Increasing the power rating of zener diodes

  
A power transistor can be used to provide a high powered zener voltage from a low wattage zener. A 400 mW zener can be used where a 10 watt zener is required or a 1 W zener can be used where a 50 to 80 watt zener is required by using appropriate transistors for Ql and Q2 in the circuits shown. Where low rating is required, Ql would be an ASZ 15 (germanium) or an AY9140 (silicon). Q2 could be a 2N2955 (silicon). For higher powers, Ql should be an ASZ18 (germanium) or a 2N2955 (silicon) and Q2 a 2N3055 (silicon) or an AY8149 (silicon).
Increasing the power rating of zener diodes  - schematic

A heatsink on the transistor is required. The circuit in A has the advantage that power transistors can be bolted directly on to a chassis which may serve as a heatsink.




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