Electronic – Benchtop power supplies: linear vs switching?

power supply

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?

Best Answer

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.