Just for fun I want to make a lightweight, cheap, adjustable positive/negative bench power supply. "Lightweight" means that using an old PC ATX power supply isn't suitable as a basis. Requirements are as follows:

  • adjustable voltage
  • regulation from near or below 3.3v to at least 24 to (better) 30v
  • at least capable of 1A output per rail
  • constant current limiting (adjustable)

My idea is to find a couple of cheap modules like the ZK-4KX (I don't want to post a link here because most of them are shopping links and they will be shortly out of date; this is easily viewable from a Google search). Then I can use eg some Lenovo power supply bricks and wire the circuits so that:

  • The first power supply brick/ZK-4KX module combination will make the negative supply, and its positive will become "ground".
  • The second power supply brick/ZK-4KX module combination will make the positive supply, with its ground connected to the positive of the above, and its positive will of course be positive supply.

Like this:

Block diagram

Using a two-wire laptop power supply, the two modules will be isolated and I should get a regulated +- bench power supply. I will make sure to not use grounded power bricks.

Used laptop power supplies are a dime a dozen and of course the ZK-4KX modules are under $10 each on Amazon, eBay, Aliexpress.

Does this sound like a reasonable approach? Intuitively, it seems like the CC of the "negative" supply would not act properly but I can't say why. I'm not an electrical engineer, just a hobbyist.

Thanks for any advice. Essentially I want to do what this guy is after: Adding an adjustable constant current option to a LM5175 circuit but I like the ZK-4KX because most of the work of the Constant Current section has been done.

Furthermore: I do have one of these: https://www.bkprecision.com/products/power-supplies/1761 but I want something more portable, so I can play with Arduino circuits on the kitchen table, while my daughter does homework. I understand that the cheap Chinese circuits usually don't work to their spec etc., but I am also willing to take the good with the bad. At least at this point.

  • 1
    \$\begingroup\$ Buying from the sources you mention doesn't sound a reasonable approach if you want the opinion of a pro EE. \$\endgroup\$
    – Andy aka
    Commented Nov 27, 2023 at 17:30
  • \$\begingroup\$ @Andyaka I understand the risk. However, it's certainly not a requirement of this project. If there's something similar that's available from a reputable dealer I would love to take a look at it. \$\endgroup\$
    – Mike S
    Commented Nov 27, 2023 at 18:26
  • \$\begingroup\$ @MikeS another suggestion would be to use a single power brick and use a single to dual rail buck/boost converter (<$10 Canadian from china). They are essentially two buck/boost converters on one nice board (one pot for V adjustment). For your application, they would work perfectly! I use one for my low-power op amp prototyping with no issue. I have a barrel jack connected to the Input, and a 3-terminal block on the output. \$\endgroup\$
    – Pxl
    Commented Nov 27, 2023 at 19:12

1 Answer 1


To provide a formal answer, here is my take.

For hobby use where noise and minor inconsistencies don't matter, your design will do exactly what you need it to do.

I would suggest connecting a dual-pot to tune the + and - voltage in sync with each other, and have a +5V regulated output as well (for the Arduino and TTL level logic.

An alternative to your two power brick + buck/boost converter design would be to use a Single-to-dual-rail Buck/Boost converter. This will reduce the power bricks needed to one and provide a single pot (in some boards) to tune the voltage of both rails.

I would post a link to a product or two, but those links change too often for it to be of help. Search `dual rail buck boost converter' on Amazon or Aliexpress.

For low noise use I would suggest you buy a calibrated unit (expensive), or build a Linear power supply with a 2 to 3 terminal transformer from mains, then regulate the terminals as a dual supply. You can search common hobby kits for schematics by googling Dual rail linear supply circuit. You can even get fancy by having a feedback signal to an op-amp or Arduino to control the voltage.

Small instances that require a set negative rail voltage, for example, a single ADC or Op Amp, you can use a charge pump IC or discrete circuit. These will work great, but power/current output will be low.

The quick fix: Two 9V batteries connected in series with the center terminals being your ground. Great for the quick prototype, and even portable units that require dual rail supplies.


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ I have searched for the power supplies you've mentioned- just now, and quite often in the past. I have yet to find one that includes: Constant Current mode and the voltmeter/ammeter already built in. Given that I just saw a pile of Lenovo power bricks at a thrift shop for $3 US, I think that's the quickest and thriftiest way to go- even if a little weird. It gives me everything I want, and UL listed quality 19V power. I like UL listing on anything I plug into mains. I'll go cheap on the low voltage stuff. :-) But I do have a B&K 1761. It's just bulky for dinking around with Arduino. \$\endgroup\$
    – Mike S
    Commented Nov 28, 2023 at 13:49
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    \$\begingroup\$ I like your idea of adding additional +5V power. I'll add that to my design on the +V side. \$\endgroup\$
    – Mike S
    Commented Nov 28, 2023 at 13:50
  • 1
    \$\begingroup\$ @MikeS Thrifting for electronics used to be how I acquired electronics parts as a kid (and then I found online shopping)! For your application, having two power bricks will work as intended. As for constant current, you can use some power transistors to create a current mirror and use that as a current limiter. For applications where CC is needed, usually it would be a current source, which a howland current source or current mirror can do. CV is primarily utilized and the CC function on a PSU would be (in my case) used as a protection or limit for when I inevitably short something. \$\endgroup\$
    – Pxl
    Commented Nov 28, 2023 at 17:02
  • \$\begingroup\$ @MikeS I just had an additional thought: You may be able to find a buck/boost with current limiting functionality as well. I believe they exist somewhere out there. \$\endgroup\$
    – Pxl
    Commented Nov 28, 2023 at 17:04

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