throbscottle
Well-Known Member
There's quite a neat trick you can use to protect power inputs of things from a reverse supply by connecting a p type mosfet with gate to 0v, drain to +V input and source to whatever you're protecting. It works by the intrinsic diode conducting the first bit of current, whilst the transistor turns fully on and presents a low impedance path "the wrong way" through it's body. Gives a lower voltage drop than a diode since you get the saturation voltage of the mosfet instead.
So I have been playing with my PSU design some more and realised it needs better protection against over-voltage at the outputs. A diode across b-e on the output transistor will protect it but can destroy the controlling transistor. A resistor in series to limit the current through the transistor plays hell with the current limiting circuit because the output can't drop to zero.
So it looks like I need a diode in series with the PSU's output, and was reminded of the reverse P-MOS trick. I'm pretty sure it will work, so I suppose the question is, what can go wrong?
So I have been playing with my PSU design some more and realised it needs better protection against over-voltage at the outputs. A diode across b-e on the output transistor will protect it but can destroy the controlling transistor. A resistor in series to limit the current through the transistor plays hell with the current limiting circuit because the output can't drop to zero.
So it looks like I need a diode in series with the PSU's output, and was reminded of the reverse P-MOS trick. I'm pretty sure it will work, so I suppose the question is, what can go wrong?