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I'm looking into getting a decent benchtop power supply ($150-300) for hobby-level electronic design and testing. I don't want to modify or use a computer ATX supply because I want:

  • Adjustable voltage
  • Adjustable current
  • Low noise/ripple
  • Accuracy
  • 1 or 2 voltage outputs
  • 0-30VDC (AC not needed)
  • 3-5A

As I look at various manufacturers' supplies, I am finding a few that seem like good choices, however I've encountered an aspect I am stumped on: Linear or switching?

I am planning primarily on small microcontroller projects, but I'd also like to do some audio and RF projects. I'm concerned a switching supply might have excess noise. Is this a valid concern, or are quality switching supplies more than adequate for clean battery-like power?

Also, should I assume that a supply which does not specify linear/switching on its datasheet is a switching type?

JYelton
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  • From this, I went on to ask about some specific power supplies in [another question](http://electronics.stackexchange.com/q/52033/2028). – JYelton Feb 13 '13 at 21:08

6 Answers6

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Get whatever meets your needs for voltage, current, readouts, size, price, etc. Don't worry about whether it is a switcher or linear.

In general, linears are less efficient. However, this matters little to a bench supply. The few watts or even 10s of watts it might occasionally draw more than the equivalent switcher is irrelevant. It will get hotter, but presumably since you are buying a whole box this has been designed in. Unless perhaps you have a very specific physical spot in mind for this box and there is little room for ventillation, the extra heat of a linear won't matter.

Switchers will have some switching noise on their output. Again, this shouldn't matter. Check the ripple spec, but the ripple of any finished-box commercial lab supply really shouldn't be that high, a few 10s of mV at most.

What exactly is the problem with ripple? Not much in a bench setting. Things like relays, motors, LEDs and even the occasional LEB (light emitting bulb) aren't going to care. But the most important point is that a well designed circuit should be fairly immune to power supply ripple. If your circuit can't handle a few 10s of mV of supply ripple, what's it going to do when it gets off the bench? In the few cases where supply ripple might matter, you should get into the habit of adding the appropriate filters anyway. For example, to power the opamp for the sensitive input circuit of a microphone preamp, put a ferrite chip inductor in series followed by maybe a 10 µF cap to ground feeding the opamp power pin. Other places may need a bit of filtering too, but that's something you should be doing anyway. Using the microphone amp as a example again, the final stage may draw enough power so that it makes its own "ripple" on your local supply, whether the original power supply was perfectly clean or not. This is just normal design practise.

So all this is a long way of saying don't worry about it. There are even hybrid types where a switcher does most of the work with a linear post-regulator that only drops half a volt or so to clean up the noise or let you get down to low currents and voltages nicely (which some switchers have a hard time with). Again though, you are buying the overall box. Look at what it does as a black box and don't worry how exactly all the specs were accomplished.

Olin Lathrop
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Linear power supplies are less efficient, and waste more power as heat, than switching power supplies. This also results in switching supplies being able to provide higher current for a given cooling arrangement of the power supply design, whether passive, fan-cooled, or something more exotic.

A well-designed switch mode bench power supply ought not have higher ripple or noise than a linear supply. When operated within the load specifications of the bench power supply, the output voltage quality should not be a concern.

Given that a linear power supply uses simpler electronic design principles than switching supplies, but on the other hand has heavier cooling needs, an assumption that an unspecified bench power supply is one type or the other is not justified, contacting the manufacturer would be your best option.

Anindo Ghosh
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    I disagree with your statement "A well-designed switch mode bench power supply ought not have higher ripple or noise than a linear supply." *No* switching supply will be as smooth or quiet as a linear, for the simple reason that the power train output of a switcher is never continuous - you're always reliant on output capacitors holding the output up during the period of time when energy is not being transferred to the load. Add to this all of the CM noise generated by the switching itself, and you have something that's quite noisy. – Adam Lawrence Dec 16 '12 at 13:26
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    This is why many switching power supplies for medical or other low-noise applications often use a lossy linear post-regulator stage after the switcher - to get rid of the HF ripple. – Adam Lawrence Dec 16 '12 at 13:28
  • @Madmanguruman I was *just* writing exactly what you wrote in your second comment: A switched mode bench supply will usually have a linear regulator at the output stage, to address switching noise. – Anindo Ghosh Dec 16 '12 at 13:30
  • Most commercial switching power supplies won't have the linear post-regulator. They're not good choices for lab work. – Adam Lawrence Dec 16 '12 at 13:31
  • @Madmanguruman I've opened two supplies up, both switched, both with linear output stages. YMMV. – Anindo Ghosh Dec 16 '12 at 13:33
  • Hopefully the switcher is kept at a constant output voltage and the linear part takes care of the volts and amps regulation, else there will be some corners where the performance will be bad. – Adam Lawrence Dec 16 '12 at 13:36
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Lab supplies that meet your specifications are very commonly used in industry and should be easy to find. HP/Agilent, BK Precision, GW Instek and many others make good bench supplies.

