0-30V 3A Chinese Power Supply

Thread Starter


Joined Jul 17, 2020
Hi, this is my first thread.

I have the classic chinese DIY circuit Power Supply from ebay / banggood etc.

The problem I have is the same for two boards. If I connect 12v AC everything are working ok. If I connect 24v AC the LED indicator is always ON.

With 24v 3A transformer the Values are:

Illustration 2
A=31.5 V
B=-5.1 V My Zeners are 5,1V
C= 24V

Illustration 4
p1 for Current = 1,6V
p2 for Volts = 10.2V

U1 5.1V 2 and 3 leg
U1 A= 31 V

Zener beside the U1 is 10.35V

Thank you in advance
Last edited:

Audioguru again

Joined Oct 21, 2019
The TL081 opamps have no manufacturer's symbol and the lettering is upside down. Defective Chinesium opamps?
Videos of the kit show opamps correctly labelled from Texas Instruments.

The LED should turn on when the load current is higher than the current setting of the "A" pot. The LED is driven from a transistor that is driven from an opamp.