Looking for a relatively simple & low cost example of a Variable 30vdc 3A bench power supply

Thread Starter


Joined Jun 1, 2018
I'm wanting to make my own low cost bench power supply with Voltage and Amp displayed on 2 separate 4 full digit / 7 segment LCDs
I have scoured the internet but can't find any links that really fit my requirements (I am still fairly new to this so apologies).

Would like any links or suggestions to include a BOM, circuit schematic and also i wiring diagram (still haven't quite got my head around converting a schematic to a PCB)

My requirements are:
1. Capable of adjustable Voltage from 0-30VDC
2. Capable of adjustable current 0-3A
3. Able to be connected to this LCD Display https://www.jaycar.com.au/8-digit-7-segment-display-module/p/XC3714
If not able to be connected to this display, suggestions on what other displays I could use would be appreciated?

I don't want to by a voltmeter panel module & would prefer to reuse a display from an old alarm clock or DVD player or something similar.

Any links or advice would be greatly appreciated.


Joined Sep 7, 2010

eBay is always the best place ... the above kit is $10

but you will need a 24V AC input transformer (or perhaps 24V battery)...and heatsink and fan
digital LED voltmeters are $1

Another way to do this is harvest some li-ion cells from used laptop/cellphone batteries (my favorite pastime) they have a lot of use left in them and can deliver high currents ...make a 30V battery tapped every 3.6V. for variable supply
Last edited:
Build or buy?

I bought this one about a year ago for $60 and it has worked well for me every time. As per @crutschow , yes, that is a consideration and I did look at the specs...
- Output voltage: DC 0-30V Continuous adjustable
- Output DC Current: 0V - 5A
- Overall efficiency: ≥89%
- Display resolution: voltage: 0.1V , current 0.01A
- Voltage and Current adjustment
- Voltage regulation: CV 0.1% + 3mV, CC < 0.5% + 6 mA
- Protection: High current limiting and cooling fan
- Load stabilization: CV 0.5% +1mV / CC 0.5% +3mA
- Ripple and noises: ≤ 0.5%V P-P
- Cooling way: Intelligent temperature control fan.
- Dimension: 8.8x 3.2x 6.5 Inch
- Unit Weight: 3.2pounds

For me and what I use it for so far, it works.

If you are going to use that display, you are going to need additional circuitry to read voltage and current and then send that information to the MAX7219. Then there is the cooling fan, and the transformer (as already mentioned), and the case and fuse/breaker and so on. It's a nice project, but not really that simple, given your requirements. I didn't think I could do it for under $60.

-live wire-

Joined Dec 22, 2017
Here is what I recommend. Get a power supply like this. Then get a buck converter, with a display, that allows for constant voltage and constant current. You can go with one like this. If you want more power, you can go with one like this, and get a more powerful supply. The total cost should be between $20 and $50, while the commercial options are at least $60.