comparator that latches

[treez]

I need a comparator that latches.

Its for short circuit protection……..if there’s a short I want the comparator to switch a series fet off to stop power flow into the short…then periodically the microcontroller will keep unlatching the comparator (allowing the series fet to switch back on) to see if the short is still there.

Do you know of any latching comparators?

All the ones on digikey are too expensive (ie $0.9+)

 

[FvM]

Similar features are usually achived by positive feedback, don't need a special comparator.

 

[crutschow]

As FvM noted, using positive feedback of sufficient value with a standard comparator will cause it to latch. You can reset the latch by momentarily breaking the positive feedback loop.

 

[Tahmid]

Which microcontroller are you using? If it has an internal comparator, you can use that and the 'latching and unlatching' can be done by software. You can also use the comparator output to feed the microcontroller which will drive the FET as required, instead of using the comparator to drive the FET.

Hope this helps.
Tahmid.

 

[FvM]

As an additional comment, latching overcurrent protections often involves the problem of getting triggered by inrush currents. An alternative is to use a linear current limiter and make the processor shut down the supply channel if the overload stays for longer than a few milliseconds, according to the circuit requirements and save operation area of the output transistor.

 

[picgak]

If you are using a microcontroller why you want a latching circuit, Once a short is detected micro can keep the FET shut for the delay you set and can periodicaly turn on and test for shorts

 

[treez]

thanks, i dont want the micro too involved in s/c management...id rather do it in analog circuitry, and keep the micro free to do the emergency lighting functions.

I'll look into what you say.......this is for a boost converter runnign off a battery (3V6) and i am wondering about changibg to a flyback, since the comparator is going to have to be hellishly quick to trip without drawing a huge current spike through the poor NiCd batteries

 

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