Adventures in Science: How to Use a Bench Power Supply

Looking to upgrade your workshop or mad science lab with more power? Here's how to get started with benchtop power supplies.

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After covering the basics behind using digital multimeters, I knew that I had to talk about how to supply power to a project. This week in Adventures in Science, I go over the basics of how to use a bench power supply.

Bench power supplies are extremely useful tools in testing circuits, as they allow you to adjust the voltage on the fly. If you have a project that needs a specific voltage or if you haven't quite designed the power section yet, the bench power supply can be a life saver. You can also watch the output voltage of regulators with an undervoltage lockout feature as you slowly decrease the supplied voltage to make sure it cuts off power when necessary.

Some units can be configured to act as a constant current source, and most will allow you to set a current limit. You can use this feature to characterize and test diodes (i.e., how much current flows through a diode at a particular forward voltage).

If you want to read more about powering your project, we have this fun tutorial, even if it doesn't focus solely on bench power supplies:

How to Power a Project

February 7, 2013

A tutorial to help figure out the power requirements of your project.

I know that I skimmed over the uses of the power supply in this video. Can you think of any other reasons to use a bench power supply over a simple wall adapter? Post your ideas in the comments below.


Comments 15 comments

  • Other reasons to use a bench supply over a wall wart? Bench supplies just look way cooler. The more indicators and digital meters you have, the more your friends and neighbors will think you're a mad scientist. When they're scared to enter your workshop, you've arrived.

    I guess also the fact that you can turn off the supply without having to unplug it.

    • sense leads to compensate for voltage drop in test probes
    • power supplies are the gateway drug to tools like a dc power analyzer (n6705b)
    • Scpi commands are great for automation and/or debugging
    • Power supplies have inhibit lines which are good for trigger inputs off an oscope
    • some power supplies have a dmm
    • Nice! I particularly like referring to power supplies as the "gateway drug." Sorry about your wallet! :)

  • I'm not at all enamored of the "art work" -- it is FAR to easy to cause eye damage looking at an electric arc (not to mention that it's also easy to start a fire).

    Anyway, that having been said, I've got three "bench" power supplies I got from Radio Shack back in the 70s. (Two of them were "pre-built", the third, a dual supply, came as a printed circuit board with directions and a parts list that you could get everything at RS [or at least the RS stores in western states, which were unlike the ones I encountered in my time in the mid-west that were usually "out" of about 2/3 of the parts they were supposed to carry].) All three have needle-type analog meters! (One "lives" on the bench, the others are packed way.) Although there are some advantages to a fancy one like you show in the video (and I have used similar ones [and even had to repair a couple of them -- I was sitting at the bench, with one turned on but not yet connected to a load when it started emitting smoke -- turned out one of the electrolytic caps was bad, and my boss said to go ahead and "shotgun" replace all of the electrolytics in both supplies to avoid a repeat]), IMHO for the vast majority of folks, the only thing you really need is one with an adjustable voltage. These days, my bench supplies get little use -- I use "wall warts" instead, as most of my projects need either 5VDC or 9VDC. Today's switching wall warts take so little power (well under 1W) that I usually just leave a couple plugged in. (Fortunately, the problem from the early days [around 1980] of switching power supplies not wanting to have less than about 10% load was solved back in the mid 80s.) One thing I do recommend: LABEL THE PLUGS on the DC end with the voltage and current ratings! (Some projects don't like getting the wrong voltage!)

    Given that many projects are using today's "standard" modules as components (e.g., Arduinos, Raspberry Pis, etc.), many of which include a voltage regulator, I frankly think that most "hobbyists" would do better to put off getting a "bench" supply until they really need it, and stick with wall warts (or maybe batteries) and things like the breadboard-friendly jack or Adafruit's jack-to-screw-terminal or jack-to-alligator clips adapters.

    Shawn, an idea just occurred to me: Go to the next ham-fest in your area and see if you can get an old (analog) oscilloscope for a few bucks (very likely <$40, maybe as low as $5), then show what you can do with one of these. IMHO, an o'scope is a very good learning tool, and those old clunkers can be a much more economical starting point for the "beginner" than the DSOs that abound in today's market.

    • Don't worry, I was wearing full welding gear for the "artwork." Well, except for the goggles. Probably should have upgraded those. Oh well.

      I agree that wall warts are quite handy. I almost always have a spare 5V USB micro hanging around somewhere on my desk. However, when trying to design something for battery operation, and I need to test the complete range of voltages for the battery(-ies), nothing beats an adjustable voltage supply. For the beginner, a fully-featured power supply might be a bit pricey.

      As for the old scope, I'm already on it. Shame it's not mine, though :)

      • OK, I'll grant testing to verify that something designed to run off 5V will run off the (nominal) 4.5V from 3 AA[A] cells, dropping down to the 3.x from a lithium, or even down to the [nominal] 3V from 2 AA[A] cells, and even getting an idea of "how dead" the batteries can be.

        BTW, I'm more worried that someone will "get ideas" from the "artwork" and try it without the proper gear.

  • A bench supply has many advantages over wall warts. That bench supply will give you 5 volts when the meter says 5 volts. I've seen unloaded 5 volt wall warts output as much as 9 volts! My bench supplies will shutdown when too much current is pulled, a wall wart will go up in smoke, or your project will!

    • So true about the additional protections in the bench supply! Wall warts will usually drop to their rated voltage when loaded, but it may not be as accurate as the bench supply.

  • Programmable power supplies can be used to simulate the behavior of batteries. You can model the rate of voltage falloff due to the actual current load, for instance. This can be very helpful in figuring out how long your circuit is going to last with a given set of batteries without actually wasting the batteries themselves on a test. You can also use it to see how your circuit responds to different types of batteries, to make sure it always performs adequately, regardless of what your end-user throws at it.

    If you add in a Programmable Load, you can model things like the failure points of Lithium Ion batteries, and check whether a charging circuit is performed correctly, or if it instead causes batteries to fireball without actually causing a fire hazard.

    • That's a good point. I forgot to mention programmable supplies! Can you recommend some that are fairly inexpensive for beginners?

      • I wish I could, so I could then buy it from you guys. But, given their uses, hackerspaces really aught to spring for them over the non-programmable kind; after all, who isn’t using batteries these days, and who doesn’t need to consider the voltage drop of battery drain on their circuit?

  • Off the top of my head, here are a few advantages to bench supplies over wall warts. They're better protected, so if you overload them, inadvertently connect them to some other voltage, etc., they'll usually survive intact: wall warts can be destroyed or blow internal fuses that are annoying to replace. They're well regulated, whereas wall warts can provide anything from DC to DC that varies with the load (I've seen double and triple the rated voltage at light load), half-wave rectified DC (basically pure ripple), or even AC. The grounding on bench power supplies is generally well-defined and explicit: the best ones are floating, so you can tie either the positive or negative output to ground, and "stack" supplies to add voltages or provide intermediate voltages. Similarly, many offer "tracking", so you can adjust multiple outputs in synchrony (useful if you happen to need equal positive and negative voltages). Here's a picture of a project that's getting a lot of use out of a triple-output power supply for circuitry that runs on several different voltages (the little boards hanging from wires in mid-air are additional regulators for yet more voltages).

    • All good points! That's a nice supply. After dealing with knobs, I would love to have a real number pad on my PSU :)

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