I have this task: When Vb changes, shall Vc change -4 time as much. Can you deside Re so this will happend?
can somebody please help me?
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Here's a hint.
Imagine V1 is 2 V. The transistor's emitter is 0.7 V lower than the base voltage, so it is at 1.3 V. A current I = 1.3/Re flows. This same current flows through the collector (ignoring beta effects). So the collector voltage is 12 V - I*1k. Now, if V1 increases to 3 V, the emitter will increase to 2.3 V, and I will increase to I_new = 2.3/Re, and the collector will decrease to 12 - I_new*1k.
The gain is the change in collector voltage divided by the change in emitter voltage.