Low-profile replacements for SMT electrolytics...

[[email protected]]

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.

 

[legg]

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!

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

 

[[email protected]]

The original part was never low-esr.

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...

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

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

 

[Eeyore]

Hi,

I'm looking for the lowest profile replacement for a low-ESR 4u7 250V
SMT cap

What was wrong with the original ?

Graham

 

[Eeyore]

Low enough for reasonable performance and better than most
alternatives. That was a few years ago - there are almost certanily
better alternatives now

Better for WHAT exactly ? Your EGO ?

Graham

 

[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.

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

 

[[email protected]]

....

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

 

[legg]

...

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.

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