Project files: Filtered IRM power supplies (part 1)

As promised a while ago, here are my designs for the “filtered” power supplies based on IRM AC/DC modules. These are excellent for adding compact and powerful single and dual supplies which still have a reasonably good performance to any small preamp/headamp amplifier.

What is it?
Small single-/dual power supplies with IRM AC/DC power modules from Mean Well and passive filtering. The IRM modules are coupled with C-R-C or C-L-C “Pi”-filters, which should reduce the ripple on the output quite significantly due to the high switching frequency of the IRMs. There are single and dual versions for both the 5-10W and 15-20W IRMs, so four boards in total. I also have various other combinations (IRM and filter on separate PCBs etc.) which I expect I’ll be posting in a future post.

How big are the boards?
The 5-10W boards are 1.05”/2.1” x 3.6” (app. 27/54 x 92 mm.) for the mono/stereo versions respectively.
The 15/20W boards are 1.25″ x 3.55” (app. 32 x 90 mm.) for the single version and 2.2” x 3.9” (app. 56 x 99 mm.) for the dual version.

What is the status of the boards?
All these are version 1.0. They have all been tested and work as expected (although I have no measurements confirming the efficacy of the filter).

Does it use any special/expensive/hard-to-find parts?
No. You can get the IRM-modules from many sources such as Mouser, reichelt, TME etc. and they should not be very expensive. There might also be similar AC/DC-converter boards from other manufacturers such as Recom, Traco etc. that could be used instead, but to be honest this time I could not be bothered to look for substitutes. As series inductors I’ve used the AIAP-03 series from Mouser or something similar from Reichelt (search for 77A), but there should be many of options available.

Anything else I need to know?

  •  I can’t find anything about the maximum permitted capacitive load for the IRM-modules, but I’ve tended to stick to low-ish values such as 220-680uF (1000uF in one case) and that did not seem to cause problems. Again, with a very high ripple frequency even a low value capacitor should make a big difference on the output.
  • Remember to calculate the voltage drop and power dissipation in the series resistor/inductor for at least the load current that your circuit draws at max. Ideally, you also calculate for the max current your IRM-module is able to supply to ensure that an accidental short somewhere isn’t a going to be a problem.
  • If you are using the 24V version of the IRMs, remember to watch the current (and power dissipation) in the LED resistors – unless of course you use resistors that are rated for more than 1/4W.
  • There is no BoM included for these because that really should not be necessary.

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.

26 Responses to Project files: Filtered IRM power supplies (part 1)

  1. Neal says:

    Hi,
    Thanks for uploading this. I know you say there reall is no need for a BOM, but I’m having trouble with the pi filter. I’ve read about the calculation (eek!) and have found calculators such as http://www.calculatoredge.com/electronics/ch%20pi%20low%20pass.htm, but I have no idea what values to put into the boxes. In one of your other posts on these, you mention the switching frequency of between 66-100kHz, for example, but I can’t even find this on the datasheet. I do try and find most things out for myself but I’m really struggling with this. I’m trying to use this for a raspberry pi with HAT so using 20-5.
    Thank you

    • theslowdiyer says:

      To be honest I’ve never really bothered with the calculation of the noise reduction on the pi filter (especially for CLC-filters), but just worried about the DC-voltage drop and power dissipation in the series element to ensure nothing is overloaded. For that you obviously only need Ohm’s law. For noise reduction the calculated noise/ripple reduction is so high that I don’t really trust it so I would measure it instead.
      For inductors I’ve basically looked at DCR (for voltage drop/power dissipation) and then gone for the biggest inductance i could get in a given form factor. I think you can sim pi-filters with http://www.duncanamps.com/psud2/ but as I don’t have a PC that will run it I’ve never tested it myself. The switching frequency of the IRMs is on page two of the datasheets next to the block diagram for the PSU (stated as Fosc) by the way.

  2. Enjon says:

    Thanks for the reply. Can you tell me if I’m on the right track? I’m looking at the datasheet for the AIAP-3 inductor and I choose an inductor first on current draw, presuming that I would need a minimum of 1A for a Pi 3 and I2S HAT with no other peripherals. I then try and figure out the correct inductor impedance by trying the highest impedance value and checking the voltage drop using the resistance of the inductor (DCR) and Ohm’s law with the aim of keeping the drop as low as possible by using Ohms law.

