Dim LED with Transistor Switch - Why?

[brodywx]

Hello,

I've just been playing around with a 2n3904 transistor and 3V coin battery. I noticed when powering an LED with a transistor switch the LED is significantly dimmer than when powering the LED directly.

Why is this? Is it because 0.7 volts is siphoned off just to turn the transistor on?

 

[yungman]

The saturation voltage. Even if you drive the base hard, their is a 0.3V drop across the CE of the transistor so only get 2.7V instead of 3V. If you want to get rid of this, get a MOSFET with low rds.

 

[brodywx]

Thank you for the reply.

I
am
learning