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Why does a transistor heat when base current is high


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i tried many transistors like sl 100,bc 548 etc in these the base is connected to voltage source through a high value resistor (some 1 kilo ohm) when i tried to decrease the value of resistor,output current to load decreased and transistor temperature increased.why transistor temperature increased & output current decreased when i decreased the value of resistor.

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Hi alivol,
              I tried to use transistor as a switch,also i dont know how to make a schematic picture.i just experimented with transistor,resistor and a relay.

Hi indulis,
              You are currect,emitter current is high which is essential to switch on the relay,i want to know the theory behind this heating


              Thanks to everyone who replied & read my post.

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The relay coil is an inductor. An inductor creates a very high voltage when its current is stopped, the voltage can destroy its driving transistor unless a diode is connected across the relay's coil in reverse to arrest the voltage spike.

Heating is caused by the voltage across the transistor multiplied by the current through it. Relays are available that use a fairly low coil voltage and current. Then when the driving transistor is turned on, its base current is very low, its load current is low and the voltage across it is very low so it doesn't heat.

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