Question

A transistor in a common Emitter configuration is used as a switch, and it is in the ON position. Find the output voltage $V_{out}$.

Answer 1

1. This is the diagram of the transistor in common emitter mode.
2. In the switch ON case transistor is in saturation mode.
3. Maximum collector current flows ($I_c=\frac{V_{cc}}{R_L}$ ).
4. $V_{CE}=0$ ( ideal saturation ). Transistor operates as a “closed switch”
5. In the cutoff region the transistor is fully off.
6. From the diagram on the right side we can see that $V_{out}$ is connected to earth.
7. $V_{out}=V_{CE}=0$
8. So, $V_{out}$ is equal to zero.

Hence, $V_{out}=0$.