Generally there are situations wherein a higher power Zener diode is essential and one is not easily accessible.
Listed here is a circuit which using a power transistor can easily increase the power rating of any Zener diode.
By just shunting the transistor's base collector junction with a low power Zener and when the gain of the transistor in the functioning current surpasses 30, then along the collector emitter leads the BJT may work as a Zener diode.
If the existing diode is a 250 mW device then the power dissipation of the system will likely be 30 x 250 mW = 7.5 watts.
It has to be taken into account that this Zener voltage therefore acquired will probably be 0.7 V greater than the diode rating.
Hence if originally a 6.8 V diode was employed then the new voltage will likely be 6.8 V + 0.7 V = 7.5 V. Hence for a power of 7.5 W, the highest allowable current of the zener shall be 7.5 W/7.5 V = 1A.
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