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'[EE] Capacitor-divider powr supply problem'
2008\08\25@232347 by Electronic Elephant n/a

picon face
Hi,

Now my case using the capacitor-divider to generate a 9mA current for
payload.
This circuit can work fine, but the C1(0.47uF,630V) is too big to us.
It's volume is nearly: 29mm*13mm*20mm(height),
[image: http://91mcu.bokee.com/inc/AC-DC.bmp]
Now I found another capacitor on the TDK's website:
http://www.tdk.co.jp/tefe02/e415_ckg.pdf
Quote:
2-chip Piled Multilayer Ceramic Capacitors
CKG Series CKG32K Type
FEATURES
• No polarity.
• Twice the capacitance is obtainable on a single capacitor space.
• Unique construction provides high reliablity.
• The metal caps absorbs stress from thermal and mechanical
shocks, ensuring excellent performance on aluminum circuit
substrates.
• Low ESR and ESL promises excellent characteristics for high
frequency switching power supply.
APPLICATIONS
Smoothing circuits, temperature variable applications,
Maintenance free power supplies, DC to DC converters, automotive
applications.
it seems very small.

Now my problemis :Can I use it in my design to replace the orginal
capacitor?

Thanks in advance!
--
E-elephant

2008\08\26@001536 by Richard Prosser

picon face
E-elephant,
My initial thought would be NO.

For operation in this type of circuit , the capacitor normally needs
to be at least X1 rated. The alternative you're suggesting does not
appear to have this type of rating. Unfortunately most caps with the
rating and the capacitance value you need for 9mA will be physically
large.

Basically, the rating relates to the failure mode and construction of
the capacitor and is based on safety requirements if the capacitor
fails. In your specific application you may not have this requirement,
but in general, it would not pass safety inspection.

I'm also not too sure about your circuit. You appear to have a
resistor R1 in parallel with C1, while it is more normal to have a
resistor in series. It can also be useful to have a capacitor in
parallel with VD1 to act as a capacitive voltage divider and reduce
the effect of mains transients.

RP

2008/8/26 Electronic Elephant <spam_OUTelectronic.elephant.groupTakeThisOuTspamgmail.com>:> {Quote hidden}

>

2008\08\26@013314 by electronic elephant n/a

picon face
Thank you for your kindly help, Richard.

1.
I have little knowleage about Safety Standard, and I don't know what
type of products should pass this standard.
And what's this standard mean? Is it UL? Or anything else?
Emm, if this don't need to pass the safety inspection, can this CAP work?
2.
Now we are using capacitor-divider method to generate 9.1VDC, 9mA
current, and this is the most volume-reduce way as I think.
But this CAP C1 is still to big to sute our box, so I search for a
alternative CAP or another Power supply case.
Since this CAP is not safety, is there another one can replace it?
Or is there a case can achieve the requirement and smaller in volume?
3.
Thank you for your instruction of the parallel R1, thanks again.

Regards, EElephant


On Tue, Aug 26, 2008 at 12:15 PM, Richard Prosser <.....rhprosserKILLspamspam@spam@gmail.com> wrote:
{Quote hidden}

>> -

2008\08\26@014656 by Jinx

face picon face
> Now my case using the capacitor-divider to generate a 9mA current
> for payload
>
> This circuit can work fine, but the C1(0.47uF,630V) is too big to us

If it helps, 0.47uF is bigger than necessary. As 1uF passes about 69mA
at 50Hz, 0.15uF would be more like it. 0.47uF would pass 31mA

I = 6fCV

I = 6 * 50 * 0.15 * 10-6 * 220 = 9.9mA

Capacitor should be, and will be marked, X2

2008\08\26@034728 by cdb

flavicon
face


::i 'm also not too sure about your circuit. You appear to have a
:: resistor R1 in parallel with C1, while it is more normal to have a
:: resistor in series. It can also be useful to have a capacitor in
:: parallel with VD1 to act as a capacitive voltage divider and reduce
:: the effect of mains transients

I wonder if that resistor across the capacitor was aimed at being a
bleeder resistor?

Colin
--
cdb, .....colinKILLspamspam.....btech-online.co.uk on 26/08/2008

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2008\08\26@040638 by Richard Prosser

picon face
Yeah, could well be. There's no value shown on the circuit diagram but
it makes sense. Wonder what the voltage rating on it is?

RP

2008/8/26 cdb <EraseMEcolinspam_OUTspamTakeThisOuTbtech-online.co.uk>:
{Quote hidden}

> -

2008\08\26@234127 by electronic elephant n/a

picon face
Thanks, Jinx.
It's really help me a lot. :-)

On Tue, Aug 26, 2008 at 1:45 PM, Jinx <@spam@joecolquittKILLspamspamclear.net.nz> wrote:
{Quote hidden}

> -

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