel meterand operating controls. The meters are of the mul-tiple range type and can measure output voltage orcurrent. The voltage or current ranges are selectedby the applicable METER switch on the front panel.

1-5 TWO sets of programming terminals located atthe rear of the unit allow ease in adapting to themany operational capabilities of the power supply.A brief description of these capabilities is givenbelow:

a. Remote Programming

The power supply maybe programmedfrom a remote location by means of an externalvoltage source or resistance.

b. Remote Sensing

The degradation in regulation whichwould occur at the load because of the voltage dropin the load leads can be reduced by using the powersupply in the remote sensing mode of operation.

c. Series and Auto-Series Operation

Power supplies maybe used in serieswhen a higher output voltage is required in thevoltage mode of operation or when greater voltagecompliance is required in the constant current modeof operation. Auto-Series operation permits oneknob control of the total output voltage from amaster" supply.

d. Parallel and Auto-Parallel Operation

The power supply may be operated inparallel with a similar unit when greater output cur-rent capability is required. Auto-Parallel operationpermits one knob control of the total output currentfrom a master supply.

e. Auto-Tracking

The power supply maybe used as amaster supply, having control over one (or more)slave supplies that furnish various voltages fora system.

1-6 SPECIFICATIONS

1-7 Detailed specifications for the power supply

1-2

TM 11-6130-416-14/EE010-BJ-MM-010/E154 DCDUAL/T.O.35C1-2-847-1

are given in Table 1-1.

NOTESince both sections of this supplyare identical, only one section willbe discussed throughout the remain-ing portions of this manual. Alldescriptions, illustrations, tests,and adjustments apply equally toboth sections of the supply.

1-8 OPTIONS

1-9 Options are factory modifications of a stand-ard instrument that are requested by the customer.The following options are available for the instru-ment covered by this manual. Where necessary,detailed coverage of the options is included through-out the manual.

Option No.

07

08

09

10

11

Description

Voltage 10-Turn Pot: A single con-trol that replaces both coarse and finevoltage controls and improves outputsettability. Standard item on Model6258A power supplies.

Current 10-Turn Pot: A single con-trol that replaces both coarse and finecurrent controls and improves out putsettability.

Voltage and Current 10-Turn Pot:Consists of Options 07 and 08 on thesame instrument.

Chassis Slides: Enables convenientaccess to power supply interior formaintenance purposes.

Internal Overvoltage ProtectionCrowbars: This option includestwo crowbar circuits, one for eachpower supply within the 6253A oror 6255A. Each crowbar protectsdelicate loads by monitoring the out-put voltage and firing an SCR thatshorts the output when the presettrip voltage is exceeded. The circuitboards are factory installed withinthe supply. The Crowbar Adjustcontrols are mounted on the frontpanel to permit convenient adjust-ment.Trip Voltage Range:

6253A 6255A2.5 to 23V 2.5 to 44V

Trip Voltage Margin: The minimumcrowbar trip setting above the desiredoperating output voltage to preventfalse crowbar tripping is 4% of theoutput voltage setting +2V.

Refer to Paragraph 3-55 for detailsof operation and Figure 3-13 for theschematic diagram.

13 Three Digit Graduated Decadial Volt-age Control: Control that replacescoarse and fine voltage controls per-mitting accurate resettability.

14 Three Digit Graduated Decadial Cur-rent Control: Control that replacescoarse and fine current controls per-mitting accurate resettability.

28 Rewire for 230V AC Input: Supply asnormally shipped is wired for 115VACinput. Option 28 consists of recon-necting the input transformer for 230VAC operation.

1-10 INSTRUMENT IDENTIFICATION

1-11 Hewlett-Packard power supplies are identifiedby a three-part serial number tag. The first part isthe power supply model number. The second part isthe serial number prefix, which consists of a num-ber-letter combination that denotes the date of asignificant design change. The number designatesthe year, and the letter A through L designates themonth, January through December, respective y. Thethird part is the power supply serial number.

1-12 If the serial number prefix on your power sup-ply does not agree with the prefix on the title pageof this manual, change sheets are included to up-date the manual. Where applicable, backdatinginformation is given in an appendix at the rear ofthe manual.

1-13 ORDERING ADDITIONAL MANUALS

1-14 One manual is shipped with eachpower supply. Additional manuals maybe obtained from regular publicationdistribution channels.

1-3

TM 11-6130-416-14/EE010-BJ-MMA-010/E154 DCDUAL/T.0035C1-2-847-1

Table 1-1. Specifications

INPUT: OVERLOAD PROTECTION:105-125/210-250 VAC, single phase, A continuously acting constant current circuit

50-400 cps. protects the power supply for all overloads in-cluding a direct short placed across the termi-

OUTPUT: nals in constant voltage operation. The constantTwo independent outputs each of which can voltage circuit limits the output voltage in the

be set at 0-40 volts @ 0-1.5 amps. constant current mode of operation.

LOAD REGULATION: METERS:Constant Voltage -- Less than 0.01% plus Each front panel meter can be used as either a

2mv for a full load to no load change in output 0-50V or 0-5 volt voltmeter or as a 0-1.8A orcurrent. 0-0.18 amp ammeter.

Constant Current -- Less than 0.01% plus250a for a zero to maximum change in output OUTPUT CONTROLS:voltage. Coarse and fine voltage controls and coarse

and fine current controls set desired output volt-LINE REGULATION: age or current.

Constant Voltage -- Less than 0.01% plus2mv for any line voltage change within the input OUTPUT TERMINALS:rating. Six output posts (three per section)

Constant Current -- Less than 0.01% plus are provided on the front panel and output terminal250a for any line voltage change within the in- strips are located on the rear of the chassis. Allput rating. power supply output terminals are isolated from

the chassis and either the positive or negativeRIPPLE AND NOISE: terminals may be connected to the chassis

Constant Voltage -- Less than 200v rms. through a separate ground terminal located on theConstant Current -- Less than 500a rms. output terminal strip.

TEMPERATURE RANGES: ERROR SENSING:Operating: 0 to 50C. Storage: -20 to +85C. Error sensing is normally accomplished at the

front terminals if the load is attached to the frontTEMPERATURE COEFFICIENT: or at the rear terminals if the load is attached to

Constant Voltage -- Less than 0.02% plus the rear terminals. Also, provision is included500v per degree Centigrade. on the rear terminal strip for remote sensing.

Constant Current -- Less than 0.02% plus0.8ma per degree Centigrade. REMOTE PROGRAMMING:

Remote programming of the supply output at ap-STABILITY: proximately 200 ohms per volt in constant voltage

Constant Voltage -- Less than 0.10% plus is made available at the rear terminals. In con-2.5mv total drift for 8 hours after an initial warm- stant current mode of operation, the current canup time of 30 minutes at constant ambient, con- be remotely programmed at approximately 500 ohmsstant line voltage, and constant load. per ampere.

Constant Current -- Less than 0.10% plus4ma total drift for 8 hours after an initial warm-up COOLING:time of 30 minutes at constant ambient, constant Convection cooling is employed. The supplyline voltage, and constant load. has no moving parts.

OUTPUT IMPEDANCE (TYPICAL): SIZE:3- 1/2" H x 14- 1/2" D x 19 W. Easily rackApproximated by a 1 0 milliohm

mounted in a standard 19 relay rack.

resistance in series with a 1 WEIGHT:microhenry inductance. 28 lbs. net, 35 lbs. shipping.

TRANSIENT RECOVERY TIME: FINISH:Less than 50sec for output recovery to within Light gray front panel with dark gray case.

15 mv following a full load current change in theoutput. POWER CORD:

A three-wire, five-foot power cord is providedwith each unit.

