Why the LED stays on for some time ?

[joseche]

Hi all,

I was doing my second circuit, first one with a transistor !

But I didn't get the result I wanted, instead I got a surprise I don't understand.

My idea was to put a delay on the LED, so it will not turn on immediately after I plug the battery, instead I got the opposite, it takes a while to turn off, I can unplug the battery and the light diminishes slowly ( 1 minute approx. )

I don't understand how the led can emit light if the circuit is not closed !?!?

Is it because the capacitor -> transistor -> led -> capacitor is a closed circuit even when the transistor is not receiving nothing on the emitter ?, it means there is a flow from the base to the collector ??

Thanks

 

[cobra1]

when the battery is connected, it will charge up the capacitor, and the led will be lit. when the battery is disconnected, the capacitor temporarily takes the place of the battery and continues to light the led for a short time.

 

[Boncuk]

Hi joseche,

you might want to play with this and find the answers yourself.

Boncuk