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Nichicon UPJ for switching power supplies - what's so special about these caps?

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Nichicon markets the UPJ series "for switching power supply". Is there a downside to using this family of caps for general purpose filtering/bypassing, for example at the output of an LM317 or LM337?

The capacitors I am replacing are obsolete Nichicon PL series caps that leaked all over the PSU PCB in my Sencore VG91 test pattern generator. I found a datasheet for the obsolete PL family and the UPJ caps appear identical on paper, however I believe that Nichicon suggests the UPM family as replacement for PL. I'm not sure that a ripple rated cap is even necessary in this circuit, but for some reason Sencore used them so I figured I would do the same.

I'm also struggling to understand why there are so many low ESR/ripple ratedcap families with nearly identical specs and case sizes: UPJ, UPM, UHD, etc. I know that most of these are being obsoleted so I guess I should feel fortunate that I can still buy them at all.
The specs for the UPJ and UPM versions of the cap I need are very similar, but neither is identical to the PL. I suspect that either will work as a substitute, and I'm also tempted to just stick an ordinary UVZ in there because I don't think the ripple rating really matters.

Back to the original question, why would a capacitor be specifically rated for switching PSU use, what makes the UPJ any better than any of the other low ESR families, and is there a downside to using UPJ in other non-switchmode applications?

I tried reaching out to Nichicon - no response.

I have not been surveying the electrolytic capacitor market so much for the last few years, but most of what has happened has been an evolutionary physical downsizing.  Better performance in a given case size.  I did design power supplies using PL types when they were new, but I think that was 25 - 30 years ago.

Thinking about it, there is not so much use for larger sized electrolytic capacitors OTHER than a power supply.  In most cases I think that lower ESR is better and does not have a lot of risk, but:

1) Some linear regulators (particularly older ones.  The LM317 is certainly older) require ESR in their output capacitor so as to insure stability.  The difficulty is that many of these were designed before a 22 uF ceramic capacitor was reasonably available, and all aluminum and tantalum electrolytics had considerable ESR.  Now there are the bigger value ceramics as well as polymer types and low ESR electrolytics.  You really do need to dig into the regulator spec sheet.  Or another approach is to model it accurately with a good simulator.  Maybe TINA-TI has a good LM317 model.  Of course you would need to include the capacitor ESR in your simulation.  Or else, try it in hardware and do SOMETHJNG to test out the stability of the regulator.  The easy but less rigorous approach is to apply a pulse load and look for ringing in the output voltage waveform.

2) Once upon a time I did a blanket change of a manufactured power supply design and changed a small electrolytic capacitor (maybe 4.7 or 22 uF) from a standard type to a low ESR type.  The power supply then did not work with this change.  This is unusual but it does happen.

Thanks for the warning about stability. The board came with PL series caps, which are fairly low ESR. I figure that as long as I keep around the same ESR (and capacitance) I should be fine.

LM317 is not an LDO and therefore is stable with low ESR capacitors such as MLCC. UPJ series have low ESR and high ripple current rating. Therefore they can survive way more load/stress than general purpose capacitors.

I don't think in most cases you need to find the exact same capacitor for a replacement. If it's not super sensitive test equipment, any matching spec usually will do. There's a lot of manufacturers and lots of marketing claims about what applications each model is good / designed for - but I think a lot of that is just SEO so engineers steer their way when looking at a giant catalog of otherwise identical parts.

Capacitance, ESR, Tolerance, max voltage, max temperature, and physical dimensions (especially height).

If it is equal on capacitance and tolerance (virtually all electrolytic are 20%), "similar" esr, and same-or-better voltage and temperature handling and it physically fits on the board / in the enclosure, you're probably good..


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