1-4


SECTION IIINSTALLATION

2-1 INITIAL INSPECTION

2-2 Before shipment, this instrument was inspec-ted and found to be free of mechanical and electri-cal defects. As soon as the instrument is un-packed, inspect for any damage that may have oc-curred in transit. Save all packing materials untilthe inspection is completed.

2-3 MECHANICAL CHECK

2-4 This check should confirm that there are nobroken knobs or connectors, that the cabinet andpanel surfaces are free of dents and scratches,and that the meter is not scratched or cracked.

2-5 ELECTRICAL CHECK

2-6 The instrument should be checked against itselectrical specifications. Section V includes anin-cabinet performance check to verify properinstrument operation.

2-7 INSTALLATION DATA

2-8 The instrument is shipped ready for benchoperation. It is necessary only to connect theinstrument to a source of power and it is ready foroperation.

2-9 LOCATION

2-10 This instrument is air cooled. Sufficientspace should be allotted so that a free flow ofcooling air can reach the sides and rear of theinstrument when it is in operation. It should beused in an area where the ambient temperature doesnot exceed 50C.

2-11 RACK MOUNTING

2-12 This instrument is full rack size and can beeasily rack mounted in a conventional 19 inch rackpanel using standard mounting screws.

2-13 INPUT POWER REQUIREMENTS

2-14 This power supply may be operated from

eitherpower

a nominal 115 volt or 230 volt 50-400 cyclesource. The unit, as shipped from the fac-

tory, is wired for 115 volt operation. The inputpower required when operated from a 115 volt 60cycle power source at full load is 235 watts and2.6 amperes.

2-15 CONNECTIONS FOR 230 VOLT OPERATION(Figure 2-1)

Figure 2-1. Primary Connections

2-16 Normally, the two primary windings of the in-put transformer are connected in parallel for opera-tion from 115 volt source. To convert the powersupply to operation from a 230 volt source, thepower transformer windings are connected in seriesas follows:

2-1


a. Unplug the line cord and remove theunit covers.

b. Break the copper between 54 and 55 andalso between 50 and 51 on the printed circuitboard. These are shown in Figure 2-1, and arelabeled on copper side of printed circuit board.

c. Add strap between 50 and 55.d. Replace existing fuse with 2 ampere,

230 volt fuse. Return unit to case and operatenormally.

2-17 POWER CABLE

2-18 To protect operating personnel,the NationalElectrical Manufacturers Association(NEMA)rec-ommends that the instrument panel and cabinet begrounded. This instrument is equipped with athree conductor power cable. The third conductoris the ground conductor and when the cable isplugged into an appropriate receptacle, the in-strument is grounded. The offset pin on the power

cable three-prong connector is the ground connec-tion.

2-19 To preserve the protection feature whenoperating the instrument from a two-contact outlet,use a three-prong to two-prong adapter and con-nect the green lead on the adapter to ground.

2-20 REPACKAGING FOR SHIPMENT

2-21 To insure safe shipment of the instrument,it is recommended that the package designed forthe instrument be used. The original packagingmaterial is reusable.

2-2

TM ll-6130-416-14/EE010-BJ-MMA-010/E154 DCDUAL/T.O.35C1-2-847-1

SECTION IIIOPERATING INSTRUCTIONS

3-1 OPERATING CONTROLS AND INDICATORS

3-2 The front panel controls and indicators, to-gether with the normal turn-on sequence, areshown in Figure 3-1.

Figure 3-1. Front Panel Controls and Indicators

3-3 OPERATING MODES

3-4 The power supply is designed sothat its mode of operation can be se-lected by making strapping connectionsbetween particular terminals on theterminal strip at the rear of the powersupply. The terminal designations arestenciled in white on the power supplyabove their respective terminals.

Dangerous voltages exist inthis equipment. Be carefulwhen working with the powersupplies and their circuits.

Although the strapping patterns illus-trated in this section show the posi-tive terminal grounded, the operatorcan ground either terminal or operatethe power supply up to 300vdc offground(floating). The following para-

graphs describe the procedures for uti-lizing the various operational capabil-ities of the power supply. A more the-oretical description concerning the op-erational features of this supply iscontained in Application Note 90, DCPower Supply Handbook.

3-5 NORMAL OPERATING MODE

3-6 The power supply is normally shipped with itsrear terminal strapping connections arranged forConstant Voltage/Constant Current, local sensing,local programming, single unit mode of operation.This strapping pattern is illustrated in Figure 3-2.The operator selects either a constant voltage or aconstant current output using the front panel con-trols (local programming, no strapping changes arenecessary).

3-7for

3-8

Figure 3-2. Normal Strapping Pattern

CONSTANT VOLTAGE (See Figure 3-1controls and indicators.)

To select a constant voltage output, proceedas follows:

a. Turn-on power supply and adjust VOLTAGEcontrols for desired output voltage (output terminalsopen).

b. Short output terminals and adjust CUR-RENT controls for maximum output current allowable(current limit), as determined by load conditions.If a load change causes the current limit to be ex-ceeded, the power supply will automatically cross-over to constant current output at the preset currentlimit and the output voltage will drop proportionate-ly. In setting the current limit, allowance must bemade for high peak current which can cause un-wanted cross-over. (Refer to Paragraph 3-46.)

3-1

TM 11-6130-416-14/EE010-BJ-MMA-010/E154 DCDUAL/T.O.351-2-847-1

3-9 CONSTANT CURRENT (See Figure 3-1for controls and indicators.)3-10 To select a constant current output, proceedas follows:

a. Short output terminals and adjust CUR-RENT controls for desired output current.

b. Open output terminals and adjust VOLTAGEcontrols for maximum output voltage allowable (volt-age limit), as determined by load conditions. If aload change causes the voltage limit to be exceeded,the power supply will automatically y crossover toconstant voltage output at the preset voltage limitand the output current will drop proportionately. Insetting the voltage limit, allowance must be madefor high peak voltages which can cause unwantedcrossover. (Refer to Paragraph 3-46.)3-11 CONNECTING LOAD (See Figure 3-1for output terminals.)3-12 Each load should be connected to the powersupply output terminals using separate pairs of con-necting wires. This will minimize mutual couplingeffects between loads and will retain full advantageof the low output impedance of the power supply.Each pair of connecting wires should be as short aspossible and twisted or shielded to reduce noisepickup. (If shield is used, connect one end topower supply ground terminal and leave the otherend unconnected.)

3-13 If load considerations require that the outputpower distribution terminals be remotely locatedfrom the power supply, then the power supply out-put terminals should be connected to the remotedistribution terminals via a pair of twisted orshielded wires and each load separately connectedto the remote distribution terminals. For this case,remote sensing should be used (Paragraph 3-20).

3-14 OPERATION OF SUPPLY BEYOND RATED OUTPUT

3-15 The shaded area on the front panel meter faceindicates the amount of output voltage or currentthat is available in excess of the normal rated out-put. Although the supply can be operated in thisshaded region without being damaged, it cannot beguaranteed to meet all of its performance specif-ications. However, if the line voltage is main-tained above 115 Vac, the supply will probably op-erate

3-16

3-17

3-18

within its specifications.

OPTIONAL OPERATING MODES

REMOTE PROGRAMMING, CONSTANT VOLTAGE

The constant voltage output of the power sup-ply can be programmed (controlled) from a remotelocation if required. Either a resistance or voltage

source can be used for the programming device.The wires connecting the programming terminals ofthe supply to the remote programming device shouldbe twisted or shielded to reduce noise pick-up.The VOLTAGE controls on the front panel are dis-abled according to the following procedures.

