This power supply circuit uses a LM317 or 7805 regulator chip to do the work. The problem is that when the wiper arm of R1 is turned to the position closest to the top, it will short the output to the common or adjust pin. This will cause the R1 pot to overheat and burn out and possibly damage the regulator and/or other parts in the circuit. This is not a good thing to do. The solution is to put a resistor between the top end of R1 and the output pin so that the total resistance cannot be less than a certain amount. R1 is 10k so a resistor of 470 ohms seems to be a good choice to start at. It will reduce the voltage adjustment slightly, but that’s better than burning up, now, isn’t it?
2012-05-12 Power Supply Self Destructs
