A silicon transistor with β = 120 is connected to a supply of 12 V…

Contributed by StemPy Lab

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A silicon transistor with $\beta = 120$ is connected to a supply of $12$ V. A resistor of $470\ \text{k}\Omega$ joins the supply to the base, and a resistor of $2.2\ \text{k}\Omega$ joins the supply to the collector. The emitter is grounded. Find the base current, the collector current and the collector-emitter voltage. Say which region the transistor is in.

Need a reminder? The key ideaShow

In a transistor, $I_E = I_B + I_C$ , $\alpha = \dfrac{I_C}{I_E}$ and $\beta = \dfrac{I_C}{I_B}$ , with $\beta = \dfrac{\alpha}{1 - \alpha}$ . In the common-emitter circuit, $V_{BB} = I_B R_B + V_{BE}$ and $V_{CC} = I_C R_C + V_{CE}$ , with $V_{BE} = 0.7$ V for silicon. The input resistance is $r_i = \left(\dfrac{\Delta V_{BE}}{\Delta I_B}\right)_{V_{CE}}$ and the output resistance is $r_o = \left(\dfrac{\Delta V_{CE}}{\Delta I_C}\right)_{I_B}$ .

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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