# Considerations in a bench/lab power 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?

• Looking at MPJA's site, it appears they also rebrand some Meanwell power supplies that I am familiar with. Interesting. :) – JYelton Dec 23 '12 at 9:48
• Just to make your choices harder :-). Output switch is really nice to have - avoids having to pull out lead etc when testing. Fine control or multi turn on voltage highly desirable. Single multi turn pot only a hreat paid - usable if essential and better than 1 turn only. CC setting without shorting to set is nice but not essential. Cheapest of these sells for around $US35 retail in Shenzhen China (I bought some similar there recently) and maybe half that wholesale. Lean on them for price. – Russell McMahon Dec 23 '12 at 10:09 • Below 1.25V out (below eg LM317 level) is nice but if only used occasionally you can do with diodes and external voltmeter.) – Russell McMahon Dec 23 '12 at 10:10 • @Russell When you say cheapest of these, do you mean of the three I listed, or something else? – JYelton Dec 23 '12 at 10:13 • One thing that you may want to consider adding to your list of requirements later on would be a power supply with low output capacitance. If you're making a circuit and make an unexpected low impedance path somewhere, a power supply with high output capacitance will release large amount of energy when the capacitors are discharged (which will happen before current limiting starts working), which will probably burn the circuit you're making. – AndrejaKo Dec 23 '12 at 10:41 ## 4 Answers ## 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. • +1. Another use for bench supplies with floating outputs is to cobble together a split (+/- x Volts) supply for various circuits which need one, e.g. some op-amp based designs, some balanced output audio circuits, and so on. – Anindo Ghosh Dec 23 '12 at 10:34 • @AnindoGhosh - That too. – Connor Wolf Dec 23 '12 at 11:12 Here is the list of the generic china ones that are sold on Amazon under the names Mastech, Elenco, Sinometer and others.$185 Mastech TRIPLE LINEAR DC POWER SUPPLY 30V 5A HY3005F-3

• Dual adjustable outputs: 0-30V and 0-5A
• Fixed output: 5V and 3A
• Line regulation: CV <= 0.01% + 2 mV, CC <= 0.2% + 2 mA>
• Load Regulation: CV <= 0.01% + 3mV, CC <= 0.2% + 3 mA
• Display reading accuracy: +/-1% for voltage and +/-2% for current

Having the extra adjustable power outputs are convenient. They can be connected independently or in series or parallel to allow for higher amperage or voltage if needed.

The disadvantage is that the pots are all single turn, so it's hard to get very fine changes. Although you can replace them with 10 turn ones.

Also, the voltage and current displays come in LED (as shown in the picture,) or LCD.

As I mentioned in my other answer I have this one and it is pretty nice and the extra outputs come in handy.

$130 Sinometer HY3005D Variable Linear Lab Power Supply 0-30V 0-5A • Adjustable outputs: 0-30V and 0-5A • Input voltage: 110V AC and 220V AC switchable • Ripple noise: CV <= 0.5 mV RMS, CC <= 3 mA RMS Coarse and fine control for both current and voltage outputs.$80 Mastech HY1803D variable dc power supply

• Adjustable outputs: 0-18V and 0-3A
• Line regulation: CV <= 0.01% + 1 mV, CC <= 0.2% + 1 mA
• Load Regulation: CV <= 0.01% + 3mV, CC <= 0.2% + 3 mA
• Ripple noise: CV <= 0.5 mV RMS, CC <= 3 mA RMS
• LCD reading accuracy: +/-1% for voltage and +/-2% for current

Just a very cheap adjustable unit that doesn't take up much bench space.

