Oscon dangers???

[Htguy]

Hi,

I have been looking into using Oscons to replace power filters in digital circuits, but after reading the Sanyo warnings page for oscons they warn about very hugh initial charge, and post turn off discharge rates. (Due to the very low esr of oscons)

I am wondering if anyone has experience with going overboard in swapping out regular smd electrolytics for oscons? (I know a lot of DIYers live by the motto Bigger is always better, but it seems just to replace with the ssame value oscon could really damage a chip/circuit.

You can get the operating precautions info by clicking the link on the following page and down loading the .pdf titled operating precautions (Or you can download the entire line info {2.1MB} for more complete explaination of inpact of using oscon

http://www.secc.co.jp/english/produc.../download.html

Thanks for your thoughts.

God bless...

Mark

[poynton]

Originally posted by Htguy
Hi,

I have been looking into using Oscons to replace power filters in digital circuits, but after reading the Sanyo warnings page for oscons they warn about very hugh initial charge, and post turn off discharge rates. (Due to the very low esr of oscons)

I am wondering if anyone has experience with going overboard in swapping out regular smd electrolytics for oscons? (I know a lot of DIYers live by the motto Bigger is always better, but it seems just to replace with the ssame value oscon could really damage a chip/circuit.

You can get the operating precautions info by clicking the link on the following page and down loading the .pdf titled operating precautions (Or you can download the entire line info {2.1MB} for more complete explaination of inpact of using oscon

http://www.secc.co.jp/english/produc.../download.html

Thanks for your thoughts.

God bless...

Mark

Hi.

I read on another thread recently (posted by Elso - I think) that Oscons and other very low ESR caps should not be used at the output of regulators, presumably because of the inrush current. At switch-on, the cap would appear as a dead short !!!

Reading the pdf files, it would also appear that problems could occur if an Oscon was parallelled with other caps as smoothing, pre-regulator, since they would 'grab' the lion's share of the ripple !

So, my reading of the situation is as follows :-

Oscons should only be used in low ripple current circuits.

Oscons should not be used immediately post regulator, unless a slow startup is used.


Which does lead to the question :-

where should they be used?


Andy

[Bobken]

Hi,

I haven't read the Oscon 'reference', but I think you will find that the advice not to use Oscons directly at the outputs of some regulators is (usually) for an entirely different reason.

Because of their extremely low ESR at HF, it is often recommended to add a low-value resistor in series with the output cap, to help prevent any potential oscillation which could otherwise occur.

The biggest problem I found with Oscons, and I did use quite a few some years ago, is their very low voltage ratings generally, IIRC with about 25v max. here.

It may be that some users have attempted to go beyond the safe usable voltages, as this would very likely cause some problems in use, and manufacturers will always tend to err on the side of caution as they naturally don't want any 'come-backs'.

Blackgates have even lower ESRs, and I have never experienced any problems in use with these. Incidentally, good regulator designs will usually have some diodes (or will recommend using these) to avoid the output caps from discharging back through the regs at switch-off, but it is dangerous to assume this without checking.

Regards,

[Elso Kwak]

Originally posted by Bobken
Hi,

I haven't read the Oscon 'reference', but I think you will find that the advice not to use Oscons directly at the outputs of some regulators is (usually) for an entirely different reason.

Because of their extremely low ESR at HF, it is often recommended to add a low-value resistor in series with the output cap, to help prevent any potential oscillation which could otherwise occur.


Regards,

I agree with bobken. It's not an inrush current problem.

[poynton]

Originally posted by Bobken
Hi,

I haven't read the Oscon 'reference', but I think you will find that the advice not to use Oscons directly at the outputs of some regulators is (usually) for an entirely different reason.

Because of their extremely low ESR at HF, it is often recommended to add a low-value resistor in series with the output cap, to help prevent any potential oscillation which could otherwise occur.

The biggest problem I found with Oscons, and I did use quite a few some years ago, is their very low voltage ratings generally, IIRC with about 25v max. here.

It may be that some users have attempted to go beyond the safe usable voltages, as this would very likely cause some problems in use, and manufacturers will always tend to err on the side of caution as they naturally don't want any 'come-backs'.

Blackgates have even lower ESRs, and I have never experienced any problems in use with these. Incidentally, good regulator designs will usually have some diodes (or will recommend using these) to avoid the output caps from discharging back through the regs at switch-off, but it is dangerous to assume this without checking.

Regards,

I can see that a low value resistor would damp oscillations but whats the point in using a low ESR capacitor and then adding resistance ?

[Elso Kwak]

Originally posted by poynton



I can see that a low value resistor would damp oscillations but whats the point in using a low ESR resistor and then ading resistance ?

Also agreed, LOL
Your design must be compatible with Oscons!

When far away from the regulator as in the Sony SCD-1 the Oscons were placed at the IV-converter ICs and it worked well.

[Bobken]

Hi,

There has been quite a lot of discussion on this particular issue on the Forum in the past.

I expect you would find this counter-intuitive, and this is understandable, but a search should provide you with some bedtime reading!

Regards,

[Bobken]

Hi,

In the case which Elso has just cited, the necessary HF impedance to avoid potential oscillation here, would probably have already been provided by the wires' inductance.

[Htguy]

Hi Everyone,

Thanks for the info, it is very helpful. I am just curious if anyone knows the ERSR of Blackgates and Cerafine caps? Someone said that blackgates have a lower esr than oscons?

[Bobken]

Hi,

Regrettably, I have thrown out all of my data on Cerafines and Oscons, as I no longer use these caps out of choice. Having used them (and Silmics) for many years, I am familiar with their general characteristics in use, though. I am sure there must be lot of info. on the 'net, if you do some searches on this subject.

Without spending hours in research, all I can quickly find on Blackgates is the following, which is not very spectacular, it must be said. Jelmax claim 156 mOhm with a pair of 220uF x 6v3 BGNXs at 100kHz, used in their recommended "Super 'E' configuration".

However from several graphs which I have seen, what was more significant was that the BG ESR graphs continued downwards in an almost linear fashion, all the way up to 1Mhz. Others I have seen will inevitably 'turn back' at some point, possibly well prior to 100kHz even, and the curve shoots back upwards at VHF to very much higher figures again.

Whether these figures can be believed, I will not speculate as there have been too many arguments on the Forum in the past about this subject. I have never measured any caps' ESR for myself.

If it helps, I used to use Cerafines for many years, all over the place, and 'subjectively' found them to be good. Later on, when Oscons became available, I found these to be better in certain situations (especially digital), and then later still, I tried BGs, which were (generally) even better than Oscons in analogue circuits, and most digital locations too. I don't wish to say any more about this as it has been such a contentious subject before, but I would not choose to go back to previously-used types of caps, nowadays.

From your query's point of view, though, I have never (yet!) experienced any problems along the lines of your initial concerns, and I have been 'swapping' components for some 35 yrs. now, in every audio location (analogue and later on in digital circuits) you can imagine.

IHTH.

Regards,

Edit: Maybe I should have said that I have needed to replace diode bridges on occasions, due to the higher initial inrush current at start-up with using both lower ESR caps, and using increased values of caps here.