thermal equivalent circuit for a transistor. junction temperature case temperatureheat sink...
Post on 15-Jan-2016
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Thermal Equivalent Circuit for a Transistor
Junction Temperature
Case Temperature Heat Sink Temperature
Ambient Temperature
Thermal Resistance from Junction to Case
Thermal Resistance from Case to Heat Sink
Thermal Resistance from Heat Sink to Ambient
Total Average Power Loss
( )
C J T J C
S C T CS
A S T SA
J A T J C CS SA
T T P R
T T P R
T T P R
T T P R R R
Motorola MS-10 Heat Sink
Performance Under Forced Air Flow
Thermal Characteristic in Free Air
Top View of MS-10 Heat Sink
Hole Pattern for a TO-3 Case
Mica Insulator
Thermal Resistances for Mica Insulators
Clip-On Heat Sinks
Thermal Performance
Thermal Resistance for Clip-On
Bond-On Extrusions for DIP Packages
Thermal Performance
Thermal Resistances for Bond-On
Example
• TO-220 case style dissipating 5 watts
• RJC = 3.0 C / Watt (from device spec)
• TJmax = 150 C
• TAmax = 50 C
• Find the proper heat sink to keep the junction temperature from exceeding 150C in natural convection.
Need to determine a value for RCS – depends on the mounting technique.
If the device is mounted without an insulator, but only with Thermalcote, (silicone grease), check page 57, Figure 9 for TO -220 case style.
( )
J A
D
J C CS SA
J A
SA J C CS
D
T TP
R R RT T
R R RP
RCS = 1 C/W
No Insulator
Use Thermalcote
( )
(150 50 )(3 1)
5
16
J A
SA J C CS
D
SA
SA
T TR R R
P
C CR
W WC
RW
Thermalloy P/N 6030
Temperature rise above ambient@ 5 Watts Power Dissipation = 66 C
Thermal Resistance RSA
6613.2
5SA
C CR
W W
As long as RSA is less than 16 C/W, the requirement is met.
Thermalloy P/N 6030