Low-profile replacements for SMT electrolytics...

Hi,

I'm looking for the lowest profile replacement for a low-ESR 4u7 250V SMT cap - currently I'm using a Nichicon UUJ2W4R7MNR1ZD, but that it quite high - I'd prefer something far lower profile, maybe less than

5mm, or two or three devices in parallel. the low ESR bit is very important, as is the 220V+ voltage rating - its part of an SMPS.

Sensible ideas gratefully received!

Ta.

Reply to
nick
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The original part was never low-esr.

What is your priority; reduced loss or low profile? None of this 'prefer' stuff. What do you or the circuit actually need?

RL

Reply to
legg

Low enough for reasonable performance and better than most alternatives. That was a few years ago - there are almost certanily better alternatives now, hence my question - I've not found any obvious replacements though...

The existing component works fine, but I'd like a lower profile, preferable 5mm or less, which is dificult with an Al electrolytic. A couple of smaller devices in parallel would help the final ESR and may lower the profile - are there ceramic alternatives?

Its in the output smoothing of an SMPS, so good ESR is a prerequisite.

Thanks

Reply to
nick

What was wrong with the original ?

Graham

Reply to
Eeyore

Better for WHAT exactly ? Your EGO ?

Graham

Reply to
Eeyore

If the original circuit works fine, then you do not 'need' low esr, but only the 4.7uF / 10-50R ESR performance of the original.

If you could indicate required ripple current (rms and peak @ Fapp), operating voltage, temperature range and permitted ripple voltage, a lower capacitance or combination of smaller parts (electrolytic and ceramic) might possibly allow reduced profile and improved performance.

250V and 500V smd ceramics are available, but they carry signifigant cost (dollars per each)and processing issues (body size and cracking). Though possibly lower in profile, they will consume considerably more real estate than is currently allowed.

Kemet 'Sierra' smd parts approach 0.75 inches in length, for a 2.2uF

500v example in X7R dielectric.

A 250V 1uF part from Murata might measure 0.2 inches square, and suffer from 50% capacity reduction near it's labelled voltage.

SMD film parts are interesting, but are not for adoption by the light-of-heart, particularly in Pb-free reflow environments.

RL

Reply to
legg

In the layout for those parts at minimum, you could add a "field plate" on each side of the PCB,one connected to the + side, the other connected to the - side; that added capacitance, if sufficent, will bypass the resonances of the SMT caps and help reduce the ESR...

Reply to
Robert Baer

On Sep 10, 11:50=A0pm, legg wrote: ...

Thanks for your comments - the object of my search is to reduce the height of the SMPS output smoothing capacitor - some of the other respondants obviously missed (or chose to miss) that point ;-)

It seems that there may be no easy option - I can afford some more horizontal real-estate - its the height I want to reduce as I want to use a very slim housing for this and the cap is the tallest component by far on the PCB. Output ripple is not critical - I'm drawing maybe

10mA @ 200V from the SMPS, and the downstream devices are not sensitive to a few % ripple. With the existing cap, the SMPS runs at approx 87% efficiency - it'd be nice to improve that, but its not necessary and way down the list - physical size is the issue.

Cheers

Reply to
nick

--
http://www.google.com/search?hl=en&rls=GFRC%2CGFRC%3A2006-50%2CGFRC%3Aen&q=low-profile+high-voltage+electrolytic+capacitors&btnG=Search

will get you about 24,000 hits, so there may be something there you can
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Reply to
John Fields

At present, most of the ripple in your circuit is actually due to the electrolytic's ESR - which will be in the region of 10-50R - a typical value for small high-voltage electrolytics. Depending on the mfr's thermal impedance model, the ESR of the actual part used is 47R (200mW) to 118R (500mW). There is a lot of competitive fudging going on where ripple current ratings for small electrolytic packages is concerned.

Even assuming a minimum operating frequency of 20KHz and the peaky-est converter topology, the actual required capacitance to provide this kind of ripple at 10mA is less than 0.1uF.

If you don't have access to the original design notes for this circuit, you may not be in a position to determine what the design factors were in selecting the original 'oversized' part.

My suggestion is tha you try 0.1uF X7R 250V in parallel with: {a network of .47uF X7R 250V in series with 50R 350mW}, over the entire load and operating temperature ranges required - while examining turn-on, turn-off and stability performance of both the converter and the system in which it is used.

None of these alternate components is particularly expensive, and all have a low profile. The total component cost WILL be higher, and the real estate consumed will ~double, but if your testing and observations allow it, you will have achieved your intended magic trick.

RL

Reply to
legg

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