Hello all,
I am working on a circuit to detect the presence of an audio signal (from a pro sound card) and, from it, drive a resistive load. This isn't really an amp; I just need to sense a signal, then drive a power transistor into saturation as long as the audio is present.
I have a working prototype that uses an op amp, open-loop configuration, driving a power MOSFET. My load is on the drain side, grounded source. Audio is decoupled through a cap into the non- inverting input; the inverting side is biased to about 0.1 volt to keep the output low when no signal is present.
This all works fine, except that I only get output when the audio signal is in positive polarity, kind of like a class B amp, I guess.
Is there any (simple) way I can get my op amp to output high when the audio swings low?
Thanks!