I'm building a 800W power supply and so far things are going well except the inrush current peaks at around 13.5A at the secondary. Which is a lot lower than it was before I installed a choke on the filter and a soft start on the primary.But 13.5 A is still to high . Its causing the Op amps in power supply circuit to "lock up" and stop functioning until I reset the system by switching off the power then on again before the capacitors can discharge completely.I tried resistors at the op amp inputs but it changes the dynamics of the circuit to much, Voltage and current control just won't work right.
I want to modify this soft start module I have by installing more thermistors and how they are configured but I'm not sure if I'm calculating the inrush current correctly .From what I understand I can calculate the inrush current with:
R = 1.414V
ac / I
The calculation seems to concur with the 13.5A at the secondary I get now with the 10 Ohms NTC configuration the soft start has right now.Around 4.3 A at the mains primary.
So If I put (5) 10 Ohm NTC in series for a total of 50 Ohms I should be able to reduce the current down to around 3A at the secondary.That should reduce the primary inrush down to around 1A
The modification involves making some cuts in the PCB trace and drilling new holes eliminating NTC 2 and 3 and replacing 1 and 4 with NTC 10D-25 then adding the remaining 3 in new locations. I have lots of the 10D-25
https://datasheet.lcsc.com/szlcsc/NTC-Thermistor-5R_C69391.pdfAm I on the right track? And are there other considerations I should be aware of?
Like the steady state current I figure its around 6 amps .
I
ss = P
out/V
ac X 90% Efficiency
And how to calculate the energy through the NTCs to make sure they're rated high enough?I'm having trouble with that calculation.
I get crazy numbers that don't make sense.