(a) State THREE sources of losses in power semiconductor devices. [3] (b) Draw the electrical equivalent circuit for the thermal process of cooling power semiconductor devices using heat sinks. Explain the meaning of each parameters used in [6] the circuit. (c) A power transistor switches a 100V, 20A inductive load at 10 kHz. The transistor maximum on-state duty cycle

 

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(a) State THREE sources of losses in power semiconductor devices. [3] (b) Draw the electrical equivalent circuit for the thermal process of cooling power semiconductor devices using heat sinks. Explain the meaning of each parameters used in [6] the circuit. (c) A power transistor switches a 100V, 20A inductive load at 10 kHz. The transistor maximum on-state duty cycle is 90% and has a junction-to-case thermal resistance of 0.7°C/W. The transistor on-state voltage is clamped to IV and the switch-on and switch- off times are 1 us and 2 us respectively: (i) Determine the total power loss. The power loss for switching inductive load is given by: Ps= Tfs Where V, is the maximum voltage, I is the maximum current, r is the switching time, and f. is the switching frequency. [5] (ii) If the junction temperature is not to exceed 125°C with an ambient temperature of 35 °C, determine the required heat sink thermal resistance. [5] (d) Discuss TWO factors that minimize the thermal resistance between the case of a power semiconductor device and a beatsink. [6]

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