I am trying to design a circuit that will switch off an output if it is shorted. The normal output is an squarewave of around ± 14V to ± 18V @ ≈ 8kHz. Sound simple but I don't like simple. I want it to be a little smart. I want to detect the short and and if it is longer than say 100ms remove the O/P but (always a but) I want it to reapply the O/P after about 2 secs. If the short is still there the cycle continues.

Although I said I don't like simple I also don't want an overly complex cct. I was thinking of using a MOSFET for switching and simple R/C timers. My biggest problem is detecting the short/over current.

TIA

 

Consider using a load resistor as in a metering circuit. Then measure the voltage drop over the resistor and feed it to an op amp instead of a meter. The opamp can then do what you want.

 

Thanks for the reply. I am sure that I will end up with an op amp in there somewhere but I am not sure just a resistor will do the job I am looking for. Being an AC voltage I can see the op amps out put will be AC and would in turn be switching the O/P on and off at the AC rate. I maybe trying to think about this the wrong way.

Another thought that had crossed my mind was a precision rectifier but I am not too sure how they would work with an 8kHZ squarewave.

Also forgot to mention this 8Khz Squarwave is also PWM. Not sure if that will have an effect.

PS. 10 browny point to the first who can guess what this project is for.

 

Bumping here.

I found a current sensor, IN196, and it says it has a 500Khz BW. Does this mean it will detect an AC signal across its sense resistor? If so what would the O/P be? Would I need an intergrater on the output?

Sorry for all the questions but my brain is just not working really well at the moment.