re voltage regulation and current limiting acollins uclink berkeley edu andy collins writes one not so quick question to throw out there for you guys for our class project we need to design and build a power supply to the following specs voltatge adjustable from v current limited at a voltage must stay within of designated value for i from a ac ripple less than mv rms of course we can t just use an adjustable voltage current limiting regulator chip our problem is with the current limiting i e we ve found stuff to do the rest of the parts of the circuit what the supply must do if presented with a load which would draw more than a given the supply voltage is reduce the voltage so that the current will equal one amp thus if we were to short the thing with the ammeter we should read one amp if we measure the current through a ohm resistor at v we should read one amp and the output voltage by necessity must be v the only basic idea we have seen for the current limiter involves a circuit which will pull current off of the base of the output power transistor and therefore reduce the output so does anybody have any ideas we could work from thanks in advance andy collins kc yey acollins uclink berkeley edu ps if anybody wants to flame this as a stupid project i agree fully but i still have to do it its graded you can design for ramp shutoff brick wall current limit or even fold back cutoff sounds like you want brick wall current limit your lead is correct to pull down the bias to the series regulator base drive in order to get the brick wall you need enough voltage gain on the current sensor normally a darlington on the current sensing resistor will be adequate but for infinite gain use an op amp to sense the current releative to a stable voltage reference and use a driver to turn off the base bias on the series pass transistor phase compensation may be necessary with this closed loop control system if yopu have more than degrees phase shift in your feedabck circuit at unity gain ok dino inqmind bison mb ca the inquiring mind bbs winnipeg manitoba
