Capacitor calculation in push pull power supply

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newtonisback

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Hello there,

I am designing push pull power supply with one input(20-366 VDC) to multiple (4) outputs.
1. 24V DC (35mA)
2. 5V(35 mA)
3. 13V(35 mA)
4. -13V(35 mA)

I used full wave rectifier. Now problem is....How to calculate values of filter capacitors for rectifier side and all output side.

I found that ripple current is depends on cap.

Is there any specific calculation for calculating perfect calculation for the capacitance.?

Please help me solve this.
 

The RC time constant is one avenue to try.

Example... given these specs:

* you permit 3% ripple.
* load is 40 ohms.
* smoothing capacitor is replenished every 1/1000 second.

The time constant (TC) is R * C. Defined as the time for output level to drop 63%.

You permit 3% drop in 1/1000 second. This translates to 63% drop in .021 sec.

TC = R * C.
Or, C = TC / R.

.021 / 40 = 525 uF. Value for smoothing capacitor.

There is another formula, based on amperes going in and out of the capacitor, per cycle.
 

    V

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Right, a rectified square wave becomes DC, more or less. There will be less need for a smoothing capacitor.

I was only guessing at what waveform he will have. Say, the ordinary pulsed or triangle waveform, where the capacitor powers the load during idle gaps.
 

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