at room temp a power transistor has beta of 160 and it is used in a DC dimmer ci

Question

at room temp a power transistor has beta of 160 and it is used in a DC dimmer circuit to control a 24 volt 120 watt lamp the lamp power supply is 48 volts dc and it can deliver a maximum of 21 amperes of current A)Sketch diagram of lamp at 100 percent brigthnesss B)calculate lamp current of 100 percent brightness C)find base current of transistor D)how much power is dissipated by the transistor E)what happens when the transistor heats up F)if the transistor shorts out between the collector and the emitter what happens to the lamp G)can the lamp be protected

Explanation / Answer

b).Lamp current at 100% brightness=>P=V*I=>120/24=I=>I=5A where P=Power of lamp,V=voltage of dimmer circuit; c)Ic=ßIb=>5=160Ib=>Ib=31mA; d)P=V*I=>V=0.7 and I=31mA=>P=0.021875 Watts; e)When transistor heats up its beta value increases resulting an increase in power dissipation across it f)Lamp gets burned out due to excessive power dissipation across it and high current g)Yes lamp can be protected by using a shunt resistor across it

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