Thermal Equivalent Circuit for a Transistor ECE 442

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Thermal Equivalent Circuit for a Transistor ECE 442 1

Thermal Equivalent Circuit for a Transistor ECE 442 1

Case Temperature Heat Sink Temperature Junction Temperature Ambient Temperature ECE 442 2

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

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

ECE 442 4

Motorola MS-10 Heat Sink ECE 442 5

Motorola MS-10 Heat Sink ECE 442 5

Performance Under Forced Air Flow ECE 442 6

Performance Under Forced Air Flow ECE 442 6

Thermal Characteristic in Free Air ECE 442 7

Thermal Characteristic in Free Air ECE 442 7

Top View of MS-10 Heat Sink ECE 442 8

Top View of MS-10 Heat Sink ECE 442 8

Hole Pattern for a TO-3 Case ECE 442 9

Hole Pattern for a TO-3 Case ECE 442 9

Mica Insulator ECE 442 10

Mica Insulator ECE 442 10

Thermal Resistances for Mica Insulators ECE 442 11

Thermal Resistances for Mica Insulators ECE 442 11

ECE 442 12

ECE 442 12

Clip-On Heat Sinks ECE 442 13

Clip-On Heat Sinks ECE 442 13

Thermal Performance ECE 442 14

Thermal Performance ECE 442 14

Thermal Resistance for Clip-On ECE 442 15

Thermal Resistance for Clip-On ECE 442 15

Bond-On Extrusions for DIP Packages ECE 442 16

Bond-On Extrusions for DIP Packages ECE 442 16

Thermal Performance ECE 442 17

Thermal Performance ECE 442 17

Thermal Resistances for Bond-On ECE 442 18

Thermal Resistances for Bond-On ECE 442 18

Example • • • TO-220 case style dissipating 5 watts RJC = 3. 0

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

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

Use Thermalcote RCS = 1 C/W ECE 442 21 No Insulator

ECE 442 22

ECE 442 22

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

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

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

Thermalloy P/N 6030 ECE 442 25