External signal to trigger a PFET once only???

[ridgerunnersjw]

I have a PFET in series with the high side of a Battery. I have an external signal that will come in and go anywhere from 0 - 60V. I want that signal at ~2V to turn on the MOSFET. I will use an NPN transistor most likely here. Now for the ugly piece. Once the PFET connects the battery to the circuit I don't want any other edge of the external signal to turn off the NPN. That is to say the external trigger signal 'could' drop below 2V due to a loading surge thus toggling the NPN to shut off. Basically I want to latch the rising edge of the external signal at 2V and bootstrap my battery on and never have to worry about any more edges from the external signal.

Any ideas on how to do this???

Thanks

 

[IRstuff]

Huh?? You answered your own question:

Basically I want to latch the rising edge

Remember set-reset flip-flops? cross-coupled NOR gates?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[electricuwe]

The most simple way to design a latching circuit would be the use of a thyristor. Either you find some small signal thyristor or use the equivalent circuit consisting of a NPN and a PNP bipolar transistor.

See:

https://media.digikey.com/pdf/Data Sheets/NXP PDFs/BT169_Series.pdf

https://en.wikipedia.org/wiki/Thyristor

Such a thyristor would stay latched as long as the current stays above the holding current.

 

[biff44]

An SCR will also act as the thyristor mentioned above.
on the SCR gate, it you put a voltage there above the trigger level, DC current will flow thru the SCR, and will continue to do so even if the gate voltage goes back to zero.

your big problem is that this trigger voltage is between zero and 60 volts, which would probably blow out the gate in the SCR. So you probably need some sort of series resistor/shunt zener diode to translate the 0-60V range to maybe 0-4V. THEN apply it to the scr gate.

flip flops will do this also, but once again, the 60 V will blow the digital gate up.
you could make your OWN discrete transistor flip flop that could work on 60 V signals.

you could set up a relay to latch once it is energized. You would need a push button switch to de-latch it.

You could use various solid state relays, who use an optoelectric device to take the input control voltage, and then output a switched high current signal. there probably are latching solid state relays....