A purely linear supply will be large but will be the quietest solution. A switcher with good linear post-regulation (the linear stage will smooth out the switching noise and take care of the volts and amps regulation) will be almost as good and certainly adequate for the vast majority of bench work.

Most of the bench supplies I've played with are of these two types, and in practice they both produce DC that's cleaner than the typical flyback converter housekeeping supply used in many power supply designs. You should be fine.

A pure switcher, even with adjustable output, isn't the best choice for this sort of work. You won't get very clean output if you try to adjust the voltage very low (you may even get into cycle-skipping mode with larger-than-expected output ripple).

Adam Lawrence
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I'm concerned a switching supply might have excess noise. Is this a valid concern, or are quality switching supplies more than adequate for clean battery-like power?

You are correct, a linear power supplies should have less ripple and noise compared to a switching supply. Also switching supplies usually are slower at responding to fast changes in the load. Switching supplies, however, are more efficient, weigh a lot less, and produce less heat; all of these benefits you probably don't care about.

So when it comes down to it, for the price you mentioned, I don't think you can find a good switching supply (I may be mistaken,) but you can get a pretty descent linear one. I would think a switching supply in this price range would be fairly poor quality.

I am planning primarily on small microcontroller projects, but I'd also like to do some audio and RF projects.

If possible, stay away from high amperage (5amp and greater) power supplies, you most likely don't need anything near that much amperage, and they are usually cheaper units geared more for the uninformed buyer. Another thing I recommend, since you may be working on projects that require multiple voltages, is getting a dual voltage power supply. I have several, and they really come in handy. I just bought this one the other day, and it seems ok.

should I assume that a supply which does not specify linear/switching on its datasheet is a switching type?

I would assume linear.

Here is a video review of a cheap power supply, there are a lot of other good reviews on you tube too.

Also, a linear supply will probably be more reliable, and if it does break, you're more likely to be able to fix it on your own.

Garrett Fogerlie
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  • It's Dave! (Saw that review.) :) – JYelton Dec 17 '12 at 00:52
  • @JYelton when you get down to just a few units you like, you should create a new post and ask which one would be best suited you needs. – Garrett Fogerlie Dec 17 '12 at 02:13
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    I've considered doing that, but I wasn't sure product comparison/shopping questions would be acceptable here. – JYelton Dec 17 '12 at 02:32
  • @JYelton skim this http://meta.electronics.stackexchange.com/a/2507/9730 as long as you ask something to the effect of, "Which on of these power supplies would be best suited for doing bla" you should be fine. Since the question is not localized and should help others in the future. You could even link back to your question here to show the effort you put in. – Garrett Fogerlie Dec 17 '12 at 02:53
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The biggest problem I have encountered with switching supplies, or DC regulators that use a switching design, such as Boost Converters, is voltage drop under heavy load. My 3 Amp linear bench supply can deliver 2.5 Amps into a resistive load at 24V, and it only drops .2 V. My switching supply drops 2 V under same load, and a 12V-24V switching booster drops 4.8V under same test. Granted, the booster is a cheap chineese product, but linear seems to hold it's voltage better.

Brizee
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The nice solution is the hybrids: A switch mode AC-DC supply followed by a linear regulator to give the advantages of both worlds. (Of course the linear section decreases efficiency and increases cost a bit). They are seemingly (very strange in my opinion) fairly hard to find at decent prices today... Hameg and TTi both have expensive models using the concept. I have not found a finished design for the programmable 0~60V >3A I need. But this 0-24V 0-3A hybrid looks like a fair DIY starting point...

Gnyff
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