Is this possible?

Thread Starter


Joined Jul 29, 2007

Here they hv suggested to use mosfet in place of relay. Now there r three pictures of circuits.
I want to use mosfet configration from circuit 1 with mosfet driver circuit from circuit 3. but i want to use single power supply.
Most interesting part i want is : i want to use this as speaker protector. Hence first the mosfet will conduct full.
then as the driving circuit voltage increases the current through the mosfet switch must reduce. So during overload
mosfet will work like bulb protector i.e. it will conduct less.
Is this possible?
If yes, then guide me how to do this?


Joined Apr 20, 2004
What you are describing is an AGC circuit. Protecting speakers from faults requires the interruption of the current path, not a gentle increase in series resistance.

Using the FET's is simply trying to open the path to the speaker before the current surge in the voice coil has thrown it across the room. It may be better than a protection relay to keep the speaker from being damaged, but this is significant mainly for large amps - something over 50 watts.

If the concern is about overdriving the speaker with too much signal, it's better to use a voltage controlled amp in the signal path, and reduce its gain when the driving signal exceeds a set limit.