# How can I calculate the input capacitance required for a push-pull step up converter?

How can I calculate the input capacitance required for a push-pull step up converter? Vin - 12V (dc source) Accepted Vin ripple = 100mV Duty Cycle = 50% Switching frequency = 300kHz Vout = +12V and -12V (multiple output) Iout = 0.5 A

• 1) there's no input cap in your schematic only an output cap. Add the capacitor you're talking about to avoid confusion. 2) without knowing how much ripple there can be allowed on Vin and how Vin is created, how much current flows etc. It is impossible to answer this question. – Bimpelrekkie Feb 26 '18 at 13:00
• You added some info but from that the Cin still cannot be determined. Also you need to think about where the ripple comes from. Suppose Vin is 12 V DC from an ideal voltage source, how much ripple would there be on Vin? Now if Vin is supplied by a voltage source with some series resistance now what will the ripple be? Your question is similar to asking: I have a car, it has 4 seats, weighs 1200 kg and runs on petrol. What color is my car? – Bimpelrekkie Feb 26 '18 at 14:10