3-19 Resistance Programming (Figure 3-3). In thismode, the output voltage will vary at a rate deter-mined by the programming coefficient (200 ohms perVolt for Models 6253A, 6255A, 6281A, 6284A, and6289A or 300 ohms per Volt for Models 6294A and6299A). The output voltage will increase 1 Volt foreach 200 ohms (or 300 ohms) added in series withthe programming terminals. The programming coeffi-cient is determined by the programming current. Thiscurrent is factory adjusted to within 2% of 5mA forModels 6253A, 6255A, 6281A, 6284A, and 6289A or2% of 3.3mA for Models 6294A and 6299A. If greater programming accuracy is required, it maybe achievedby changing resistor-R 13.

Figure 3-3. Remote Resistance Programming(Constant Voltage)

3-20 The output voltage of the power supply shouldbe zero Volts 2O millivolts when zero ohms is con-netted acress the programming terminals. If a zeroohm voltage closer than this is required, it may beachieved by changing resistor R6 or R8 as describedin Paragraph 5-59.

3-21 To maintain the stability and temperature co-efficient of the power supply, use programmingresistors that have stable, low noise, and lowtemperature (less than 30 ppm per degree Centi-grade)characteristics. A switch can be used inconjunction with various resistance values in orderto obtain discrete output voltages. The switchshould have make-before-break contacts to avoidmomentarily opening the programming terminalsduring the switching interval.

3-22 Voltage Programming (Figure 3-4). Employthe strapping pattern shown on Figure 3-4 for

3-2

m 11-6130-416-14/EEOI O-BJ-M.MA-0113/E154 DCDUAL/T.0.35Cl -2-847-l

Figure 3-4. Remote Voltage Programming(Constant Voltage)

voltage programming. In this mode, the output volt-age will vary in a 1 to 1 ratio with the programmingvoltage (reference voltage) and the load on the pro-gramming voltage source will not exceed 25mA.

3-23 The impedance matching resistor (Rx) for theprogramming voltage source should be approximately500 ohms to maintain the temperature and stabilityspecifications of the power SUPP1 y.

3-24 REMOlE PROGRAMMING, CONSTANTCURRENl! (Ses Figure 3-1 for controls andindicators. )3-25 Either a resistance or a voltage source can beused to control the constant current output of thesupply. The CURRENT controls on the front panelare disabled according to the following procedures.

3-26 Resistance Programming (Figure 3-5). In thismode, the outpdt current varies at a rate determinedby the programming coefficient 200 ohms per Ampfor Model 628 1A, 500 ohms per Ampere for Models6253A, 6255A, 6284A, and 6289A, and 1000 ohms perAmpere for Models 6294A and 6299A. The program-ming coefficient is determined by the Constant Cur-rent programming current (2mA for Models 6253A,6255A, 6284A, and 6289A, 5mA for Model 6281A lmAfor Model 6294A and 1.33mA for Model 6299A). Thiscurrent is adjusted to within 10% at the factory. Ifgreater programming accuracy is required, it maybea thieved by changing resistor R 19 as outlined inSection V.

AI A2A3A4A5A6A7A8A9 -S- GM++ SAIO

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- - - - -1 b- - - - -y

PROGRAMMINGRESISTOR

Figure 3-5. Remote Resistance Programming(Constant Current)

3-27 Use stable, low noise, low temperature coef-ficient (less than 3 Oppm/oC) programming resistorsto maintain the power supply temperature coefficientand stability specifications. A switch may be usedto set discrete values of output current. A make-before-break type of switch should be used sincethe output current will exceed the maximum ratingof the power supply if the switch contacts openduring the switching interval.

If the programming terminals (Al and AS)should open at any time during thismode, the output current will rise to avalue that may damage the power sup-ply and/or the load. To avoid thispossibility, connect a resistor acrossthe programming terminals having thevalue listed below. Like the program-ming resistor, this resistor should beof the low noise, low temperature coef-ficient type.

Model 6253 A,6284A 6255 A,6289A,6299AResistance 1. 5Kn 750n

Model 6281A, 6294AResistance lKA

3-28 Voltage Programming (Figure 3-6). In thismode, the output current will vary linearly withchanges in the programming voltage. The program-ming voltage should not exceed 1.2 Volts. Voltage inexcess of 1.2 Volts will result in excessive powerdissipation in the instrument and possible damage.

Al A2 A3 A4 AS A6 A? A8 A9 -S GNO + +S AIO

VOLTAGE

Figure 3-6. Remote Volta ge Programming(Constant Current)

3-29 The output current will be the programmingvoltage divided by 1 ohm. The current requiredfrom the voltage source will be less than 25 micro-a m p e r e . The impedance matching resistor (Rx)should be approximately 500 ohms if the temperaturecoefficient and stability specifications of the powersupply are to be maintained.

3 - 3


3-30 REMOTE SENSING (See Figure 3-7)

3-31 Remote sensing is used to maintain good regu-lation at the load and reduce the degradation of reg-ulation which would occur due to the voltage dropin the leads between the power supply and the load.Remote sensing is accomplished by utilizing thestrapping pattern shown in Figure 3-7. The pwersupply should be turned off before changing strap-ping patterns. The leads from the +S terminals tothe load will carry less than 10mA of current, andit is not required that these leads be as heavy asthe load leads. However, they must be twisted orshielded to minimize noise pick-up.

Observe polarity when connecting thesensing leads to the load.

Figure 3-7. Remote Sensing3-32 Note that it is desirable to minimize the dropin the load leads and it is recommended that thedrop not exceed 1 Volt per lead if the power supplyis to meet its dc specifications. If a larger dropmust be tolerated, please consult a Hewlett-Packardfield representative.

NOTE

Due to the voltage drop in the loadleads, it may be necessary to readjustthe current limit in the remote sensingmode.

3-33 The procedure just described will result in alow dc output impedance at the load. If a low acimpedance is required, it is recommended that thefollowing precautions be taken:

a. Disconnect output capacitor C20 by dis-connecting the strap between A9 and -S.

b. Connect a capacitor having similar char-acteristics (approximately same capacitance, samevoltage rating or greater, and having good high fre-quency characteristics) across the load using shortleads.

3-34 Although the strapping patterns shown in Fig-ures 3-3 through 3-6 employ local sensing, note

that i t is possible to operate a power supply s imul-taneously in the remote sensing and Constant Volt-age/Constant Current remote programming modes.

3-35 SERIES OPERATION3-36 Normal Series Connections (Figure 3-8). Two

or more power supplies can be operated in series toobtain a higher voltage than that available from asingle supply. When this connection is used, theoutput voltage is the sum of the voltages of the in-dividual supplies. Each of the individual suppliesmust be adjusted in order to obtain the total outputvoltage. The power supply contains a protectivediode connected internally across the output whichprotects the supply if one power supply is turned offwhile its series partner(s) is on.

Figure 3-8. Normal Series Connections

3-37 Auto-Series Connections (Figure 3-9). TheAuto-Series configuration is used when it is desir-able to have the output voltage of each of the seriesconnected supplies vary in accordance with thesetting of a control unit. The control unit is calledthe master; the controlled units are called slaves.At maximum output voltage, the voltage of theslaves is determined by the setting of the frontpanel VOLTAGE control on the master. The mastersupply must be the most positive supply of theseries. The output CURRENT controls of all seriesunits are operative and the current limit iS equal tothe lowest control setting. If any output CURRENTcontrols are set too low, automatic crossover toconstant current operation will occur and the out-put voltage will drop. Remote sensing and pro-gramming can be used; however, the strapping ar-rangements shown in the applicable figures showlocal sensing and programming.

