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UCC3809-1: Flyback converter : Input capacitor ripple current calculation

vaibhav waman
Intellectual 320 points
Part Number: UCC3809-1

Tool/software:

Dear Team,

Currently I am designing flyback converter. There while selecting input electrolyte capacitor do I need take care about ripple current at input side ? if yes what is the best way to calculate this input current ? any formula, application note will be helpful.

BR,

Vaibhav 

  • 0
    TI__Guru 73715 points

    Hi,

    For a dc input voltage source, first estimate input average current, I_in_avg, at input low line and full load duty cycle, Dmax.  Then

    The input capacitance can be estimated as C_in >= I_in_avg x Dmax / (fsw x delta_Vin)

    fsw - switching frequency

    delta_Vin, input voltage ripple, rule of thumb is < (5% x Vin) as an initial starting point.

    Aluminum electrolytic capacitor is usually ok to use paralleled with a high frequency ceramic like 0.1uF to 1uF.

    delta_Vin is affected also by the source internal impedance, connection length, layout, transformer leakages, so you would need to make bench debugging to tune up to finalize.