    (BTW, it took me ages to find the switching frequency, even after you pointed it out!)

    Apologies for the convoluted message, as you can see, I have a very limited understanding but hopefully every time I try something, I learn something.

    • theslowdiyer says:

      Yeah, I’d sort of forgotten that this is for a Pi – sorry. Normally you’d probably be sizing for a reasonable power dissipation in the inductor, but for a Pi the critical limitation is voltage drop because if the voltage to the Pi drops too much it shuts down. I’d try to choose an inductor that keeps the voltage drop below 0.2V at your max current draw (my best guess at what the Pi will tolerate, not tested or anything). If you expected max current draw is 1A, your max allowed DCR is 0.2 Ohms and of course the inductor has to be rated for more than the 1A max. current.

      As a safety precaution here I would either buy a couple of alternative value inductors to experiment with or pick a lower DCR to give some margin. For an AIAP-3 inductor I’d probably pick something like 100-150uH.

      Again I don’t think you’ll really know the difference between (say) 100uH and 150uH, so better safe than sorry. If you get it wrong, the most likely symptom is that the Pi resets when there is a power spike (e.g. when inserting a USB device) or refuses to start completely (because the power spikes at startup).

      • Enjon says:

        Thanks for that, very helpful and good to see it confirms I was heading in the right direction. I’ll take your advice with the alternative inductors and test. I think 1A should be enough, from what I can find the Pi draws about 700mA under a heavy load (such as 1080p video) and the GPIO draws 50ma max.

        Again, thanks for your help, this is one of the most useful (and helpful) sites I’ve come across.

        • Enjon says:

          Actually, the value I gave for the GPIO is for the older Pi boards, it should be higher on the Pi3 B+, but I can’t find a definitive answer. I can’t find any info on current draw from any of the HATS I’ve looked at either. Ah well, more searching.

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  7. Martin Nilsson says:

    Really like your psu designs!

    Im going to use it for a 12v standby psu for an arduino mega.
    You have designed your 15w modules as a dual setup but to power an arduino mega a single IRM-15-12 should be enough?

    • theslowdiyer says:

      There’s a single version board file in the .zip as well 🙂 The 15 and 20W modules are the same size, but in all honesty I would think that the smaller 10W version would be enough (if you need the space).

  8. Martin Nilsson says:

    Found it:)

    Im thinking of making it stackable, something like an arduino shield, so that modules could share mains input and the 12v output. Perhaps you have already thought of that?

    Is there a stackable pin header that can handle the mains input?:)

    • theslowdiyer says:

      I think there are, but I don’t know any specific part numbers. I am thinking Mouser’s catalogue is a good place to start searching though? I didn’t really think about stacking anything here because normally I want to be able to fit modules into a 1U enclosure if at all possible 🙂

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  12. Simao says:

    Hi there. I’m a complete noob in here. I’ll be using your design to power a phono stage.
    Thing is I don’t know the values for the parts.
    I will be using a IRM-20-24, can you give me some guidance on the capacitor values and inductor?
    From what I’ve read capacitors from 220 to 680uf will be fine, but what voltage?
    I really need a stable 24v PSU.

    Thanks in advance.

    • theslowdiyer says:

      Consider it an opportunity to learn some basic theory then 🙂 If you are using a 24V module, then of course your capacitors need to be able to withstand that voltage, so 25V or higher. As for choosing the inductor you want the highest possible value that is still rated for the max. current draw and doesn’t give you an excessive voltage drop. What that means is you need to first of all know the current draw of the phono stage. Also, please be aware that I haven’t tested the IRM PSUs with a phono stage so it’s hard for me to guarantee that it is quiet enough for that use.

  13. Simão Lopes says:

    Thanks for your reply!

    That voltage makes perfect Sense.
    I’ve been Said that my circuit takes no more than 5w, so I have to choose an inductor acordingly to this right?

    • theslowdiyer says:

      Measurements are better than hearsay 🙂 5W at 24V is roughly 200mA, so at minimum that’s what the inductor must be able to handle. For a bit of additional safety, consider choosing an inductor that can handle the worst-case current, i.e. the app. 1A that the IRM-module is able to provide. Not strictly necessary, but will ensure that the inductor isn’t damaged if e.g. there is an accidental short of the power supply.

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