A simple pulse generator. ( R , C , op )

This is a pretty basic generator. The pulse width is set by R,c, Vcmp and Vin. The width of the pulse is set by the differentiator at the front end (although it's not really that practical as shown due to slowly rising / falling edges which most comparators have problems with). The rising edge at the + input will follow Vin very closely, which starts the pulse. The end of the pulse is determined by the decay of the differentiator (proportional to e ^^t/RC). When it falls below Vcmp, the output will go low again.

Don't tell me you've never seen a simple differentiator before :)

Cheers

PeteS

(proportional to e ^^-t/RC)

Cheers

PeteS

What goes up must come down. Some opamps/comparators will go bonkers when the trailing edge slams the input below ground.

John

That's why I mentioned it wasn't very practical as drawn, although I didn't go into _all_ the reasons it was impractical :)

I've seen nasty phase reversal _without_ the input going below ground - just going below a certain level with loop gain high enough. I'm not a chip designer, but the reasons are fairly well known by now :)

Cheers

PeteS

PeteS =E5=AF=AB=E9=81=93=EF=BC=9A

One more question, does this circuit possible to happen bounce effect? ( at comparator output side )

The VDD(VCC) for the comparator is keep on ( about 3.7 V) always, Vcmp is about 0.x (V), divide by two resistor, ( gnd is 0V )

Best regards, Boki.

You've gone and reinvented the Poor Man's One-Shot. I learned about this in USAF tech school, but they used a transistor back in 1968. ;-)

Cheers! Rich