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I'm building a small regulator for a project I'm working on, and I happen to need 12VDC for the main application, as well as a 5VDC rail for powering a Raspberry Pi 3 and some shift registers. Since the 5 VDC rail is going to consume around 3-4 A I thought burning of the unnecessary voltage with a linear regulator was a bit too excessive, and since space is at a premium, I decided to go with a commercially available DC/DC converter.

The converter I chose is the following from Delta

The datasheet isn't the worlds greatest, but so far I've been able to deduce the following:

  1. I need a resistor for the trim option to select the appropirate output voltage
  2. A Low ESR output capacitor is needed to smooth out the ripple
  3. The Output Enable can apparently be left floating if not needed

However, what I can't really get my head around is if I need some sort of input capacitors as well (they've spec'ed the suggested minimum input capacitor as OSCON 16V/270µF (ESR 18 mΩ max.)), the datasheet has some mention of a 100nF ceramic and a 10uF tantalum capacitors, but I can't tell if it's only for some measurement setup?

Also, the capacitor they've spec'ed (OSCON 6.3V/680µF (ESR 13 mΩ max.)) seems to be rarer than hens teeth, so I'm thinking of substituting it with this capacitor.

Am I missing something else?

The whole board will be fed from a Meanwell 12VDC PSU.

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Regarding

1: Yes! you do need a trim resistor to set the output voltage on this supply, given that you want 5VDC you should put a 287 ohm resistor connected from trim to ground as per figure 27 and 28

2: Definitely you need an output capacitor, for what i can see the supply has no output filter capacitor, so yeah, it's basically indispensable. I would put a 100nf and 22uf ceramic in parallel with the alternative 680 one you suggested, just be sure to choose ceramics with a voltage rating a few times greater than the output voltage (for more info look for voltage derating on class 2 ceramic capacitors)

3: yes you can leave it floating no problem

regarding the input capacitor you definitely need one if you wish to pass any compliance test, they mention multiple capacitors (big electrolytic, small ceramic and tantalum) because they resonate at different frequencies, hence the 100nf for example is better at decoupling higher harmonics than the electrolytic ones (same reason why i suggested you do the same at the output).

regarding the tantalum, i would avoid them, you can put a big ceramic one which will yield a very low esr and enough capacitance if dimensioned properly, plus you will reduce the amount of conflict minerals on your design and eliminate the chance of your tantalum blowing up when connected to low impedance sources

also you can put a ferrite bead in the input if you want to reduce emi even further but that's not really necessary

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  • \$\begingroup\$ Cheers mate, now I get what they were hinting at. As for the input capacitance, would 270µF electrolytic, 100nF ceramic and 22µF ceramic be good choice? I'm aware of the tantalum's tendency to explode at certain times, hence I rarely use them. I'm not really worried about passing any compliance, this is for a clock that will hang on my wall in my garage, but I might as well get into the habit of doing things "properly" :) \$\endgroup\$ – Stuggi Apr 15 '20 at 21:55
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    \$\begingroup\$ I think it would be good indeed \$\endgroup\$ – diegogmx Apr 15 '20 at 21:58
  • \$\begingroup\$ Just finished the soldering my PCB for the PSU module, turned out great, the 5VDC has around half the ripple of my B&K bench power supply, so I'm happy! Thanks for the help mate! \$\endgroup\$ – Stuggi Jul 25 '20 at 8:45

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