Other Parts Discussed in Thread: UCC28730, UCC24610, CSD18534Q5A, UCC24612
Hi,
We have modified the EVM to create a 12V/4W AC/DC power supply. (see excell file)
For the Vs measure we have: 127k (R2) / 59k (R3)
For the Vcs measure we have Rcs = 3.3Ohms (R9/R11/R12), Rlc = 4.7k
the transformer is a 750841034 from wurth (1.1mH 6:1:1)
It is working fine with 2x10µF bulk capaticitance (see VS and Vcs below under 50Ohm load):
Vs
but the current measure is already high than recommendations (but ower than the 1.5V limit).
Why is it that the lower the bulk capacitance is, the higher the current pic is? There is nothing about that in the datasheet. The spreadsheet gives a required 2µF of bulk capacitance, the datasheet advise 2µF per watt, but you cannot get the current below the 1.5V threshold unless you have more than 20µF of bulk capaticance (whatever the Rcs resistor is, for example, with these parameters, Vcs=3V under no load or load condition, so there is 3 pics and the device resets). There is almost no drop on Vbulk (1V/380V)
many thanks for your advices!SLUC579_UCC28730 Design Calculator 12V.xlsx