Electronic – Considerations in a bench/lab power supply

equipmentpower supply

I'm looking at adding a low-cost variable power supply to my electronics hobby bench. After years of cobbling together LM317's and LM7805's, it's about time…

Considerations:

I've found a few options which I am unsure about.

Dave at EEVBlog states in various videos (#8, #30, #166 (@04:16), #168, #272, #314) that you should look for the following:

  • Multi-turn knobs for voltage and current adjustment (as opposed to pushbuttons and separate coarse/fine knobs)
  • A power supply that can range from 0 volts on the low end instead of 1 or 1.2 volts
  • A switch to turn on/off the load
  • The supply shouldn't overshoot the target voltage when switched on
  • It should have a separate mains earth ground terminal (to allow combining supplies)
  • Prefer linear for less ripple and noise (though switching offers smaller size and cost for higher currents)

Of course some factors depend on the intended use, some depend on preference, and some depend on budget.

(My intended usage is primarily microcontroller projects (3.3V-5V, <1A), automation and control projects (solenoid, stepper motor, etc) (12-24V, <5A), and low voltage lighting projects (12-24V, <3A). Budget ideally < $300.)

I asked earlier about the last point, linear vs switching, in a previous question. Olin convinced me that the disadvantages of a switching supply are minor, and certainly for my application, make sense for budget, bench space, and other reasons.

Thoughts:

To touch on the other points:

  • Multi-turn pots must be preference. I think they are better than single-turn pots, but I would prefer coarse/fine adjustments (or direct-entry via buttons) over turning a knob multiple times to make a larger adjustments.
  • I haven't needed to work on projects below 3.3 volts, but I am mindful of the pico-power AVR micros, which can run at 0.7V. Certainly a supply that can go below 1 volt would be useful for this.
  • A load switch is nice, but not a deal-breaker.
  • How essential is it to have separate earth ground? I don't think I need to combine power supplies.

Possible Supplies:

I've found a few supplies that I like, but I can't commit because none meet all the criteria.

  1. BK Precision 1550, 1-36V 0-3A, $150. Concerns: Doesn't go below 1 volt. Uses up/down buttons for adjustment.
  2. Circuit Specialists CSI3005X5, 0-30V, 0-5A, $130. Concerns: Unfamiliar brand and low price. (quality issue?)
  3. BK Precision 1671A, 0-30V 0-5A, $220. Concerns: Unknown adjustment turns; no earth ground terminal.

Is there some other supply or brand that meets all of these requirements? What points (if any) above, are truly important?

Best Answer

BK Precision 1550

This is a switching supply.

The up-down adjustments would make this a non-starter for me.

CSI3005X5

A whole bunch of companies re-brand this unit. They're actually fairly decent. The voltage pot is a 10 turn, the current limit is button-driven in 0.03A increments.

The most common resaler of the power-supply is MPJA. It also comes in a bunch of voltage and current ranges: 0-30V 5A, 0-60V 3A, 0-120V 1A.

One thing you can't see in the pictures is that the unit has a set of screw terminals in parallel with the output banana jacks, below the cover plate labeled "EXT OUTPUT". If you need more permanent connections, you can use the screw terminals.

The schematic for the whole supply is available. This makes it enormously more repairable (and hackable) then ANY of the others.

BK Precision 1671A

The funky extra output connections on this make me nervous (speaker terminals? really?).

I would guess that the potentiometers are single-turn, both from the artwork on the case near the knobs, and the fact that it does not mention multi-turn knobs, as that's normally a significant selling point at this price range.

On the whole, If I had to choose from the supplies listed, I would wholeheartedly recommend the CSI3005X5, more because the alternatives are considerably worse.

Anyways, I would say that even if you don't think you need a floating output power supply (what you really mean when you discuss a separate earth terminal), you almost certainly will find it useful in the future, so I think you shouldn't dismiss it. Just being able to string multiple power supplies in series for higher output voltages is tremendously useful.

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