Re: Organic Aluminum Polymer capacitors in series for higher voltage?
- From: panteltje@xxxxxxxxx
- Date: Wed, 25 Jun 2008 06:04:38 -0700 (PDT)
On 25 jun, 09:46, "Paul E. Schoen" <pst...@xxxxxxxxx> wrote:
I need a low ESR high ripple current capacitor for the output of a
switching DC-DC boost converter, and I am considering using several organic
aluminum polymer capacitors in series. What I need is at least about 50 uF
at 60 VDC or more, with ripple current at 100 kHz of about 3 amps RMS. The
closest I could find in standard type low ESR capacitors was a Nichicon UPW
series 470 uF 63 VDC with 55 mOhm ESR and 2090 mA in a 12.5 x 31.5 mm
radial package, which is about the largest I can fit. I can get a 270 uF LF
series polymer cap in a 16 VDC rating that is good for 4800 mA, with 9 mOhm
ESR, in an 8 x 12 mm package, and I think I can fit four of them in the
space I have available.
My concern is that the applied voltage may not be distributed evenly enough
among the four capacitors, and may cause an overvoltage condition on one or
more. The same charging current will be going through each, but the voltage
will depend on the actual capacitance, which can vary 20%, so I might see
12 to 18 VDC on them with 60 VDC maximum total voltage. The other concern
is during unloaded discharge, where leakage current will vary and some will
discharge faster than others. However, if leakage increases with applied
voltage, and does not vary too greatly, it may be self-correcting, as those
capacitors with more voltage will bleed off faster than others. I would
rather not add bleeder resistors across each one to equalize the voltage,
if possible.
In theory you could use zeners in parallel with those caps.
As long as the zener voltage is lower then the Vmax of the cap, and
the sum
of the zener voltages higher then the total voltage....
Have not tried, maybe it would go poof.
.
- References:
- Organic Aluminum Polymer capacitors in series for higher voltage?
- From: Paul E. Schoen
- Organic Aluminum Polymer capacitors in series for higher voltage?
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