Help with PSU design - 2Kw unisolated Buck

[Vectrix150V]

Re: Help with PSU design - 2Kw unisolated Buck

Well, I was going to post some more measurements but I managed to kill the UC3842 again - sigh.

Time to buy some more.

It is (was) stable at about 300mA, with a 0.47R current sense resistor. I ended up using a very similar design to the one on the front page, but with a 15 K resistor in series with pin 2, so the gain of the error amplifier would be fixed at 10 (with the 150K from comp to VFB).

The frequency was 100Khz (15K and 10nf for Rt and Ct) with a 270uH inductor and a 200uF capacitor on the output.

I had a 10nF cap across the opto pins as well.

Very tempting to move to something like the NCP1216 - fixed frequency, pulse skipping, internal ramp compensation, 250us current sense blanking and 500mA totem pole drive, and direct optocoupler connection.

[Vectrix150V]

Re: Help with PSU design - 2Kw unisolated Buck

Whilst thinking about the lowside buck topology, I considered how on earth someone would perform output voltage monitoring in a buck PFC - I remembered the UCC29910A (that I could never lay my hands on GRRR) and had a look through the datasheet.

Lo and behold - they use a level shifter (on page 10 - of https://cdn.badcaps-static.com/pdfs/...6fea22c9c4.pdf) so I can toss the optocoupler and the TL431 that are proving to be a major PITA in my design, and monitor voltage directly. At least I can compensate normally with this design, and cull the parts count down even furthur (and not have optocoupler degradation, drift and failure to consider).

Isolation is not an issue, the output is unisolated, the opto was a cheat because I couldn't think of anything else to do the job.

Time for more parts, and a redesign of the PCB to incorporate this - fingers crossed.

[Th3_uN1Qu3]

Re: Help with PSU design - 2Kw unisolated Buck

That's a good idea. The key to any circuit is to make it as simple as possible, and avoiding an opto and TL431 when you can is a good idea. Good luck.