3-38 In order to maintain the temperature coeffic-ient and stability specifications of the power supply, the external resistors (Rx) shown in Figure 3-9should be stable, low noise, low temperature co-efficient (less than 30 ppm per degree Centigrade)resistors. The value of each resistor is dependant

3 - 4

TM 11-6130-416-14/EE010-BJ-MMA-010/E154 DCDUAL/T.O.35Cl-2-847-1

on the maximum voltage rating of the master sup-ply. The value of Rx is this voltage divided by thevoltage programming current of the slave supply(1/Kp where KP is the voltage programming coef-ficient). The voltage contribution of the slave isdetermined by its voltage control setting.

Figure 3-9. Auto-Series, Two and Three Units

3-39 PARALLEL OPERATION (See Figure 3-1f o r c o n t r o l s a n d i n d i c a t o r s . )3-40 Normal Parallel Connections (Figure 3-10).Two or more power supplies can be connected inparallel to obtain a total output current greater thanthat available from one power supply. The totaloutput current is the sum of the output currents ofthe individual power supplies. The output CURRENT

controls of each power supply can be separatelyset. The output voltage controls of one power sup-ply should be set to the desired output voltage;the other power supply should be set for a slightlylarger output volts ge. The supply set to the loweroutput voltage will act as a constant voltagesource; the supply set to the higher output will actas a constant current source, dropping its output

Figure 3-10. Normal Parallel Connections

Figure 3-11. Auto-Parallel, Two and Three Units

3 - 5


voltage until it equals that of the other supply. Theconstant voltage source will deliver only that frac-tion of its total rated output current which is neces-sary to fulfill the total current demand,

3-41 Auto-Parallel. The strapping patterns forAuto-Parallel operation of two power supplies areshown in Figure 3-11. Auto-Parallel operationpermits equal current sharing under all load con-ditions, and allows complete control of output cur-rent from one master power supply. The output cur-rent of each slave will be approximately equal tothe masters regardless of the load conditions.Because the output current controls of each slaveare operative, the y should be set to maximum toavoid having the slave revert to constant currentoperation; this would occur if the master outputcurrent setting exceeded the slaves.

Figure 3-12. Auto-Tracking, Two and Three Units

3-42 AUTO-TRACKING OPERATION (See Figure 3-12)

3-43 The Auto-Tracking configuration is used whenit is necessary that several different voltages re-ferred to a common bus, vary in proportion to thesetting of a particular instrument (the control ormaster). A fraction of the masters output voltageis fed to the comparison amplifier of the slave sup-ply, thus controlling the slaves output. The mastermust have the largest output voltage of any powersupply in the group (must be the most positive sup-ply in the example shown on Figure 3-12).

3-44 The output voltage of the slave is a percent-age of the master's output voltage, and is deter-mined by the voltage divider consisting of Rx (or Rxand Ry) and the voltage control of the slave supply,Rp. where: ES=EMRp/Rx+Rp. Turn-on and turn-offof the power supplies is controlled by the master.Remote sensing and programming can be used; al-though the strapping patterns for these modes showonly local sensing and programming. In order tomaintain the temperature coefficient and stabilityspecifications of the power supply, the external re-sistors should be stable, low noise, low temperature(less than 30ppm per C) resistors.

3-45 SPECIAL OPERATING CONSIDERATIONS

3-46 PULSE LOADING

3-47 The power supply will automatically cross-over from constant voltage to constant current oper-ation, or the reverse, in response to an increase(over the preset limit) in the output current or volt-age, respective y. Although the preset limit may beset higher than the average output current or voltage,high peak currents or voltages (as occur in pulseloading) may exceed the preset limit and causecrossever to occur. If this crossover limiting is notdesired, set the preset limit for the peak require-ment and not the average.

3-48 OUTPUT CAPACITANCE

3-49 An internal capacitor, connected acress theoutput terminals of the power supply, helps to sup-ply high-current pulses of short duration duringconstant voltage operation. Any capacitance addedexternally will improve the pulse current capability,but will decrease the safety provided by the con-stant current circuit. A high-current pulse may dam-age load components before the average output cur-rent is large enough to cause the constant currentcircuit to operate.

3-50 The effects of the output capacitor duringconstant current operation are as follows:

a. The output impedance of the power supply

3-6


decreases with increasing frequency.b. The recovery time of the output voltage is

longer for load resistance changes.c. A large surge current causing a high pow-

er dissipation in the load occurs when the load re-sistance is reduced rapidly.

3-51 REVERSE VOLTAGE LOADING

3-52 A diode is connected across the output termi-nals. Under norms 1 operating conditions, the diodeis reverse biased (anode connected to negative ter-minal). If a reverse voltage is applied to the outputterminals (positive voltage applied to negative ter-minal), the diode will conduct, shunting currentacross the output terminals and limiting the voltageto the forward voltage drop of the diode. This diodeprotects the series transistors and the output elec-trolytic capacitor.

3-53 REVERSE CURRENT LOADING

3-54 Active loads connected to the power supplymay actually deliver a reverse current to the powersupply during a portion of its operating cycle. Anexternal source cannot be allowed to pump currentinto the supply without loss of regulation and pos-sible damage to the output capacitor. To avoidthese effects, it is necessary to preload the sup-ply with a dummy load resistor so that the powersupply delivers current through the entire operatingcycle of the load device.

3-55 OVERVOLTAGE PROTECTION CROWBAR(See Figure 3-1 for controls andindicators and Figure 3-13 for theschematic diagram.)

3-56 Use the following steps to adjustthe crowbar circuit.

a. Turn CROWBAR ADJUST fullyclockwise to set trip voltage tomaximum.

b. Set power supply VOLTAGEcontrol for desired crowbar tripvoltage. To prevent false crowbartripping, trip voltage should exceeddesired output voltage by the followingamount: 4% of the output voltage plus2V.

c. Slowly turn CROWBAR ADJUSTccw until crowbar trips, output goes toOV or a small positive voltage.

d. Crowbar will remain activatedand output shorted until supply isturned off. To reset crowbar, turnsupply off, then on.

e. If CROWBAR must be completelydisabled, remove lead attached toCROWBAR ADJUST potentiometer R5.

3-7


Figure 3-13. Model 6255A and 6289A Overvoltage Protection Crowbar

3-8

Figure 4-1.


SECTION IVPRINCIPLES OF OPERATION

4-1 OVERALL BLOCK DIAGRAM DISCUSSION

4-2 The power supply, as shown on the overallblock diagram on Figure 4-1, consists of a powertransformer, a rectifier and filter, a series regu-lator, the mixer and error amplifiers, an ORgate, a constant voltage input circuit, a constantcurrent input circuit, a reference regulator circuit,a bias supply, and a metering circuit.

4-3 The input line voltage passes through thepower transformer to the rectifier and filter.The rectifier-filter converts the AC input to rawDC which is fed to the positive terminal via theregulator and current sampling resister network.The regulator, part of the feedback loop, is madeto alter its conduction to maintain a constant out-put voltage or current. The voltage developed

across the current sampling resistor network is theinput to the constant current input circuit. Theconstant voltage input circuit obtains its input bysampling the output voltage of the supply.

4-4 Any changes in output voltage/current aredetected in the constant voltage/constant currentinput circuit, amplified by the mixer and error am-plifiers, and applied to the series regulator in thecorrect phase and amplitude to counteract thechange in output voltage/output current. The refer-ence circuit provides stable reference voltageswhich are used by the constant voltage/current in-put circuits for comparison purposes. The biassupply furnishes voltages which are used through-out the instrument for biasing purposes. The metercircuit provides an indication of output voltage orcurrent for both operating modes.

4-1

Figure 4-2.


4-5 SIMPLIFIED SCHEMATIC (See Figure3-1 for controls and indicators.)4-6 A simplified schematic of the power supplyis shown in Figure 4-2. It shows the operatingcontrols; the ON-off switch, the voltage and cur-rent programming controls R10 and R16. Figure4-2 also shows the internal sources of bias andreference voltages and their nominal magnitudeswith an input of 115 VAC.

