I am designing a little class AB amplifier for a small circuit. This circuit is biased such that it has low crossover distortion. Below is a schematic:
As you can see, I have inserted 68 ohm resistors in series with the power supply lines. This is such that when the output is shorted, the current is limited to about +/-200mA. In this demo, I have inserted such a short; a 10m resistor. However, in operation the resistors dissipate 1.5W each and in short circuit conditions about 2.5W, which means I have to use two big and expensive 5W resistors to remain within safe operating boundaries, and it also might cause problems for the power supply.
So I'm looking for some way to limit output current to about +/-100mA before the amplifier begins clipping (which the current solution manages), but without the "hack" of using resistors on the power supply lines. I was considering a comparator measuring the output current across a shunt resistor, but I wasn't sure how to achieve this for short circuits of both polarities. Also, I need the circuit to ideally work up to around 5 MHz, which limits the choice of components.
Edit: Thanks to russ_hensel and opencircuits.com, I devised the following current limiter (including amplifier), which actually works really well (it clips the output and doesn't make it sag or invert, like some limiting circuits.)