# ECE 442 Power Electronics1 Two Devices on a Common Heat Sink Thermal Model.

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ECE 442 Power Electronics1 Two Devices on a Common Heat Sink Thermal Model

ECE 442 Power Electronics2

3 The heat sink Thermal Resistance

ECE 442 Power Electronics4 If the two devices are identical The heat sink needs to have half of the thermal resistance required for one device alone. If the devices are not identical, the required thermal resistance is the smaller of the two previously computed values.

ECE 442 Power Electronics5 Example Specify a heat sink for two identical power devices with a maximum junction temperature of 150 C to operate in an ambient temperature of 50 C. The power dissipation in each device is 20W and the junction-to-case thermal resistance is 1.5 C/W. The thermal resistance of the mica insulators is 0.5 C/W.

ECE 442 Power Electronics6 One device would require R SA = 3.0 C/W

ECE 442 Power Electronics7 Check the Junction Temperature Device #1

ECE 442 Power Electronics8 For N devices with Common Heat Sink For the nth device

ECE 442 Power Electronics9 For n Identical Devices

ECE 442 Power Electronics10 Example Repeat the previous example if there are three identical devices that dissipate 10W each.

ECE 442 Power Electronics11

ECE 442 Power Electronics12 Check the Junction Temperature Device #1

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