Constant Current Power Supply

I need a power supply that can deliver a constant current by automatically varying the voltage as the resistance changes. It must not use PWM. What kind of PSU would that be?

How many amps? Voltage limits?

Take a look at the backlight circuit on our display boards.

are you talking about a benchtop PSU or a chip or a module?

I take it that no PWM means you font want a switched mode supply. Can I ask why not?

You can use an LM317 and a resistor as a current source; it’s not efficient, but it works.

@ Gus, I’m thinking 2 amps, limited to 12 volts.

@ hagster, a benchtop PSU

@ godefroi, an adjustable regulator that tolerates more than an amp, but how do I make it adaptive due to the slowly changing resistance of the load.

You probably want a PSU with ‘Current Limit’ feature. You just dial in the current you want and wack the voltage up to the max level you require. I use this to charge LiPo batteries sometimes. Just put in 4.1/4.2V and set the max charging current and it automatically switches from constant current to constant voltage.


Normally the ADJ pin for an LM317 is set to somewhere between VCC and GND which sets the output voltage.

In a constant current configuration, you tie ADJ to the load through a resistor.

@ godefroi - Oh, I get it.

@ Mr. John Smith - Make sure you select an LM317 model that can handle your current requirements

For someone who messes around with electronic stuff a good bench supply is a no brainer.

You can get good ones with dual channel and 0-30 volts with 0-3 amps for good prices these days. The current limiter on these can save your designs if there is a fault. Lots of people play with the ATX power supplies but those suckers can generate huge amps with very little protection.

The advantage with the bench supply as Hagster indicated is that they can double as constant current outputs too.

Since this thread is a year old and there weren’t many links on it, I’m going to ask it again since I’m looking to buy a current limiting bench supply. The Maplin one looks perfect but I wonder if there is one closer to the U.S. that others can recommend.


What is your budget Ian? are very good service and they offer good prices and in the US. Also, if you join the eevblog forum you can ask for the discount code. :slight_smile:

I recently bought a GW Instek GPS3303 as I like the fact you can set the voltage and current and then switch the output ON and OFF. Much better than either adding a switch yourself or powering on and off the supply.Price was also very good value. Around $200 I think it was.

I was thinking $100-$150 should get a decent single output supply. I could be talked into spending more if there’s a good reason. I also like the idea of finding a nice thin single output supply that I could buy multiple of as I decide I need more outputs. This seems like a safer, more flexible option than paying 2-3 times for a single 3-output supply. Is there a benefit to having all outputs in a single box? Price seems marginal.

Thanks for the link. Exploring now… I found the eevblog code but can’t figure out how to apply it at Do you know what discount it provides?

That model appears to be discontinued now and replaced with the GPE-3323 ($310.50). A very nice supply but perhaps more than I want to spend right now.


did you find a power supply? Just curious as I’m looking as well.

@ mikef - I haven’t ordered one yet. I got past my immediate need so the urgency has gone but I still want to get one. I’m thinking about trying out this Tenma 72-8345A. Does anyone have any experience with it?

I like the size of that one.

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Yea, me too. And it will be easy to put several side-by-side if I decide to add more later.

Handy for sure but a dual channel model is better as you can parallel up the outputs or serial them to give higher current or voltage. They have this built in through simple button selection. Only downside I don’t like that you need 4mm banana plugs to use it. They don’t have the normal screw terminal posts.

I like that one though as it has 3 decimals on the current. My GPS-3303 is only 2 but my old TTI PM330QMD has the 3 and it does make a difference when working on low power devices.I wonder if they have a dual version with the same 3 digits.

Tenma is quite a nice make. Element14 here offers their stuff and normally they only offer decent quality makes too.

I’m not seeing many dual channel < $300 let alone with 3 decimals on the current.

Nearest I could find is this one but still not $300 or less.