smd CRC filter

Nikitas

Member
2011-11-11 9:13 am
I' m currently redesigning a psu for my f5 turbo, and this question popped in my head: has anybody tried a smd crc filter?
should I have any decent expectations? Even in theory, would the quality and performance be comparable to a through hole linear psu?
 

Nikitas

Member
2011-11-11 9:13 am
Hi All

The PSU i'm trying to substitute is a bipolar +/-32V with total 14 [email protected],47ohm and 8 caps [email protected] per channel.

Andrew, Resistors are no problem, with caps there is one.

Now, with caps the problem is that I can find 10.000uF electrolytics but they go as far as 12V.
Or I can find caps rated @35V but the highest capacitance is 2200uF.

twest820, could you elaborate? I wrote some specs above, but I think I don't understand what do you mean by stopband rejection? If you mean what I think, then the highest possible would be my answer :)
 

twest820

Member
2009-06-24 10:49 pm
twest820, could you elaborate?
You're still a long way from clearly describing the application or what needs to be filtered how. Answering Andrew's power question would be a start, though one usually also posts a schematic when asking questions like this. Assuming the F5 Turbo you're referring to is this one and that it's all that's on the supply I doubt you need to be particularly concerned of parasitics. If you're thinking RCRCRCRC on each rail a 34kHz corner's probably not the greatest choice as the F5's a class AB load and the filter's passband is not necessarily wider than that of the source driving the amp. You'd probably be better off just regulating the control loop.

Not sure why you're having trouble finding 10,000uF 50V caps. As I'm typing this Mouser EU has 172 Nichion VRs in stock, for example.
 
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Nikitas

Member
2011-11-11 9:13 am
twest it looks like there's miscommunication.

If you don't know what the f5 is then simply ask me that.
I'm sorry if i took for granted that you know what an f5 is, but other than that I don't see any reason for your "tone".

I did answer Andrew's question. The cap you posted isn't smd package.

I'm thinking CRC.

I have no clue where you're going with this "If you're thinking RCRCRCRC on each rail a 34kHz corner's probably not the greatest choice as the F5's a class AB load and the filter's passband"

Here's the article about the f5: http://www.firstwatt.com/pdf/art_f5_turbo.pdf

My amp is the v2 and a few pages below you can see the schematic my thoughts are originating from. There is no numbering on the pages, so I can't guide you better than this.
 

twest820

Member
2009-06-24 10:49 pm
If the requirements for folks who take their time to try to help are to 1) be able to map a two word phrase to a load schematic (done with reasonable accuracy as posts 8 and 10 have the same link), 2) know the PSU schematic a priori (apparently it's first order RC, though the specifics of which caps go where, what the outputs are, and how it connects to the load remain unclear---one now guesses "a few pages below" refers to page 11 in the linked pdf, however), 3) know a priori what it is the filter needs to reject (still unclear, though the most likely target seems to be mains noise), and 4) be able to make high value SMD caps not currently available on the market (rather unlikely) then, yes, I do believe there are going to be some challenges. Not so much about communication but around expectations.

There's quite a bit of existing discussion on this forum about passive supply rail filters for various purposes, how they interact with load behaviour, and how bypass ladder selection affects the supply's output impedance. It could be worth spending some time connecting that with Spice models of your build and running some AC and transient sims. Doing so would likely alleviate some of the difficulty in describing what this supply is supposed to do. Good luck! Primary side mains filtering could be worth looking into as well.

I did answer Andrew's question.
This is incorrect as the power requirement for the filter resistors has not been stated. Nor can it be inferred with much precision until the supply outputs are indicated. Based on the information in this thread so far the resistors might need to handle 10+A. Or 10mA could be OK. I would tend to guess more the former, though, in which case the thermals for SMD will probably be a bit interesting. Depending on the layout and how the caps are used routing traces rather than resistors might be an option.
 
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I' m currently redesigning a psu for my f5 turbo, and this question popped in my head: has anybody tried a smd crc filter?
should I have any decent expectations? Even in theory, would the quality and performance be comparable to a through hole linear psu?

So the answer is...
1. Nobody tried a SMD CRC for F5 turbo, as no suitable SMD capacitors are out there for such duty, and use of SMD resistors in such application is nonsense. Well, use of SMD capacitors in same application is nonse too.

2. In theory, if you take all of it (production technology of SMD caps) it is impossible so far.


And a remark - electrolytic SMD capacitors are absolutly the same electrolytic capacitors, but their pins are bended sideways. So, there is no difference between SMD and regular electrolytics whatsoever.
 

Nikitas

Member
2011-11-11 9:13 am
So the answer is...
1. Nobody tried a SMD CRC for F5 turbo, as no suitable SMD capacitors are out there for such duty, and use of SMD resistors in such application is nonsense. Well, use of SMD capacitors in same application is nonse too.

2. In theory, if you take all of it (production technology of SMD caps) it is impossible so far.


And a remark - electrolytic SMD capacitors are absolutly the same electrolytic capacitors, but their pins are bended sideways. So, there is no difference between SMD and regular electrolytics whatsoever.


thanks.

So even if paralleling *more* caps one couldn't reach the desired result?

I don't think that smd resistors for such an application is nonsense when using appropriate configuration and even heatsinks. From the specs I see out there, resistors shouldn't be a problem.

So nobody even tried it?Maybe I'll be the first to find ways NOT to do it! hehehe :p


PS I liked my last line enough to use it as a signature ;)
 
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