ronsimpson

Here is a method of controlling the output voltage swing of an op-amp. If the output is too high the top transistor turns on. If the output is too low the bottom transistor turns on.
I am working on an audio amplifier with controlled clipping.
Set the “top clip” and “bottom clip” voltage to correct values.
If the clipped output has less than 5 volts swing do not use the diodes.
If the clipped output is more than 5 volts swing add the diodes.

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dazza000

where do I apply these voltages? to the bases of the transistors?
dazz000

ronsimpson

I just posted a third picture where the base voltages are set by a resistor divider.

In my case I set the base voltages to +5 and –5.
In your case you want the most positive swing to be 5 volts so set the top base at 4.3 volts.

speakerguy79

This is a ridiculously long topic for such a simple problem

dazza000

Well I gues your right, I've got plenty of info to go on now so its just a matter of evaluating these ideas. thanks to all who responded. Bye.
dazza000

Roff

If anyone ever needs a precision clamp, here's one. The clamping error voltage is only limited by op amp offset voltages, since the diodes are inside feedback loops. It will have a tiny bit of overshoot, dependent on the slew rate of the input signal and the bandwidth of the op amps (assuming they are not slew rate limited). Shown below is a sim using behavioral 10MHz GBW, single-pole op amps, operating on a 1kHz, 20V p-p signal and limiting it to zero and 2.5V. The clip limits can of course be changed.

Sorry, SpeakerGuy.

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	precision clamp sch.PNG (21.1 KB, 22 views)
	precision clamp waves.PNG (21.5 KB, 12 views)

__________________
Ron

dazza000

Thanks Roff for your considered answer.
dazza000