foldback triggered timed trip/shutdown?

Discussion in 'General Electronics Chat' started by jimmiegin, May 13, 2014.

  1. jimmiegin

    Thread Starter Member

    Apr 4, 2014
    Hello. I am currently researching psu design and am now onto short circuit protection. I have been looking at the foldback and am wondering what I would have to search for on google to get info/tutorials on trip switches set off by a foldback. I figure that instead of connecting emitter to Vout it would be much better to have some sort of set up where the emitter connects to a shut off circuit, maybe a trip or a shut off with a timer with led and buzzer to tell you when its not happy on overload. What is such a circuit called please? it may be a dumb question. I am looking for tutorials so I may learn principles of shut down devices and trip switches so a point in the right direction would be really helpful please. Thank you
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    Most psu use current monitoring or over/under voltage monitoring using op amps and transistors, plenty here to have a look at

    Atx psus
  3. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    "connecting emitter to Vout" sounds like a linear voltage regulator. If so, what are the output voltage, current, and adjustment ranges, and overcurrent trip value? Also, why are you going with foldback as opposed to constant current limiting? I'm not saying one is better than the other, just need some background to shape a response.

  4. #12


    Nov 30, 2010
    I've done it both ways. I highly admire the foldback method but I had to do this in AC at one point. I guess I'm saying that I wouldn't bother to design something to assist the foldback method because it works like a charm.

    If you do, it's a current detecting resistor to a bipolar transistor (or an op-amp or a comparator) that fires a load of current into a capacitor on a mosfet gate and the mosfet disables the driver of the power supply. You can put an adjust pot on the sensor and you can put a latch-out instead of a delay on the mosfet side.