Friday, January 8, 2010

Why we use PNP power transistor in Isolation circuit?

The signal from optocoupler is first given to PNP power transistor


before giving it to Relay. Why is it so?Why we use PNP power transistor in Isolation circuit?
The PNP transistor increases the current to enough to drive the relay. The signal to the transistor would not be able to drive relay without the PNP to boost it.

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