Build Your Own Import Variable Lab Bench Power Supply

Does it ever just kill you that someone in a factory somewhere got to have all the fun of assembling your bench tools? There are a lot of questionable circuit boards floating around the Internet, and they can replicate practically any section of a circuit. When it comes to putting a prototype these days you can pretty much just buy each block of your system’s overview flowchart and string them together. [GreattScott!] combines a few of these into a relatively useful variable power supply with current limiting.

Admittedly, this is more of academic exercise if your only metric for success is monetary savings. Comparable power supplies can be purchased for the same amount of local currency as the parts in this build. However, there is something to be said for making it yourself.

The core of this build is based around the¬†LTC3780, a bit of silicon from LT that offers both buck and boost converting along with a current control mode. It’s useful for a lot of things. The here is rated for up to 130 watts of power, which makes is a decent amount of power for a bench supply.

With a few modifications, like replacing the world’s most untrustworthy potentiometers and adding a nice ABS box, the build is completed. Along the way, [GreatScott!] offers a few tricks for testing and some reminders of how not to make yourself dead when playing with electricity.

The end is a working lab bench supply project that can easily keep a hacker entertained on a lazy Sunday afternoon.

14 thoughts on “Build Your Own Import Variable Lab Bench Power Supply

  1. Heh, when I saw the glass of water, first thought he was using it as a variable resistor..

    But anyway, yah, that’s why I save headlamps and stop and tail lamps with only one filament burned, handy loads, instead of making ceramic wirewound power resistors glow.

    1. I did this with smaller, terrible converters sourced in a Bangkok scrap shop and added an R/C battery input plug to make it portable.

      It’s so noisy I use it to test piezo buzzers. With filtering or a linear voltage regulator, it can power microcontrollers (otherwise they tend to get stuck in a reset loop). It’s barely useful as test equipment. So that’s your worst case scenario for a functioning device I think.

      It does let me power or charge some low-power DC devices during extended blackouts, or rig things to scrap solar cells strung together. I salvage a lot of lithium cells, and a 22 watt*hour pack can keep the emergency lighting going for a good 6 hours with it (where I live this is a practical thing to have). So as a benchtop supply it was mostly a failure but it came in handy in other ways.

  2. A bench supply that is a buck-boost switcher?

    LT does make great parts in terms of features and efficiency in power regulators, but a bench supply’s purpose is to supply clean power and not add new variables.

    A linear bench supply is the second best thing to a battery.

    Buck-Boost supplies tend to have nuances right at the transition between operating modes.

    Current mode control with a boost regulator must be interesting, I guess the part would have built-in slope compensation.

    http://cds.linear.com/docs/en/design-note/dn369f.pdf

    http://cds.linear.com/docs/en/datasheet/3780ff.pdf

    It looks like the skip-cycle and boost modes have the most switching noise. You’d be better off starting with a higher Vin than you need and keeping the part in a buck-mode.

    I’m amazed at how quiet the discontinuous mode is.

    1. Kind of depends what you are doing though. I have a bench supply because I got it cheap. Most of the time though, I’m just testing LEDs, widgets, or powering some small micro-controller setup. It would be kind of nice to have a switcher based supply that doesn’t take 10x the power to test something for a few days, or weigh 10 pounds when I want to move it around. I live in a condo so my ‘workbench’ moves around between my desk, small fold up tables, and my dining room table; then has to get stored somewhere.

    1. I -think- any posts that contain links are going into some sort of moderation queue? I posted a comment with a link a while ago and didn’t see it right away, then a while later it magically appeared. Some sort of manual approval is the only thing I can think of.

      1. Yes. More to the point though, why are the article authors seemingly not allowed to post anything other than a youtube link these days?

        Seriously. I can’t skive off at work with a youtube, I want me some text and the odd picture.

  3. The rightmost potentiometer controls the undervoltage protection… we do not care about that so DON’T TOUCH it
    — said right after he turns it all the way to the counter-clockwise —

    LOL

  4. Is the water good for those resistors? Can the ceramic absorb it causing a problem? Is a hot-enough-to-melt-solder device dropping into water a bit too much thermal shock?

    I have an old aluminum cooking pan (which of course is no longer used for cooking) that I use for this sort of thing. Of course you do need to make sure the conductors don’t contact it and short out….

  5. I like to pull those AC sockets off of old computer supplies. Often times they have a little PCB attached with a noise filter. In this case I’m not sure if the noise filter would be doing more good protecting the device from noise coming in on the AC line or protecting the AC line (and all the other devices connected to it) from noise generated by the cheap internet bought switching circuitry in the bench supply. Either way… not a bad thing to have!

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