dear sir,
when i am applying a gate signal to the npn ibgt the led is on, which is connected between emitter & collector.
If i removed gate supply to igbt still the led is glowing.
what is the reason ?

 

Probably some residual gate charge on the IGBT. Put a 10k resistor from the gate of the IGBT to ground.

Always show your circuit if you have questions.

 

Thanks for the reply
I got the answer,even though the source is open circuited ,the igbt will have some internal capacitance. since it is not short circuited it will discharge through led.