DC power supply cannot be regulated

A DC power supply, a high-speed DC motor with an emerald engraving machine can adjust the speed through a potentiometer.
The current fault: It can not adjust the speed, the multimeter detects, the DC output is 42 volts, and the output voltage of the potentiometer remains unchanged.
So I suspected that the LM723 was broken, then I changed one, and the fault remained.
I studied the datasheet of LM723, it seems that is not broken. I was still confused.
Ask for ideas, thanks in advance!

There are several possibilities here. The best place to start is probably the pot. There should be positive voltage (probably from the vref pin on the 723) on one end and ground (or at least a lower voltage) on the other end. The voltage on the wiper (likely connected to the negative sense input on the 723) should vary when the pot is turned. If the wiper voltage on the pot is not changing when the pot is turned, then look for a broken wire to the pot (such that the lower voltage end of the pot is disconnected) and/or replace the pot. Another possibility is that the pass transistor has shorted meaning that even though the output voltage from the 723 is changing the motor voltage does not (indicating the pass transistor has shorted.) In that case replacing the pass transistor should fix things. Hope this helps!


Oh, yep! I got it! Thank U very much!

bro i need Step-up converter from 0.9V ~ 5V to 5V USB. plese help me bro

There is one with a Fritizng part here:

If this doesn’t suit a google search for 0.9v to 5V step up converter should turn up a bunch of alternatives (but then you would need to find or make a Fritzing part for it!)


okee thanks for your information bro