4-7 Diode CR34, connected across the output

terminals of the power supply, is a protective de-vice which prevents internal damage that mightoccur if a reverse voltage were applied across theoutput terminals. Output capacitor, C20, is alsoconnected across the output terminals when thenormal strapping pattern shown on Figure 4-2 isemployed. Note that this capacitor can be removedif an increase in the programming speed is desired.Under these conditions, capacitor C19 serves toinsure loop stability.

4-2


4-8 DETAILED CIRCUIT ANALYSIS [Referto overall schematic diagram (FO-1) atrear of manual.]4-9 FEEDBACK LOOP (See Figure 3-1 forcontrols and indicators.)4-10 The feedback loop functions continuously tokeep the output voltage constant, during constantvoltage operation, and the output current constant,during constant current operation. For purposes ofthis discussion, assume that the unit is in con-stant voltage operation and that the programmingresistors R10 A and B have been adjusted so thatthe supply is yielding the desired output voltage.Further assume that the output voltage instanta-neously rises (goes positive) due to a variation inthe external load circuit.

4-11 Note that the change maybe in the form of aslow rise in the output voltage or a positive goingAC signal. An AC signal is coupled to summingpoint A6 through capacitor C1 and a DC voltage iscoupled to A6 through R10.

4-12 The rise in output voltage causes the voltageat A6 and thus the base of Q1A to decrease (gonegative). Q1A now decreases its conduction andits collector voltage rises. The positive going er-ror voltage is amplified and inverted by Q3 and fedto the bases of series transistors Q6 and Q7 viaemitter followers Q5 and Q4. The negative goinginput causes Q6 and Q7 to decrease their conduc-tion so that they drop more of the line voltage, andreduce the output voltage to its original level.

4-13 If the external load resistance is decreasedto a certain crossover point, the output current in-creases until transistor Q2A begins to conduct.During this time, the output voltage has also de-creased to a level so that the base of Q1A is at ahigh positive potential. With Q1A in full conduc-tion, its collector voltage decreases by the amountnecessary to back bias OR gate diode CR3 and thesupply is now in the constant current mode of op-eration. The crossover point at which constantcurrent operation commences is determined by thesetting of CURRENT control R16. The operation ofthe feedback loop during the constant current op-erating mode is similar to that occuring duringconstant voltage operation except that the input tothe differential amplifier comparison circuit is ob-tained from the current sampling resistor network.

4-14 SERIES REGULATOR

4-15 The series regulator consists of transistorstages Q6 and Q7 (see schematic at rear of manual).Transistor Q6 is the series element, or pass transis-tor, which controls the output. Transistor Q7, to-gether with shunt resistors R81, R82, and R83, areconnected in a manner which minimizes the power

dissipated in series transistor Q6. The bias voltagefor Q7 is developed across zener diode VR5, TheThe conduction of Q7 will decrease as the collector-to-emitter voltage of Q6 approaches the voltagedeveloped across the biasing diodes, At low out-put voltages Q7 is completely cutoff and all of theload current flows through the shunt resistors. Thevoltage that is dropped acress Q7 and the shuntresistors reduces the voltage dropped across Q6,thus diminishing its power dissipation. The reli-ability of the regulator is further increased bymounting the shunt resistors outside the rear ofthe cabinet so that the internal components areoperated under lower temperature conditions.Diode CR11, connected across Q6, protects it fromreverse voltages that could develop across it dur-ing parallel or auto-parallel operation if one sup-ply is turned on before the other. Diodes CR18and CR19 perform a similar function for Q7.

4-16 CONSTANT VOLTAGE INPUT CIRCUIT(See Figure 3-1 for controls and in-dicators.)4-17 The circuit consists of programming resistorR10A and B, and a differential amplifier stage (Q1and associated components). Transistor Q1 con-sists of two transistors housed in a single package.The transistors have matched characteristics min-imizing differential voltages due to mismatchedstages. Moreover, drift due to thermal differen-tials is minimized, since both transistors operateat essentially the same temperature.

4-18 The constant voltage input circuit continu-ously compares a fixed reference voltage with aportion of the output voltage and, if a differenceexists, produces an error voltage whose amplitudeand phase is proportional to the difference. Theerror output is fed back to the series regulator,through an OR gate and the mixer/error amplifiers.The error voltage changes the conduction of theseries regulator which, in turn, alters the outputvoltage so that the difference between the two in-put voltages applied to the differential amplifier isreduced to zero. The above action maintains theoutput voltage constant.

4-19 Stage Q1B of the differential amplifier isconnected to a common (+S) potential through im-pedance equalizing resistor R5. Resistors R6 andR8 are used to zero bias the input stage, offsettingminor base-to-emitter voltage differences in Q1.The base of Q1A is connected to a summing point atthe junction of the programming resistor and thecurrent pullout resistor, R12. Instantaneouschanges in output voltage result in an increase ordecrease in the summing point potential. Q1A isthen made to conduct more or less, in accordancewith the summing point voltage change. The re-

4-3


sultant output error voltage is fed back to theseries regulator via OR-gate diode CR3 and theremaining components of the feedback loop, Re-sistor R1, in series with the base of Q1A, limitsthe current through the programming resistor duringrapid voltage turn-down. Diodes CR1 and CR2form a limiting network which prevent excessivevoltage excursions from over driving stage Q1A.Capacitors C1 and C2, shunting the programmingresistors, increase the high frequency gain of theinput amplifier. Resistor R13, shunting pulloutresistor R12, serves as a trimming adjustment forthe programming current.

4-20 CONSTANT CURRENT INPUT CIRCUIT(See Figure 3-1 for controls and in-dicators.)

4-21 This circuit is similar in appearance and op-eration to the constant voltage input circuit. Itconsists basically of the current programming re-sistors R16A and B, and a differential amplifierstage (Q2 and associated components). Liketransistor Q1 in the voltage input circuit, Q2 con-sists of two transistors, having matched charac-teristics, that are housed in a single package.

4-22 The constant current input cir-cuit continuously compares a fixed ref-erence voltage with the voltage dropacross the current sampling resistorR54. If a difference exists, the dif-ferential amplifier produces an errorvoltage which is proportional to thisdifference. The remaining componentsin the feedback loop (amplifiers andseries regulator) function to maintainthe drop across the current samplingresistors, and consequently the outputcurrent, at a constant value.

4-23 Stage Q2B is connected to a common (+S) po-tential through impedance equalizing resistor R26.Resistors R25 and R28 are used to zero bias the in-put stage, offsetting minor base-to-emitter voltagedifferences in Q2. Instantaneous changes in out-put current on the positive line are felt at the cur-rent summing point and, hence, the base of Q2A.Stage Q2A varies its conduction in accordancewith the polarity of the change at the summingpoint. The change in Q2As conduction also variesthe conduction of Q2B due to the coupling effectsof the common emitter resister, R22. The errorvoltage is taken from the collector of Q2B and fedback to the series regulator through OR-gate diodeCR4 and the remaining components of the feedbackloop. The error voltage then varies the conductionof the regulator so that the output current is main-tained at the proper level.

4-24 Resistor R20, in conjunction with R21 and C3helps stabilize the feedback loop, Diode CR5 lim-its voltage excursions on the base of Q2A. Resis-ter R19, shunting the pullout resistor, serves as atrimming adjustment for the programming currentflowing through R16.

