COMMON-COLLECTOR AMPLIFIER

The common-collector amplifier shown below contains an emitter resistor but the collector is connected directly to the positive rail. The base is biased by 2 resistors. Supposing that

·       the quiescent emitter current is about 1 mA,

·       the voltage present across the emitter-resistor R3 is 7.5 Volt,

·        bringing the output to exactly half-way between the supply rails.

·       To provide for a vBE of 0.7 V, it needs to hold base at 8.2 V.

·       The values of R1 and R2are calculated to provide this.