How to spec a power supply for capacitor charging given the simulation and large requirements?

Question

I am using the LT3751 as a capacitor charger for a large capacitor (30mF) and am trying to get an idea of the kind of power supply I would require in order to come close to the simulation charge time. However looking at the current flowing through the flyback transformer its a kind of a sawtooth with a peak of about 160A spike in the beginning of the charge cycle and then attenuates to peaks of about 40A for the rest of the charging cycle. This works out to be an average current of 7.5A. Do I need to spec a power supply for the Iavg or the peak current draw?

Power Source current (red) through Primary winding of flyback transformer:

Estimate of Iavg:

Answer 1

Irms and Vrms are used to compute Pavg with t {s} and Rth thermal resistance to estimate temperature rise.

Power Supplies are usually defined by continuous operation limits I max. Your application seems to be discontinuous. Storage caps can provide short-term current to raise Ipk slightly while other parts heat up briefly.

Ipk is used for L as the saturation levels must be avoided to prevent thermal runaway with margin. So the design method leans towards minimizing the pk/avg ratio for temporary energy storage towards 2 and your values indicate 160/7.5 implies either an oversized core or it becomes a resistor.

How to spec a power supply for capacitor charging given the simulation and large requirements?

• Consider the specs for a battery charger. CC

  • Req'd 30 mF CC 0 to 250V 5 secs Then cutoff or CV @ 250V
  • Ic=CdV/dt = 30e-3 * 250 / 5 = 1.5 A 0 to 250V in 5 s.

• Consider LED Driver CC power supply bricks

  • something like this with some defined voltage limit of 240V say at 1.5A CC