Simple BJT Question

Thread Starter


Joined Oct 23, 2004
Hey guys,

For a NPN BJT, I know that in order to be running in the Forward Active Region ,we have to forward bias the Base-Emitter Junction, and Reverse Bias the Base Collector Junction

my question is as follows

does that mean the voltage at the base just has to be higher than that of the emitter ? or does it have to be higher that 0.7 across?

what about the Base collector? does the collector voltage have to be higher than the base ? or higher by 0.7 ?

thanks guys


Joined Dec 27, 2007
I think you answered your own question.. You want to forward bias the base-emitter, then you need to ensure the voltage differential is at least 0.7V for a standard BJT. This means that if the emitter is 10V, then the base must be at least 0.7V. The same goes for the collector-emitter junction.



Joined Dec 20, 2007
The base to emitter is a silicon diode. The diode's voltage is 0.6V at very low current, 0.7V at medium current and up to 1.5V at high current. The base voltage for a turned on NPN transistor is more positive than the emitter voltage.

The collector voltage drops lower than the base voltage when an NPN transistor is saturated. Then some current flows from base to collector.