LM317 voltage regulator has internal short circuit protection alongside with its thermal overload auto-shutdown, but in the circuit below it will simply burnout when the output is shorted. And its adjust pin gets internally shorted with its output pin.
I know that a pass transistor would strip off the regulator's ability to stand a short circuit and limit current but whats wrong here ?
I built it more then once on different PCBs and they all end up the same way ( killed about 5 regulators till now as i though that something was wrong with my build)
one version of the PCBs i made :
Best Answer
When you short the output, Q1 heavily conducts and basically connects pin 1 (ADJ) directly to 0V. Between Vout and ADJ internally is a 6V zener diode and a 50 ohm resistor: -
It's very likely that the zener diode will fail short circuit (most of them do on over-current) rendering the device dead.
If it can be tolerated a 1k resistor in series with the ADJ pin will probably save it. The 50 uA ADJ pin current (normal operation) will cause a 50 mV error (times the standard R1/R2 feedback ratio) in the output voltage so there is a somewhat fluffy downside potentially.