Thermal Equivalent Circuit for a Transistor ECE 442
- Slides: 25
Thermal Equivalent Circuit for a Transistor ECE 442 1
Case Temperature Heat Sink Temperature Junction Temperature Ambient Temperature ECE 442 2
Thermal Resistance from Junction to Case Total Average Power Loss Thermal Resistance from Case to Heat Sink Thermal Resistance from Heat Sink to Ambient ECE 442 3
ECE 442 4
Motorola MS-10 Heat Sink ECE 442 5
Performance Under Forced Air Flow ECE 442 6
Thermal Characteristic in Free Air ECE 442 7
Top View of MS-10 Heat Sink ECE 442 8
Hole Pattern for a TO-3 Case ECE 442 9
Mica Insulator ECE 442 10
Thermal Resistances for Mica Insulators ECE 442 11
ECE 442 12
Clip-On Heat Sinks ECE 442 13
Thermal Performance ECE 442 14
Thermal Resistance for Clip-On ECE 442 15
Bond-On Extrusions for DIP Packages ECE 442 16
Thermal Performance ECE 442 17
Thermal Resistances for Bond-On ECE 442 18
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 150 C in natural convection. ECE 442 19
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. ECE 442 20
Use Thermalcote RCS = 1 C/W ECE 442 21 No Insulator
ECE 442 22
Thermalloy P/N 6030 Temperature rise above ambient@ 5 Watts Power Dissipation = 66 C ECE 442 23
Thermal Resistance RSA As long as RSA is less than 16 C/W, the requirement is met. ECE 442 24
Thermalloy P/N 6030 ECE 442 25
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- Ece 442 çankaya
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