How to calculate dQ?The voltage increase from this constituent is V2 = dQ/C
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Is it an offline or DC-DC Power supply?Hi Team,
I have requirement for power supply output
1. Output ripple 100mV
2. Hold up time>1 Seconds.
I have switching frequency of 40KHZ-100KHZ
How to calculate capacitor value
Regards,
Marx
what is I?dQ is i dt
it is flyback topology.Is it an offline or DC-DC Power supply?
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Oh! You meant for the output? What topology is it and why output and not input?
Sure, holdup time requirement is for output holdup. Depending on topology and on configuration (i.e. whether step up or step down), it can be implemented either with the output capacitor or the bulk capacitor.it is flyback topology.
Hold up time requirement is applicable for output, so we want to have Hold up time for output only.
what is I?
is it Load current? ripple current?
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I is the load current
@Easy peasy
you estimated a hold up capacitor on the input side
did you include the power to operate the converter, or just the load power?
considering you calculated a 2000 uF capacitor, its easy to use a bigger
cap to incorporate the efficiency
@Bjtpower
whatever scheme you use, add about 20% to the capacitor to
ensure margin for temperature variations, aging, and component variations
For sure you are right. I forgot about loss of source. Sorry.if the source is gone, then the load current and the capacitor current are the same
This is often done - all the way up to 400V on a 450V electro ( the higher volt electro stores more energy in a smaller volume )I am just wondering if you should put a secondary circuit in there..involving a big capacitor being charged up to 60V say, and then a buck on the output of it which switches in and supplies the output when it drops out....I mean this stops your Vout drooping too much.
Hi ZenerBJT,Ripple voltage on output capacitor of SMPS.
The ripple voltage is the sum of the squares of the two constituent parts.
One part is from the actual peak current magnitude which goes into the capacitor and its product with the ESR of the capacitor.
V1 = I(PK) * ESR
………………………………………………………………
Other part is the actual charge that goes into the capacitor each switching cycle (this obviously equals the charge that goes out of the capacitor each switching cycle).
The voltage increase from this constituent is V2 = dQ/C
……………………………………………………………………..
And the overall ripple voltage is….
SQRT (V1^2 + V^2)
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As an example......the calculation given works for the following attached boost converter...which is in LTspice simulation here.
Of course, you can just cheat and measure it on the LTspice sim
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And id say youd want to do the calc at your lowest switching frequency, and the maximum power.
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