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1
Final Control
• Introduction• Thermal Circuits
–Thermal resistance–Heat Sinks–2N3904 example–OPA512 example
•JFET/MOSFET Review•Summary
2
Types of Heat Sinks
http://www.wakefield.com/
Ball Grid Array
For:IntelAMDPowerPC
SurfaceMount,WaveSolderable,Snap-down
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System Parameters
Type of System
Parameter
Quantity Potential Time
Electrical Charge EMF or Voltage
Second
Liquid Volume Pressure Second
Gas Mass Pressure Second
Thermal Heat Temperature Second
Mechanical Distance Force Second
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Defining Resistance
Type of System Change in Quantity Parameter
Description Name (SI Units)
Electrical Charge xfrd.
per sec.
Current (amperes)
Liquid Volume
Xfrd. per sec.
Flow Rate (Cubic meters per second)
Gas Gas xfrd.
per sec.
Flow Rate (kilograms per second)
Thermal Heat xfrd.
per sec.
Flow rate of energy (joules per second)
Mechanical Distance
per sec.
Velocity (meters per second)
dt
dq
dt
dV
dt
dmass
dt
dW
dt
dx
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Thermal Definitions
Rθ
TJ
TA
TC
RθJC
RθCA
T= TJ -TA
J = junctionC=caseA=ambient
PD = power dissipated
PD
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A simple thermal circuit
PD = 120 mW =.12 W
TJ
TA
RθJA = 2000C/W
T = 240 C = TJ – TA = PD*RθJA
TJ(max) = 1500CMax power:
BJT ~ PCE
FET ~ PDS
SCR ~ PAK
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A complete thermal circuit with heat sink
PD
TJ
TC
TA
TS
RθJC
RθCS
RθSA
RθJC = Thermal Resistance from Junction to Case
T
RθSA = Thermal Resistance from Case to ambientRθCS = Thermal Resistance from Case to sink
T
http://www.electronics-cooling.com/Resources/EC_Articles/JUN95/jun95_01.htm
8Common Cases
http://sound.westhost.com/heatsinks.htm#introduction
9Mounting a heat sink
http://www.gensemi.com/launch/ITO-220Rectifiers-external.ppt
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Mounting a TO-3 Heat Sink
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2N3904 BJT
Specs
http://www.onsemi.com/pub/Collateral/2N3903-D.PDF
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BJT Amplifier Circuit: Spec
says max. ambient
temperature will be 1200C
Example 1: RθJA for the 2N3904 is 200 0C/W,
VC = 10 volts
VE = 1.05 volts
VCE = 9 volts
PD = 9*20 = 180 mWPD = 180 mW =.18 W
TJ
TA
RθJA
T = 360C = TJ – TA = PD*RθJA
TJ(max) = 1500C
TO-92 Style Case
13Adding a heat sink
TO-92 Heat Sink
From Digikey: RθSA= 640C per Watt
PD
TJ
TC
TA
TS
RθJC
RθCS
RθSA
T
From 2N3904 spec: RθJC= 83.30C per Watt
From general: RθCS= 50C per Watt
RθTotal = 148.30C/WattT = TJ-TA = 26.70C
PD = 180 mW =.18 W
TJ(max) = 1500C
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OPA 512
http://focus.ti.com/docs/prod/productfolder.jhtml?genericPartNumber=OPA512
Absolute MaxInternal powerDissipation =125 Watts
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OPA512 Problem
• OPA512, 125W, 15A
• RθJA = 30 0C/ Watt
• RθJC = .9 0C/ Watt
PD = 9*20 = 180 mWTJ
TA
RθJA
PD = (TJ – TA)/RθJA=
110/30 = 3.67Watts
TJ(max) = 1500C TA= 400C
Need 30 watt AC amplifierfor an audio application. Themax temp will be 1040F
First look at no heat sink:
http://www-s.ti.com/sc/ds/opa512.pdf
TJ
TC
TA
TS
RθJC=.9
RθCS
RθSA
T
30 = (TJ – TA)/RT=110/RT
RT = 3.67 0C/Watt total
So RθCS+RθSA=3.67-.9=2.77
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TO3 Mounting Kit
Mounting a TO-3 Heat Sink
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Pentium 4 Heat Sinkhttp://www.aavidthermalloy.com/products/microp/desktop.shtml#Pentium%20IV
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Athlon Heat Sinkhttp://www.aavidthermalloy.com/products/microp/desktop.shtml#AMD%20Processors
http://www.aavidthermalloy.com/technical/index.shtml
http://www.electronics-cooling.com/Resources/EC_Articles/JUN95/jun95_01.htm
19
Power Derating Curve150 0C
5 W
25 0C
5W125
= 25 0C/WattRθJC=
21IRL630 HEXFET Switching Power MOSFET
http://www.irf.com/product-info/datasheets/data/irl640s.pdf
RθJC= 1.7 0C/Watt (max) RθCS= .50C/Watt (flat, greased surface)
RθJA= 62 0C/Watt (max)
22Another Heat Sink Problem
RθJC= 1.7 0C/Watt (max)
RθCS= .50C/Watt (flat, greased surface)RθJA= 62 0C/Watt (max)
Max continuous drain current = 9 ampsRds = .4ΩMax power dissipated = 74 W @ 250CLinear derating factor = .59 W/0C
62125
= 2.02 WPD=150 0C
25 0C
PD
TTJ
TC
TA
TS
RθJC=1.7
RθCS=.5
RθSA
T
So the max power that can be dissipated is: RθJC+RθCS+RθSA=1.7+.5+4=6.20C/W and
PD=125/6.2=20.2W
Best TO-220 at Digikey is:RθSA=4 0C/W
23
CMOS: Complementary Metal-Oxide Semiconductor
CMOS is a widely used type of semiconductor. CMOS semiconductors use both NMOS (negative polarity) and PMOS (positive polarity) circuits. Since only one of the circuit types is on at any given time, CMOS chips require less power than chips using just one type of transistor.
http://tech-www.informatik.uni-hamburg.de/applets/cmos/cmosdemo.html
http://www.webopedia.com/TERM/C/CMOS.html
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Summary• Thermal Circuits
– Thermal resistance– Heat Sinks– 2N3904 example– OPA512 example
• JFET/MOSFET Review– IRL630 Heat Sink example
• Next– Industrial Electronics
•SCR•TRIAC•DIAC
–Stepping Motors