4-25 VOLTAGE CLAMP CIRCUIT

4-26 During constant current operation the con-stant voltage programming resisters are a shuntload acress the output terminals of the power sup-ply. If the output voltage changed, the currentthrough these resistors would tend to change re-sulting in an output current change. The clampcircuit is a return path for the voltage programmingcurrent, the current that normally flows through theprogramming resistors. The circuit maintains thecurrent into the constant voltage summing point(A6) constant, thus eliminating the error due toshunting effects of the constant voltage program-ming resistors.

4-27 The voltage divider, R51, R52, and VR3,back biases CR30 and Q1O during constant voltageoperation. When the power supply goes into con-stant current operation, CR30 becomes forwardbiased by the collector voltage of Q1A. This re-sults in conduction of Q1O and the clamping of thesumming point at a potential only slightly morenegative than the normal constant voltage potential.Clamping this voltage at approximately the samepotential that exists in constant voltage operation,results in a constant voltage across, and conse-quently a constant current through the pullout re-sistor (R12).

4-28 MIXER AND ERROR AMPLIFIERS

4-29 The mixer and error amplifiers amplify theerror signal from the constant voltage or constantcurrent input circuit to a level sufficient to drivethe series regulator transistors. The emitter biaspotential for mixer amplifier Q3 is established bythe emitter follower. Transistor Q3 receives theerror voltage input from either the constant voltageor constant current circuit via the OR-gate diode(CR3 or CR4) that is conducting at that time.Diode CR3 is forward biased, and CR4 reversedbiased, during constant voltage operation. Thereverse is true during constant current operation.

4-30 The RC network, composed of C5 and R30, isan equalizing network which provides for high fre-quency roll off in the loop gain response in order tostabilize the feedback loop. Emitter follower tran-sistors Q4 and Q5 are the error amplifiers servingas the driver and predriver elements, respectively,for the series regulator. Transistor Q4, together

4-4


with diode CR17, provides a low resistance dis-charge path for the output capacitance of the powersupply during rapid down programming.

4-31 REFERENCE CIRCUIT

4-32 The reference circuit is a feedback powersupply similar to the main supply. It providesstable reference voltages which are used through-out the unit. The reference voltages are all de-rived from smoothed DC obtained from the fullwave rectifier (CR22 and CR23) and filter capacitorC10. The +6.2 and -6.2 voltages, which are usedin the constant voltage and current input circuitsfor comparison purposes, are developed acrosstemperature compensated Zener diodes VR1 andVR2. Resister R43 limits the current through theZener diodes to establish an optimum bias level.

4-33 The regulating circuit consists of series reg-ulating transistor Q9 and error amplifier Q8. Out-put voltage changes are detected by Q8 whose baseis connected to the junction of a voltage divider(R41, R42) connected directly across the supply. Anyerror signals are amplified and inverted by Q8 andapplied to the base of series transistor Q9. Theseries element then alters its conduction in thedirection and by the amount necessary to maintainthe voltage across VR1 and VR2 constant. ResistorR46, the emitter resistor for Q8, is connected in amanner which minimizes changes in the referencevoltage caused by variations in the input line.Output capacitor C9 stabilizes the regulator loop.4-34 METER CIRCUIT (See Figure 3-1 forcontrols and indicators.)4-35 The meter circuit provides continuous indica-tions of output voltage or current on a single multi-ple range meter. The meter can be used either as avoltmeter or an ammeter depending upon the positionof the METER switch S2 on the front panel of thesupply. This switch also selects one of two meterranges on each scale. The meter circuit consistsbasically of a selection circuit (switch S2 and asso-ciated voltage dividers), stable differential amplifierstages (Q11, Q12, and Q14), and the meter move-ment.

4-36 The selection circuit determines which volt-age divider is connected to the differential ampli-fier Input. When the METER section of S2 is inone of the voltage positions, the voltage acrossdivider R59, R60, and R61 (connected across theoutput of the supply is the input to the differen-tial amplifier.

4-37 When S2 is in one of the current positionsthe voltage acress divider R56, R57, and R58 isthe input to the differential amplifier. Note that

this divider is connected across the sampling re-sistor network. The amplified output of the differ-ential amplifier is used to deflect the meter.

4-38 The differential amplifier is a stable devicehaving a fixed gain of ten, Stage Q11B of the am-plifier receives a negative voltage from the appli-cable voltage divider when S2 is in one of thevoltage positions while stage Q11A is connectedto the +S (common) terminal. With S2 in a currentposition, stage Q11A receives a positive voltagefrom the applicable voltage divider while stageQ11B is connected to the +S terminal. The differ-ential output of the amplifier is taken from thecollectors of Q12 and Q14. Transistor Q15 is aconstant current source which sets up the properbias current for the amplifier. Potentiometer R63permits zeroing of the meter.

4-39 The meter amplifier contains an inherentcurrent limiting feature which protects the metermovement against overloads. For example, ifMETER switch S2 is placed in the low currentrange when the power supply is actually deliver-ing a higher ampere output, the differential ampli-fiers are quickly driven into saturation limiting thecurrent through the meter to a safe value.

Figure 4-3. Voltmeter Connections,Simplified Schematic

Figure 4-4. Ammeter Connections,Simplified Schematic

4-5


4-40 Figures 4-3 and 4-4 show the meter connec-tions when the METER section of S2 is in thehigher voltage and current range positions, respec-tively. For the sake of simplicity, some of theactual circuit components are not shown on thesedrawings, With the METER switch in the highervoltage range, position 2, the voltage drop acressR59 is the input to the meter amplifier and themeter indicates the output voltage acress the +Sand -S terminals. For low output voltages, S2 canbe switched to the low voltage position (1) result-ing in the application of a larger percentage of the

output voltage (drop acress R59 and R60) to themeter amplifier.

4-41 As illustrated in Figure 4-4 with the METERswitch in the high current position (3) the voltagedrop across R58 is applied to the meter amplifierand the meter indicates the output current whichflows through the sampling resistor network. Forlow values of output current, the METER switchcan be set to position 4 and the voltage drop acrossR57 and R58 is applied to the meter amplifier.

4-6


SECTION VMAINTENANCE

5-1 INTRODUCTION

CAUTION

Do not directly short outany of the large capacitorsas it places too much stresson them. Discharge capaci-tors through a loadresistor.

shown in Figure 5-1. The performance characteris-tics should never be measured on the front terminalsif the load is connected across the rear terminals.Note that when measurements are made at the frontterminals, the monitoring leads are connected at A,not B, as shown in Figure 5-1. Failure to connectthe measuring device at A will result in a measure-ment that includes the resistance of the leads be-tween the output terminals and the point of connec-tion.

5-2 Upon receipt of the power supply, the per-formance check (Paragraph 5-10) should be made.This check is suitable for incoming inspection. Ifa fault is detected in the power supply while makingthe performance check or during normal operation,proceed to the troubleshooting procedures (Para-graph 5-41). After trouble shooting and repair (Para-graph 5-46), perform any necessary adjustmentsand calibrations (Paragraph 5-48). Before returningthe power supply to normal operation, repeat theperformance check to ensure that the fault has beenproperly corrected and that no other faults exist.Before doing any maintenance checks, turn on pow-er supply, allow a half-hour warm-up, and read thegeneral information regarding measurement tech-niques (Paragraph 5-3).

5-3 GENERAL MEASUREMENT TECHNIQUES

DO not touch heat sinks orpower transistors mountedon heat sinks as they arevery hot after instrumenthas been on and operating.

5-4 The measuring device must be connectedacross the sensing leads of the supply or as closeto the output terminals as possible when measuringthe output impedance, transient response, regula-tion, or ripple of the power supply in order toachieve valid measurements. A measurement madeacross the load includes the impedance of the leadsto the load and such lead lengths can easily havean impedance several orders of magnitude greaterthan the supply impedance, thus invalidating themeasurement.

