CCM boost inductor design

Is 1.2 mH the no load or full-load inductance? That sounds like a mammoth inductor for that spec, even if that's the no-load inductance. Check math again?

Basically, I am considering

It's at full load. Math is right and you are right as well. CCM boost inductors just *are* huge. Usually much bigger that the downstream converters they supply.

Best regards, Piotr

Maybe break it up into smaller ones in series?

Is it worth designing this? MeanWell and other power supplies are good and incredibly cheap.

They don't have 600-volt outputs. Even if you hack one for its non-isolated PFC bulk-capacitor voltage, that's only 400 volts. I've long been unhappy about the scarcity of commercial high-voltage supplies.

This game doesn't pay off. L scales up with N^2, B, H and DCR only with N. So splitting a 2L monster into L+L means higher total core losses and ohmic losses. It's better to buy a bigger core or increase the switching frequency.

Same with interleaving. The complexity is not worth the trouble unless you have no other option or there are scalability requirements.

Best regards, Piotr

DCR may scale with N, but multi-layer proximity effect losses scale more like N^2, or even stronger. Likewise core losses can scale by a squared factor. So if you can't get a big enough core, it may be better to use several as large as you can get; 500 watts is a lot for a single core.

I agree, and have recently used their medical-grade insulation PSU for about 40 bucks in one of my devices. Insane.

But this time the PSU must not contain any electrolytic capacitors and there are cooling problems. Hence the pretty unusual efficiency requirements. The 600V bus voltage is also a consequence of these requirements. The energy stored in a capacitor is proportional to the square of the voltage -- a 47uF capacitor will suffice. Such 900V foil capacitors do exist and cost about 10 dollars, which is pretty cheap if you consider the future service costs.

There already is an FPGA in the system, so using it to implement the totem-pole bridgeless PFC with synchronous rectification has the added benefit of great educational value.

Best regards, Piotr

Interesting, can you provide some pointers?

ASC will do HV Foil caps, custom to if you need quantity. Dearborn has similar foil caps.

Cheers

Absolutely correct, but the ACR losses also scale with I_AC^2, which is pretty low in a decent CCM. 5:1 I_DC-to-I_AC ratio can buy a lot of power budget to spare on the AC losses. So my working hypotesis is that only DCR (and unwaned resonances as a higher-level effect) matter in CCM. I would be happy to have this falsified by the experts inhabiting this group.

I crave an all-practical book on magnetics similar to your AoE. What are the quantitive properties of foil winding? How are AC losses impacted by orthocyclic winding as compared to helical? And so on. And tons of FEM simulations of current/flux density.

This knowledge can be found in the Internet, but is very scatterd. Mr. Legg has once sent me a lot useful materials on the behaviour of foils.

Oh, definitely. Or start interleaving.

Just E42/15 KoolMu/MSS, acceptable. Ferrites can't come even close to this size and there are no discrete gap issues. But the core losse per unit volume compared to the modern high-performance ferrites and the number of turns don't look very good. Eh, these tinky compromises...

Best regards, Piotr

On a sunny day (28 Jul 2019 09:36:47 -0700) it happened Winfield Hill wrote in :

If you do not need a high speed switcher, then for that sort of HV use an old tube transformer (2 x 240V or something) to get isolation, add some diode bridge, thyristor for control, filter choke, filter capacitor.

I make 110 V 60Hz here in the 230 V 50 Hz world using a power audio amp and an audio amp 230V mains transformer in reverse, powered by 'sgen' signal generator in Linux, slider for output voltage, Sometimes you gotta work with the things you have laying about. Select any frequency within reason, 50 Hz, to 400 Hz should work.

Now if you are smart you feed the output AC via a divider back into the audio line input, and write those famous few lines of code to adjust the mixer setting so the output voltage stays constant.

I use MKP1848C65090JY5, for example:

At 600V derating their useful life approaches ~1e6 hours.

There are even bigger units, but the price is a super-linear function of the capacity. Electrically and economically it is better to buy 2 and connect them in parallel.

Best regards, Piotr

With the full-load requirement equation there I get ~ 1 mH so hmm yes about right.

You could decrease the required full-load inductance by nearly half if you could accept a 5% higher deltaIL and run 50kHz higher

We will wait, Piotr, to see your results!

That's a very nice choice, I like it. Thanks!

KoolMu is great stuff. Other people are now making equivalents. I was burning the paint off powdered iron toroids, and CoolMu came to the rescue.

Don't you just need X pounds of core and copper for a given application? One big inductor or several small ones?

The only difference, seems to me, might be surface area/cooling, which would favor several small ones.

All the PC power supplies with boost mode PFC that I've seen, of about

See e.g. time index 13:00

The specs for this design don't seem that much different so idk why need to go to two coils. 500W isn't an absurd amount of power. The difference in efficiency between 20% current ripple spec and 25% will probably be like 98% vs 95%...is this important

If you use toroids there's no law that you can't glomp two toroids together, like stacking donuts, to get more effective core volume and winding surface area, it's done all the time