Nichicon UPJ for switching power supplies - what's so special about these caps? - Page 1
Forum section: electronics / projects

author: mightyohm
author_rank: Regular Contributor
timestamp: April 23, 2024, 03:52:43 am
content: 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.

author: Konkedout
author_rank: Frequent Contributor
timestamp: April 23, 2024, 04:07:03 am
content: 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.

author: mightyohm
author_rank: Regular Contributor
timestamp: April 23, 2024, 11:16:32 pm
content: 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.

author: wraper
author_rank: Unknown
timestamp: April 23, 2024, 11:33:13 pm
content: 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.

author: kimballa
author_rank: Contributor
timestamp: April 24, 2024, 04:09:07 pm
content: 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..

author: mightyohm
author_rank: Regular Contributor
timestamp: April 24, 2024, 10:25:43 pm
content: I was curious if there was a specific characteristic of the UPJ that made it particularly suitable for switching power supplies, and whether that would imply a tradeoff to using the same caps in other applications. It sounds like it may be just marketing. Would love to hear from someone at Nichicon regarding this but they have ignored my request.Regarding stability, it sounds like it is not a concern in this particular case.

author: Someone
author_rank: Super Contributor
timestamp: April 24, 2024, 11:11:29 pm
content: Quote from: wraper on April 23, 2024, 11:33:13 pmPerhaps you'd like to support a recent design I had where an LM337 and LM317 oscillated unless the MLCC outputs had damping added. They can and do oscillate.

author: thm_w
author_rank: Super Contributor
timestamp: April 24, 2024, 11:27:15 pm
content: Quote from: mightyohm on April 24, 2024, 10:25:43 pmIts reasonably well explained at the top of the datasheet:https://www.nichicon.co.jp/english/series_items/catalog_pdf/e-upj.pdf-Low impedance and high reliabilitywithstanding 5000 hours load life at +105˚C (3000 hours for smaller case sizes as specified below).- Ideally suited for use of switching power supplies.But yes, these topline quotes are generally marketing focused. If you see an opamp that says "for oscilloscopes" that doesn't mean you can't use it elsewhere, just means it has some properties that are useful in that specific scenario. Or "automotive" grade is another one, it meets automotive spec (wide temperatures, reliable, etc.) but you can freely use it for other designs.

author: bdunham7
author_rank: Super Contributor
timestamp: April 24, 2024, 11:38:31 pm
content: Quote from: thm_w on April 24, 2024, 11:27:15 pmThen there's "audio grade"...Ideally suited for first class audio equipment where qualitative and quantitativecomfortableness is required.https://www.mouser.com/datasheet/2/293/e_ukz-1513448.pdfSo many people love Nichicon for whatever reason, but they had capacitor failures in the plague times just like the cheap brands. And they have a high degree of market wankery. They're not my go-to brand at all.

author: wraper
author_rank: Unknown
timestamp: April 24, 2024, 11:43:35 pm
content: Quote from: bdunham7 on April 24, 2024, 11:38:31 pmStupid tax grade.

author: thm_w
author_rank: Super Contributor
timestamp: April 25, 2024, 12:24:08 am
content: Quote from: bdunham7 on April 24, 2024, 11:38:31 pmlol, 100% marketing in that case. I'm sure someone has figured out what series they are identical to, but they hide info from the datasheet.Here is the UFG series tagline: "Rich sound in the bass register and clearer high end, most suited for AV equipment."

author: wraper
author_rank: Unknown
timestamp: April 27, 2024, 05:05:18 pm
content: Quote from: thm_w on April 25, 2024, 12:24:08 amThe best part in these is to write some vague fluff yet provide zero measurable specification difference compared to "usual" capacitors.

author: Konkedout
author_rank: Frequent Contributor
timestamp: May 20, 2024, 04:08:32 am
content: Quote from: wraper on April 23, 2024, 11:33:13 pmI have been designing power supplies for > 40 years. This does not particularly make sense. A linear regulator (whether or not it is a low dropout type) may or may not be designed to operate properly with low ESR capacitors. But...LDOs are a bit newer than other regulators, and small multi-microfarad low ESR capacitors are also a bit newer.The only way to resolve this is to read the datasheet. But understand that when an LM317 or 7805 linear regulator datasheet was originally written, there was little or no such thing as a 10 uF low ESR capacitor so the datasheet did not caution accordingly.So far as stress is concerned, that concerns mostly ripple current. This is related mostly to the input or output pf some switching converters which create high ripple current. It is not likely to be an issue when using a linear regulator to drive almost any load that would make sense (in my opinion.)

author: jitter
author_rank: Frequent Contributor
timestamp: May 20, 2024, 05:22:30 am
content: Agreed. When I still worked in the electronics industry, I came across a flawed design using the LM317 and LM337 for positive and negative voltage regulation.In redesigns, the PSU section had been carried over unchanged and these things had worked as intended for decades. All of a sudden, in a particular batch of PCBs, I saw myself confronted with oscillating LM337s. All components placed were as per the BOM, so no errors there.Long story short: all this time the design had been marginally stable, but until then, had never posed a problem. However, now the usual tolerances - or combination of - caused oscillation. The flaw was quickly remedied by the customer's designer by putting a low ohm resistor in series with the LM337 output pin.The datasheet of the LM337 doesn't mention ESR at all, only capacitance ranges in which stability is guaranteed.

author: wraper
author_rank: Unknown
timestamp: May 20, 2024, 08:28:26 am
content: Quote from: Konkedout on May 20, 2024, 04:08:32 amThe difference with LDO is that high dropout regulators as LM317 and 78xx have emitter follower on the output, therefore they are inherently more stable. LDO have collector/drain on the output and are unstable with low ESR, especially early ones such as LM1117, unless datasheet explicitly says low ESR is fine. Negative regulators like LM337 and 79xx are not as stable for the same reason.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 20, 2024, 11:27:56 am
content: Good reading about the subject:https://www.ti.com/lit/an/snva020b/snva020b.pdf