5-5 The monitoring device should be connectedto the +S and -S terminals (see Figure 3-2) or as

Figure 5-1. Front Panel Terminal Connections

5-6 For output current measurements, the currentsampling resistor should be a four-terminal resis-tor. The four terminals are connected as shown inFigure 5-2. In addition, the resister should be ofthe low noise, low temperature coefficient (lessthan 30ppm/C) type and should be used at nomore than 5% of its rated power so that its temper-ature rise will be minimized.

Figure 5-2. Output Current Measurement Technique

5-7 When using an oscilloscope, ground one ter-minal of the power supply and then ground the caseof the oscilloscope to this same point. Make cer-tain that the case is not also grounded by someother means (Power line). Connect both oscillo-scope input leads to the power supply ground termi-nal and check that the oscilloscope is not exhibi-ting a ripple or transient due to ground loops, pick-up, or other means.

5-1


5-8 TEST EQUIPMENT REQUIRED

5-9 Table 5-1 lists the test equipment required toperform the various procedures described in thisSection.

C A U T I O N

Care must be exercised when using anelectronic null detector in which oneinput terminal is grounded to avoidground loops and circulating currents.

Figure 5-3. Differential Voltmeter Substitute,Test Setup

5-10 PERFORMANCE TEST

5-11 The following test can be used as an incom-ing inspection check and appropriate portions of thetest can be repeated either to check the operation ofthe instrument after repairs or for periodic mainte-nance tests. The tests are performed using a 115Vac60Hz, single phase input power source. If the cor-rect result is not obtained for a particular check,do not adjust any controls; proceed to trouble-shooting (Paragraph 5-41).

5-12 CONSTANT VOLTAGE (CV) TESTS (SeeFigure 3-1 for controls and indicators.)

5-13 Rated Output and Meter Accuracy.

5-14 Voltage. Proceed as follows:a. Connect load resistor across rear output

terminals of supply. Resistor value to be as fol-lows:Model 6253A 6255A 6281A 6284A 6289A 6294AResistance 6 26 26 60

b. Connect differential voltmeter across +Sand -S terminals of supply observing correct polar-ity.

c. Set METER switch to highest voltagerange and turn on supply.

d. Adjust VOLTAGE control(s) until frontpanel meter indicates exactly the maximum ratedoutput voltage.

e. Differential voltmeter should indicatemaximum rated output voltage within 2%.

5-15 Current. Proceed as follows:a. Connect test setup as shown in Figure

5-4 leaving switch S1 open.b. Turn CURRENT controls fully clockwise.c. Set METER switch to highest current

range and turn on supply.d. Adjust VOLTAGE control(s) until front

panel meter indicates exactly the maximum ratedoutput current.

e. Differential voltmeter should read 1.0 0.02 Vdc.

Figure 5-4. Output Current Test Setup

5-16. Load Regulation. To check constant voltageload regulation, proceed as follows:

a. Connect test setup as shown in Figure 5-5.b. Turn CURRENT controls fully clockwise.c. Set METER switch to highest current


panel meter indicates exactly the maximum ratedoutput voltage.

e. Read and record voltage indicated on dif-ferential voltmeter.

f. Disconnect load resistors.g. Reading on differential voltmeter should

not vary from reading recorded in step e by morethan the following:

1.5 6

5-2


Table 5-1. Test Equipment Required

TYPEREQUIRED USE RECOMMENDEDCHARACTERISTICS MODEL

Differential Sensitivity: 1mV full scale (min.). Measure DC voltages; 3420 (See Note)

Voltmeter Input impedance: 10 megohms (min.). calibration proceduresVariable Range: 90-130 volts. Equipped with Vary AC input ---Voltage voltmeter accurate within 1 volt.TransformerAC Voltmeter Accuracy: 2%. Sensitivity: 1mV full Measure AC voltages and 403B

scale deflection (min.). rippleOscilloscope Sensitivity: 10OV/cm. Differential Display transient response 140A plus 1400A

input. waveforms plug-in. 1402Aplug-in for spikemeasurements o n l y ,

Oscillator Range: 5 Hz to 600 kHz. Accuracy: Impedance checks 200 CD2%. Output: 1OV rms.

DC Voltmeter Accuracy: 1%. Input resistance: Measure DC voltages 412A20, 000 ohms/volt (min.).

Repetitive Rate: 60-400 Hz, 2sec rise and Measure transient See Figure 5-8,Load Switch fall time. response

Resistive Values: See Paragraph 5-14 and Power supply load resis- ---Loads Figure 5-4. 5%, 75 watts. tors

Current 6253A, 6284A: O.33 Measure current; cal- See Parts ListSampling 6255A, 6289A: O.66 ibrate meter; con- R54Resistor 6281A: 0.2

6294A:stant current (CC)

1 ripple and noiseResistor 1%, 2 watt non-inductive. Measure impedance ---

Resistor 100 ohms, 5%, 10 watt. Measure impedance ---

Resistor Value: See Paragraph 5-59. 0.1%, Calibrate programming ---1/2 watt. current

Resistor Value: See Paragraph 5-62. 0.1% Calibrate programming ---1/2 watt. current

Capacitor 500f, 50 wVdc. Measure impedance ---

Decade Range: 0-500K. Accuracy: 0.1% Measure programming ---Resistance plus 1 ohm. Make-before-break coefficientsBox contacts.

1

NOTE

A satisfactory substitute for a differential voltmeter is to arrange a reference voltagesource and null detector as shown in Figure 5-3. The reference voltage source is ad-justed so that the voltage difference between the supply being measured and the refer-ence voltage will have the required resolution for the measurement being made. Thevoltage difference will be a function of the null detector that is used. Examples of sat-isfactory null detectors are: 419A null detector, a dc coupled oscilloscope utilizingdifferential input, or a 50mV meter movement with a 100 division scale. For the latter,a 2mV change in voltage will result in a meter deflection of four divisions.

5-3


Model No. 6253A, 6284A 6255A, 6269AVariation (mVdc) 6 6Model No. 6281AVariation (mVdc) 5

6294A8

5-17 Line Regulation: To check the line regulation,proceed as follows:

a. Connect variable auto transformer betweeninput power source and power supply power input.

b. Turn CURRENT controls fully clockwise.c. Connect test setup shown in Figure 5-5.d. Adjust variable auto transformer for 105Vac

input.e. Set METER switch to highest voltage

range and turn on supply.f. Adjust VOLTAGE control(s) until front


g. Read and record voltage indicated on dif-ferential voltmeter.

h. Adjust variable auto transformer for 125Vacinput.

i. Reading on differential voltmeter shouldnot vary from reading recorded in step g by morethan the following:Model No. 6253A, 6284A 6255A, 6289AVariation (mVdc) 4 6Model No. 6281A 6294AVariation (mVdc) 2.75 8

Figure 5-5. Load Regulation, Constant VoltageTest Setup

5-18 Ripple and Noise. Ripple and noise measure-ment can be made at any input AC line voltagecombined with any DC output voltage and load currentwithin rating.

5-19 The amount of ripple and noise that is presenton the power supply output is measured either interms of the RMS or (preferably) peak-to-peak value.The peak-to-peak measurement is particularly im-portant for applications where noise spikes couldbe detrimental to a sensitive load, such as logiccircuitry. The RMS measurement is not an idealrepresentation of the noise, since fairly high out-put noise spikes of short duration could be presentin the ripple and not appreciably increase the RMSvalue.

5-20 The technique used to measure high frequencynoise or "spikes" on the output of a power supplyis more critical than the low frequency ripple andnoise measurement technique; therefore the formeris discussed separately in Paragraph 5-28.

