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Diodes. Impurity Atoms: Trivalent : Boron (B), Aluminum (Al), Gallium (Ga), Indium (ln). Has three (3) valence electrons. Known as an “Acceptor Impurity.” Pentavalent : Phosphorous (P), Arsenic (As), Antimony (Sb), and Bismuth (Bi). Has five (5) valence electrons. - PowerPoint PPT Presentation
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CENT-112 Fundamentals of Electricity and Electronics1
Impurity Atoms:•Trivalent: Boron (B), Aluminum (Al), Gallium (Ga), Indium (ln). Has three (3) valence electrons.
–Known as an “Acceptor Impurity.”•Pentavalent: Phosphorous (P), Arsenic (As), Antimony (Sb), and Bismuth (Bi). Has five (5) valence electrons.
–Known as a “Donor Impurity.”
Diodes
CENT-112 Fundamentals of Electricity and Electronics2
–“N - Type” Material:•Pure base material doped with a Donor Impurity.•Majority Current Carrier: Electrons•Minority Current Carrier: Holes
–“P - Type” Material:•Pure base material doped with an Acceptor Impurity.•Majority Current Carrier: Holes•Minority Current Carrier: Electrons
PN Material
CENT-112 Fundamentals of Electricity and Electronics3
–Old Method: Grown Crystals.
–Newer Methods:
•Alloy Fused: N & P material made using heat / pressure.
•Diffused: N & P gas and heat.
–Both methods are used to produce a “PN” Junction.
Construction
CENT-112 Fundamentals of Electricity and Electronics4
Questions
Q) What is meant by a donor impurity?
A) 5 valiant electrons in outer shell.
Q) What are 4 examples of a donor impurity?
A) Phosphorous, Arsenic, Antimony and Bismuth.
CENT-112 Fundamentals of Electricity and Electronics5
• Potential Hill (Junction Barrier) : Electrostatic field set up across a PN junction which prevents further combination of majority current carriers.
• The value of the voltage of the potential hill depends on the type of base material used during diode construction.
1. Silicon (.5 - .8V)
2. Germanium (.2V)• Rated for up to 1500A / 3000V.• Used primarily in Rectifiers.
Diode Definitions
CENT-112 Fundamentals of Electricity and Electronics6
Operations & Definitions
•Forward Bias: External voltage applied which opposes the potential hill, effectively reducing the width and resistance of the depletion region. => Majority Current Carriers flow through the PN junction.
•Reverse Bias: External voltage applied which aids the potential hill, effectively increasing the width and resistance of the depletion region. => No Majority Current Carriers flow through the PN junction.
CENT-112 Fundamentals of Electricity and Electronics7
Rectifier Diode Block Diagram
+ + +
+ P +
+ + +
Anode Cathode
Potential Hill (Junction Barrier)
Depletion Region
- - -
- N -
- - -
- -
- -
- -
- -
+ +
+ +
+ +
+ +
CENT-112 Fundamentals of Electricity and Electronics8
Rectifier Diode Schematic Diagram
Anode Cathode
CENT-112 Fundamentals of Electricity and Electronics9
Diode Forward Bias
+ + +
+ P +
+ + +
Anode Cathode
Potential Hill (Junction Barrier)
Depletion Region
- - -
- N -
- - -
-
-
-
-
+
+
+
+ + -
CENT-112 Fundamentals of Electricity and Electronics10
Diode Reverse Bias
+ + +
+ P +
+ + +
Anode Cathode
Potential Hill (Junction Barrier)
Depletion Region
- - -
- N -
- - -
- - -
- - -
- - -
- - -
+ + +
+ + +
+ + +
+ + + +-
CENT-112 Fundamentals of Electricity and Electronics11
Characteristic Curve
+I (mA)
Forward Bias
Reverse Bias
-I (uA)Avalanche Breakdown
+V a -c-V a -c
CENT-112 Fundamentals of Electricity and Electronics12
Zener Diode
–The Zener diode is a heavily doped diode which, as a result of doping, has a very narrow depletion region. This allows the diode to be operated in the reverse biased region of the characteristic curve without damaging the PN junction.
–“Zener Effect”: The area of Zener diode operation (<5V) where the Diode maintains a constant voltage output while operating reverse biased.
–“Avalanche Effect”: >5V applied to the diode while reverse biased which tends to cause the diode to eventually breakdown due to heat generation within the lattice structure of the crystal.
CENT-112 Fundamentals of Electricity and Electronics14
Characteristic Curve
Operating Region
Reverse Bias
Forward Bias
+ V a - c- V a - c
I (mA)
I (uA)
CENT-112 Fundamentals of Electricity and Electronics15
Zener Operation
•Ratings: .25V to 1500V
•Used in SSMG / SSTG AC voltage regulator for the reference circuit.
When a higher constant voltage is desired, the zener diodes will be “Stacked” together in series and their voltages will add together to make the higher desired voltage.
This is the case in the SSMG / SSTG AC voltage regulators where four (4) 6v zener diodes are stacked to provide a 24V reference to the comparison circuit.
CENT-112 Fundamentals of Electricity and Electronics16
Zener Diode Voltage Regulator
R1
CR1
Vin Vout
CENT-112 Fundamentals of Electricity and Electronics17
Signal Diode
•Same construction as the Rectifier Diode except that it is designed to operate with a very short “reverse recovery time” to allow it to rectify high frequency AC inputs.
