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Thermal Equivalent Circuit for a Transistor

Thermal Equivalent Circuit for a Transistor. Case Temperature. Heat Sink Temperature. Junction Temperature. Ambient Temperature. Thermal Resistance from Junction to Case. Thermal Resistance from Case to Heat Sink. Total Average Power Loss.

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Thermal Equivalent Circuit for a Transistor

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  1. Thermal Equivalent Circuit for a Transistor

  2. Case Temperature Heat Sink Temperature Junction Temperature Ambient Temperature

  3. Thermal Resistance from Junction to Case Thermal Resistance from Case to Heat Sink Total Average Power Loss Thermal Resistance from Heat Sink to Ambient

  4. Motorola MS-10 Heat Sink

  5. Performance Under Forced Air Flow

  6. Thermal Characteristic in Free Air

  7. Top View of MS-10 Heat Sink

  8. Hole Pattern for a TO-3 Case

  9. Mica Insulator

  10. Thermal Resistances for Mica Insulators

  11. Clip-On Heat Sinks

  12. Thermal Performance

  13. Thermal Resistance for Clip-On

  14. Bond-On Extrusions for DIP Packages

  15. Thermal Performance

  16. Thermal Resistances for Bond-On

  17. 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.

  18. 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.

  19. Use Thermalcote RCS = 1 C/W No Insulator

  20. Thermalloy P/N 6030 Temperature rise above ambient@ 5 Watts Power Dissipation = 66 C

  21. Thermal Resistance RSA As long as RSA is less than 16 C/W, the requirement is met.

  22. Thermalloy P/N 6030

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