FEEDBACK SERIES STABILISER

The operation of the simple emitter-follower circuit can be improved by including amplified feedback control as shown in the base circuit of Fig. 21.6. A zener diode D is used as a constant voltage reference, being biased into the breakdown region through the reistance R1. The diode holds the emitter of tansistor Q1 at the constant reference voltage. Any variation on the output voltage appears at the base of Q1, is amplified, and fed to the base of the series control transistor Q2, resulting in the collector-to-emitter voltage of Q2 changing to oppose the initial output variation.

 

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Fig. 21.6 Basic series-stabiliser ...

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