princestephenranji Posted June 3, 2006 Report Share Posted June 3, 2006 Why does a transistor heat when base current is high Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 4, 2006 Report Share Posted June 4, 2006 Why does a transistor heat when base current is highWhich transistor?Why is the base current high?What amount is the base current?What amount is the collector current?Why doesn't the transistor have an adequate heatsink? Quote Link to comment Share on other sites More sharing options...
princestephenranji Posted June 4, 2006 Author Report Share Posted June 4, 2006 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. Quote Link to comment Share on other sites More sharing options...
allvol Posted June 4, 2006 Report Share Posted June 4, 2006 Hello, princeHow are you using your transistor? Quote Link to comment Share on other sites More sharing options...
indulis Posted June 4, 2006 Report Share Posted June 4, 2006 Two reasons come to mind right away.........1) base current isn't being limited2) you have a high emitter current with a high Vce Quote Link to comment Share on other sites More sharing options...
princestephenranji Posted June 4, 2006 Author Report Share Posted June 4, 2006 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. Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 4, 2006 Report Share Posted June 4, 2006 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. Quote Link to comment Share on other sites More sharing options...
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