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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like the ZK-4KX (I don't want to post a link here because most of them are shopping links and they will be shortly out of date; this is easily viewable from a Google search).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.

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    \$\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

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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.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\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
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    \$\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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