CENT-112 Fundamentals of Electricity and Electronics18
Power Supplies
•Components and their function–Transformer - Receives the AC input from the distribution system and either steps up or down the voltage.–Rectifier - Converts the AC input voltage from the transformer to a pulsating DC voltage.–Filter - Smoothes out the DC pulsations or ripple received from the rectifier.–Regulator - Receives a smoothed DC voltage from the Filter Stage and produces a steady DC voltage to be used by electronic circuitry.
CENT-112 Fundamentals of Electricity and Electronics19
Half - Wave Rectifier
VOUTVIN
1 : 1
T1
CR1
R1
CENT-112 Fundamentals of Electricity and Electronics20
• Positive half-cycle the diode is Forward Bias (FB), negative half-cycle the diode is Reverse Bias (RB).
Half - Wave Rectifier Operation
VDC = VPK X .318Where: VDC = Average DC voltage
VPK = Peak input voltage
.318 = Constant
CENT-112 Fundamentals of Electricity and Electronics21
Full - Wave Rectifier
VOUTVIN
1 : 1
T1
CR1
R1
CR2
CENT-112 Fundamentals of Electricity and Electronics22
• Positive half-cycle, 1 diode is FB, negative half-cycle the other diode is FB.
Full - Wave Rectifier Operation
VDC = VPK X .637Where: VDC = Average DC voltage
VPK = Peak input voltage
.637 = Constant
CENT-112 Fundamentals of Electricity and Electronics23
Full – Wave Bridge Rectifier
VOUTVIN
1 : 1
T1
CR1
R1
CR2
CR3CR4
CENT-112 Fundamentals of Electricity and Electronics24
• Positive half-cycle, 1 diode is FB, negative half-cycle the other diode is FB.
Full - Wave Bridge Rectifier Operation
VDC = VPK X .637Where: VDC = Average DC voltage
VPK = Peak input voltage
.637 = Constant
CENT-112 Fundamentals of Electricity and Electronics25
Filters
•A filter uses the characteristics of Inductors and Capacitors to smooth the pulsating DC waveform supplied by the Rectifier.
–Types•High Pass - A series RC filter whose output is taken from the resistor.
•Series / Parallel - A filter configuration which uses combinations of capacitors and inductors to smooth the voltage and current pulsations from the rectifier output.
CENT-112 Fundamentals of Electricity and Electronics26
• Rapid charge time constant for filter capacitors and inductors.
• Slow discharge time constant for filter capacitors and inductors.
Ideal filter characteristics
CENT-112 Fundamentals of Electricity and Electronics27
Capacitor Filter Configuration
RB
C1
VIN VOUT
•Capacitor Input Filter Schematic Diagram
CENT-112 Fundamentals of Electricity and Electronics28
Capacitor Filter Operation
•Charge RC time constant is developed from the internal resistance of the rectifier diodes and the capacitance of the filter capacitor. The net result is that the low resistance of the rectifier diodes develop a rapid charge RC time constant.
•Discharge RC time constant is developed from the filter capacitor and the load resistance. Since the load resistance is rather large, the discharge RC time constant is somewhat long.
•RB is called the “Bleeder Resistor” because it provides a path for the filter capacitor(s) to discharge when power is removed from the circuit. RB has a very large resistance and usually draws <10% of normal operating current.
CENT-112 Fundamentals of Electricity and Electronics29
LC Choke Filter Configuration
•LC Choke Filter Schematic Diagram
RB
C1
VIN VOUT
L1
CENT-112 Fundamentals of Electricity and Electronics30
LC Choke Filter Operation
•Charge RC time constant is developed from the internal resistance of the rectifier diodes, the Low DC resistance of the inductor (L1), and the capacitance of the filter capacitor. The net result is that the low resistance of the rectifier diodes and inductor (L1) develop a rapid charge RC time constant.
•Discharge RC time constant is developed from the filter capacitor and the load resistance. Since the load resistance is rather large, the discharge RC time constant is somewhat long.
•The Inductor acts to smooth out the current pulsations produced by the rectifier and / or transformer stage of the power supply.
CENT-112 Fundamentals of Electricity and Electronics31
RC PI Filter Configuration
•RC PI Filter Schematic Diagram
RB
C2
VIN VOUTC1
R1
VOUT(C1)
VOUT (C2)
Charge Path
Discharge Path
CENT-112 Fundamentals of Electricity and Electronics32
RC PI Filter Operation
•First Capacitor provides most of the filtering action.•Second Capacitor Provides additional voltage filtering.•Resistor limits current flow to the desired value and establishes the RC time constants for both filter capacitors.
CENT-112 Fundamentals of Electricity and Electronics33
LC PI Filter Configuration
•LC PI Filter Schematic Diagram
RB
C2
VINC1
L1
VOUT(C1)
VOUT (C2)
Charge Path
Discharge Path
CENT-112 Fundamentals of Electricity and Electronics34
LC PI Filter Operation
•First Capacitor provides most of the filtering action.•Second Capacitor Provides additional voltage filtering.
•Inductor opposes changes in current flow to reduce current spikes and establishes the RC time constants for both filter capacitors.
CENT-112 Fundamentals of Electricity and Electronics35
Voltage Regulators
R1
CR1
Vin Vout
–Series Regulator•Acts as a variable resistor in series with the load.
–Zener Diode Voltage Regulator•Schematic
CENT-112 Fundamentals of Electricity and Electronics36
Voltage Regulator Operation
R1CR1
Vin Vout
VIN
VOUT