Home made bench power supply

A bench supply always comes handy when you play with electronics on a daily basis. As anything else – if something comes handy you have to pay it`s price.
These supplies are quite expensive compared to the price of what is made of – basically you pay the engineering not the parts that are made of.

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Main parts

Because I was in the need of one bench supply I made my own, out of a few cheap components so I have spent 10 bucks(USD).

Parts list:

  • 2 x DC-DC converter 1.5v to 30v, 5 amps
  • 2 x 500k multi-turn precision potentiometer
  • 2 x mountable digital display amp and voltmeter
  • 1 x LM7812 voltage regulator with a heat sink
  • 2 x 40V 200uf electrolytic capacitor

Others:

  • a bunch of cables
  • a metal project box
  • soldering iron and flux
  • patients
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Wiring diagram of the Chinese step down regulators

First of all I had to supply the volt/amp meters with at least 4,5 volts to make it turn on but the dc-dc converters are able to supply minimum 1.5v – so when i have less than 4,5v coming out of the converters the meters are turned of so you have to measure externally the voltage, this was not an option so I made a separate supply out of an LM7812 and a pair of capacitors. The LM7812 is a 12V 1A linear voltage regulator which can support a maximum of 30 volts input, which is the maximum for the step down regulators too.

Inside look
Inside look

After finishing the feeding of the meters came the next step. I had to desolder those small potentiometers which were on the dc-dc converters and soldering in those fancy multi-turn potmeters, so they can be mounted outside of the enclosure. They worked by the first try so the supply was almost done.A few more moves and the supply was completed. And here comes the fun part, the testing.

It seems pretty much OK for using as a hobby tool, at the moment it perfectly fits my needs, but in the future a few improvements can be done. There is no protection for short circuit (only the buck converters IC internal protection which is enough for a few seconds), and also there is no feedback about the output so under higher loads the voltage drops significantly. Also adding extra output filter caps would be nice and would regulate that fluctuation which happens at around 4-4.5A load.