• I have one of the Mastech Triple-output supplies. For the price, it's very nice. I particularly like the fact that is has LED readouts, rather then LCD readouts. However, the controls are only single-turn pots. I plan to replace the pots in my supply with 10 turn at some point. – Connor Wolf Dec 23 '12 at 11:15
• @FakeName Yah, I have several other supplies and I keep using this one. Next time I re-organize my desk I think this is going to be the only one I keep. I've been planning on changing the pots too, it's just a bit hard to hit an exact voltage. I'm surprised they didn't use 10 turn in the first place. – Garrett Fogerlie Dec 23 '12 at 11:20
• I have the mastec power supply and the only complaint is that it switches a lot between ranges. Otherwise it works nicely. So trying to sweep a range might not be a good idea, but for a variable steady supply it's great – Gustavo Litovsky Dec 23 '12 at 20:40
• @gl3829 which Mastec, the Triple Output one? I don't notice that, although you can certainly hear the relays changing taps, but the voltage seems fairly stable when it does so. – Garrett Fogerlie Dec 24 '12 at 16:16
• @Garrett: Yes. I haven't measured the voltage myself (I would need a scope to really see what is happening) but typically relays switching isn't that good. I'm happy to hear about the voltage being stable. – Gustavo Litovsky Dec 24 '12 at 17:36

I just order a KORAD KA3005P - Programmable Precision Variable Adjustable 30V, 5A DC Power Supply from Amazon.

I watched Dave's Review/FAIL video of it and then watched the follow up video and a follow up video by Charles Holtom from TrioSmartCal . For ~\$100 I thought it was worth giving it a try.

From SRA

Features:

• Compact Design
• Dual 4 Digit LED Displays
• Digital Controls
• Output switch control
• Switchable between 110v and 220v
• 4 sets of parameters can be stored inside for fast recall
• Keyboard Lock to prevent accidental changing of set parameters
• Circuit protection for over load, short circuit and over temperature.
• Automatic switching between mA and A display
• Quiet variable speed fan
• 2 Year Warranty!

Operating Conditions:

• Input voltage:110V +/- 10% switchable to 220V +/- 10%
• Frequency range: 50- 60Hz
• Operating temperature: 32- 104 F (0- 40 ºC)
• Operating humidity: < 80%RH
• Storage temperature: 32- 158 F (0- 70 ºC)
• Storage humidity: < 70%RH

Stable Voltage:

• Output Voltage Range: 0- 30V Continuously adjustable
• Setup Resolution: 10 mV
• Setup Accuracy: <0.05% +20 mV
• Ripple: < 1mVRMS
• Read back Accuracy: 10 mV
• Temp. Coefficient: < 0.1% + 10mV
• Read back Temp. Coefficient: < 100 ppm+10 mV

Stable Current:

• Output Current Range: 0- 5A Continuously adjustable
• Setup Resolution: 1 mA
• Setup Accuracy: <0.1% +3 mA
• Ripple: < 3mARMS
• Read back Accuracy: 1 mA
• Temp. Coefficient: < 0.1% + 5mA
• Read back Temp. Coefficient: < 100 ppm+5 mA

This power supply seems like it should be mentioned when considering a bench power supply.

• How did it work for you? Any drawbacks? – ergosys Jul 25 '13 at 23:30
• I've been using this thing for a while now. I'm finding that it has some issues. The 1st one was that the face plate fell off and I had to use some double sided tape to stick it back on. Now I'm finding that the power switch does not operate. If the PS is plugged in it is running. The power switch must be a soft switch and something is broken (mosfet, I assume). I haven't looked into fixing it but I am seriously looking at getting a different PS. – Hair_of_the_Dog Aug 6 '13 at 22:22

If you don't mind something old, and affordable, a Tektronix PS503, or two, or three, or four, in a TM50x mainframe fits the bill perfectly. Two channels, 20VDC each, can be put in series, current limiting, no overshoot on turn on, control down to zero, ground available, regulated, ... Everything you asked for. And you can add a DM50x to monitor it with backplane connections to economise on front wiring.

• The one glaring thing the PS503 seems to be missing is some sort of indicator as to the currently set voltage and current. I'd like to just have a single benchtop unit, if possible. – JYelton Dec 23 '12 at 9:39
• @JYelton - If you stick a DM501 multimeter in the TM502/3, it then does have indicators. – Connor Wolf Dec 23 '12 at 9:59