Hello,

I am doing an offline, isolated, flyback with:-

Vout = 36V
Vin = 85-265VAC
Primary Side DC Bus Electrolytic Capacitor = 68uF , 400V
(Panasonic EEUEE2G680)
Switching frequency = 58100KHz


DC Bus cap datasheet:
http://www.panasonic.com/industrial/...A0000CE113.pdf


This cap has a 515mA ripple current rating at 120Hz …..and
-a 1470mA ripple current rating at 100KHz


From simulation, I know that the ripple current in this capacitor due to the 100Hz replenishment from the full-wave-bridge is 465mA.
(at maximum load and minimum Vin)

-this is just on the safe side of the 515mA ripple current rating of this capacitor at this low frequency.

…the thing is, the ripple current from the 58.1KHz switching stage is 429mA (AC RMS)


The thing is , how do I know whether or not I am violating the capacitors overall ripple current rating?

….as you can tell, at the high and low frequencies, I am within this capacitor’s ripple current rating, but surely, overall, I am above this capacitor’s ripple current rating?

The simulator gives the total overall ripple current in this primary DC Bus capacitor as 623mA (AC RMS)………

-So do you know whether or not I am subjecting this capacitor to too high ripple current?

The actual ripple current in this capacitor is obviously spread over a large spectrum of frequencies and the harmonic frequencies (from 100Hz to a few 100’s of KHz), and each individual current frequency will have a different dissipation factor……. In the face of such complexity, how can I calculate whether or not I am within this capacitor’s ripple current rating?