Next Report - Application circuits for BJTs

Jony130

Joined Feb 17, 2009
5,488
First let's assume that BJT is in active region for R_load = 2.2k.
This means that Ie = 4mA and Ve = 4V. Now let's try to find Vc voltage.
Vc = Vcc - Ic*Rc ≈ 3.24V and Vce = Vc - Ve = 3.24V - 4V = -0.76V

So we get negative Vce value, but negative value is impossible to get in this circuit . And this means that our BJT is indeed in saturation region. And in saturation region Ic = β*Ib don't hold anymore. In saturation we can only rely on this Ie = Ib + Ic and basic electronics laws. Also we are forced to assume some Vce_sat value.
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,759
First let's assume that BJT is in active region for R_load = 2.2k.
This means that Ie = 4mA and Ve = 4V. Now let's try to find Vc voltage.
Vc = Vcc - Ic*Rc ≈ 3.24V and Vce = Vc - Ve = 3.24V - 4V = -0.76V

So we get negative Vce value, but negative value is impossible to get in this circuit . And this means that our BJT is indeed in saturation region. And in saturation region Ic = β*Ib don't hold anymore. In saturation we can only rely on this Ie = Ib + Ic and basic electronics laws. Also we are forced to assume some Vce_sat value.
Ok, let me just ask where is Vc in the circuit? I got confused now!
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,759
Ok, thanks for everything.

This job is almost done. My next one will be about mosfets...

I will start a new thread maybe tomorrow!
 
Top