Figure 5-6. CV (Constant Voltage)Ripple and Noise Test Setup

5-4


5-21 Ripple and Noise Measurements. Figure 5-6Ashows an incorrect method of measuring p-p ripple.Note that a continuous ground loop exists from thethird wire of the input power cord of the supply tothe third wire of the input power cord of the oscil-loscope via the grounded power supply case, thewire between the negative output terminal of thepower supply and the vertical input of the scope,and the grounded scope case. Any ground currentcirculating in this loop as a result of the differencein potential EG between the two ground pointscauses an IR drop which is in series with the scopeinput. This IR drop, normally having a 60Hz linefrequency fundamental, plus any pickup on the un-shielded leads interconnecting the power supply andscope, appears on the face of the CRT. The magni-tude of this resulting noise signal can easily bemuch greater than the true ripple developed betweenthe plus and minus output terminals of the powersupply, and can completely invalidate the measure-ment.

5-22 The same ground current and pickup problemscan exist if an RMS voltmeter is substituted inplace of the oscilloscope in Figure 5-6. However,the oscilloscope display, unlike the true RMSmeter reading, tells the observer immediatelywhether the fundamental period of the signal dis -played is 8.3 milliseconds (1/120 Hz) or 16.7milliseconds (1/60 Hz). Since the fundamental rip-ple frequency present on the output of an supplyis 120 Hz (due to full-wave rectification), an os-cilloscope display showing a 120 Hz fundamentalcomponent is indicative of a clean measurementsetup, while the presence of a 60 Hz fundamentalusually means that an improved setup will resultin a more accurate (and lower) value of measuredripple.

5-23 Figure 5-6B shows a correct method of mea-suring the output ripple of a constant voltage pow-er supply using a single-ended scope. The groundloop path is broken by floating the supply output.Note that to ensure that no potential differenceexists between the supply and the oscilloscope, itis recommended that whenever possible they bothbe plugged into the same AC power buss. If thesame buss cannot be used, both AC grounds mustbe at earth ground potential.

5-24 Either a twisted pair or (preferably) a shield-ed two-wire cable should be used to connect theoutput terminals of the power supply to the verticalinput terminals of the scope. When using a twist-ed pair, care must be taken that one of the twowires is connected to the grounded input terminalof the oscilloscope. When using shielded two-wire, it is essential for the shield to be connectedto ground at one end only so that no ground current

will flow through this shield, thus inducing anoise signal in the shielded leads.

5-25 To verify that the oscilloscope is not dis-playing ripple that is induced in the leads or pickedup from the grounds, the (+) scope lead should beshorted to the (-) scope lead at the power supplyterminals. The ripple value obtained when theleads are shorted should be subtracted from theactual ripple measurement.

5-26 In most cases, the single-ended scopemethod of Figure 5-6B will be adequate to elimi-nate non-real components of ripple and noise sothat a satisfactory measurement may be obtained.However, in more stubborn cases it may be nec-essary to use a differential scope with floating in-put as shown in Figure 5-6C. If desired, twosingle conductor shielded cables may be substi-tuted in place of the shielded two-wire cable withequal success. Because of its common mode re-jection, a differential oscilloscope displays onlythe difference in signal between its two verticalinput terminals, thus ignoring the effects of anycommon mode signal introduced because of thedifference in the AC potential between the powersupply case and scope case. Before using a dif-ferential input scope in this manner, however, itis imperative that the common mode rejection ca-pability of the scope be verified by shorting to-gether its two input leads at the power supply andobserving the trace on the CRT. If this trace is astraight line, the scope is properly ignoring anycommon mode signal present. If this trace is nota straight line, then the scope is not rejecting theground signal and must be realigned in accordancewith the manufacturers instructions until propercommon mode rejection is attained.

5-27 To check the ripple and noise output, pro-ceed as follows:

a. Connect the oscilloscope or RMS volt-meter as shown in Figures 5-6B or 5-6C.

b. Turn the CURRENT control fully clockwiseand adjust VOLTAGE control until front panel meterindicates maximum rated output voltage.

c. The observed ripple and noise should beless than 200V RMS and 1mV p-p.

5-28 Noise Spike Measurement. When a high fre-quency spike measurement is being made, an in-strument of sufficient bandwidth must be used; anoscilloscope with a bandwidth of 20 MHz or more isadequate. Measuring noise with an instrument thathas insufficient bandwidth may conceal high fre-quency spikes detrimental to the load.

5-29 The test setups illustrated in Figures 5-6A

5-5


and 5-6B are generally not acceptable for measur-ing spikes; a differential oscilloscope is necessary.Furthermore, the measurement concept of Figure5-6C must be modified if accurate spike measure-ment is to be achieved:

1. As shown in Figure 5-7, two coax cables,must be substituted for the shielded two-wire cable.

2. Impedance matching resistors must beincluded to eliminate standing waves and cableringing, and the capacitors must be connected toblock the DC current path.

Figure 5-7. CV Noise Spike Test Setup

3. The length of the test leads outside thecoax is critical and must be kept as short as possi-ble; the blocking capacitor and the impedancematching resister should be connected directly fromthe inner conductor of the cable to the power supplyterminals.

4. Notice that the shields of the power sup-ply end of the two coax cables are not connected tothe power supply ground, since such a connectionwould give rise to a ground current path through thecoax shield, resulting in an erroneous measurement.

5. The measured noise spike values must bedoubled, since the impedance matching resisters,constitute a 2-to-1 attenuator.

6. The noise spikes observed on the oscillo-scope should be less than O.5mV p-p.

5-30 The circuit of Figure 5-7 can also be used forthe normal measurement of low frequency ripple andnoise; simply remove the four terminating resistersand the blocking capacitors and substitute a highergain vertical plug-in in place of the wide-band plug-in required for spike measurements. Notice thatwith these changes, Figure 5-7 becomes a two-cable version of Figure 5-6C.

5-31 Transient Recovery Time. To check thetransient recovery time proceed as follows:

a. Connect test setup shown in Figure 5-8.b. Turn CURRENT controls fully clockwise.c. Set METER switch to highest current



e. Close line switch on repetitive loadswitch setup.

f. Adjust 25K potentiometer until a stabledisplay is obtained on oscilloscope. Waveformshould be within the tolerances shown in Figure5-9 (output should return to within 15mV of originalvalue in less than 50 microseconds).

Figure 5-8. Transient Response, Test Setup

Figure 5-9. Transient Response, Waveforms

5-6


5-32 Proqramming Speed. This measurement ismade by monitoring the output voltage with an os-cilloscope while rapidly changing the remote pro-gramming resistance. For up-programming, the re-mote resistance is varied from zero ohms to the val-ue that will produce maximum output voltage; andfor down-programming, the remote resistance is var-ied from the value that will produce maximum outputvoltage to zero ohms. To check the up-programmingspeed, make the connections indicated in Figure5-10; for down-programming, simply remove RL.

Figure 5-10. CV Programming Speed, TestSetup

The load resistance is included for up-programmingand removed for down-programming to present theworst possible conditions for the supply to reachthe programmed voltage. Refer to Application Note90, Power Supply Handbook for further details onremote programming speed. To check the program-ming speed, proceed as follows:

1. Restrap the rear barrier strip as indicatedin Figure 5-10. Note that the jumper between +Sand A10 is removed. This disconnects the outputcapacitor C20 to increase the programming speed.A minimum amount of output capacitance (C19) ispermanently wired to the output and should not beremoved, because the supply could oscillate undercertain load conditions. The programming speed in-creases by a factor of from 10 to 100 when the out-put capacitor C20 is removed.

2. Connect the relay, oscilloscope, and pro-gramming resistor Rp as illustrated in Figure 5-10.Select the value of the programming resister that

will produce maximum output voltage of the supply.This val

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HP6255A Service Manual