a) A thyristor in a fully-controlled converter that supplies 66yA to a D.C. load is mounted on a0.5 kg aluminium heat sink. If the forward voltage across the device is

1.5 V, and aluminium has a specific heat capacity of 895 J(kg °C)-1. The ambient temperature is 40 °C maximum and the thyrist or is mounted directly on the heat sink. (i) Calculate the steady state temperature of the thyrist or junction, given that the thermal resistance of the heat sink is 0.15 °C W-1 and that of the device is 0.12°CW-1. (ii) How long does the heat sink take to reach a steady-state temperature? b) Draw a circuit with two transistors, a PNP and NPN, and then determine and prove a formula for la in terms of common base gains. Explain how the circuit operates. c) State an electronic power component and explain how heat dissipation can be modelled.