DIY Adjustable DC Switching Power Supply

If you are interested in DIY adjustable DC switching power supplies, you may want to take a look at this article.

If you happen to have a 24V 360W aluminum-shell power supply, you might suddenly get the idea to modify it into a 40V, maximum 15A constant voltage and constant current adjustable power supply.

First, you need to create a basic schematic diagram of the adjustable power supply:

After modification, the top side view of the internal board shows changes, while the bottom side is entirely routing traces. You keep the original temperature-controlled fan module, remove the overvoltage protection voltage regulator diode, and replace the output filter capacitor.

You can modify the standby power supply by using an open-loop 16V LED isolated constant current power supply.

You adjust the voltage on pins 2 and 15 of the TL494 to make it adjustable. You use shielded wires to bring them out to the front panel.

If the positive output terminal hole is occupied by a voltmeter, you can directly solder it onto the copper trace on the board. If you want to adapt a 50A ammeter on the negative side, you can use manganin wire as the lead. The hollow area at the lower left corner of the board is used to fix the voltmeter.

You solder the positive terminal here. Since high-temperature soldering is required, there may be discoloration and residue.

You install and test the 50A ammeter on the negative side.

The IEC “figure-8” power input socket: if there is looseness in the top shell opening, you can add a layer of insulating foam. The side uses copper wire with insulation for bundling and grounding purposes.

Below is the voltage adjustment potentiometer, and above is the current adjustment potentiometer. The shielded wires are connected here.

The front panel is arranged like this, combined with the original power supply casing. This layout still looks quite good.

The output voltage cannot be adjusted down to zero; the minimum is 0.06V because the TL494 comparator may also have an offset region.

Under load testing, the electronic load has also just been newly soldered. With a 300W heat sink under load, you can touch it without it being too hot, but the temperature-controlled cooling fan is running close to full speed.

The maximum current limiting is 15A. The original design is also 15A, and you only added current limiting adjustment.

The maximum output voltage is 42V. The original power supply is 24V, and since the transformer turns ratio was not changed, it cannot sustain a heavy load at 42V. You should remember that it will start voltage drooping after 3A.

Finished.