Simple half-bridge switcher 25VDC-75VAC 20kHz+ 90 to 500+ watts

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The version with 3 caps, two on the supply and one in series with the tap, is less sensitive to voltage variations on the supply. (if you run with 50% duty cycle PWM). The single capacitor solution can lead to stair case satu ration of the transformer, since the transient response steady state takes many cycles to complete and the transformer may be saturated before it sett les

Cheers

Klaus

Assuming the resistor is noninductive, which it isn't -- they're usually dropping off in the low MHz, which would lop off a few harmonics worth of power, might be enough to account for it.

If you have a current transformer or probe, you can set the scope to multiply volts and amps, and measure the average of the math signal. Beware of delay or phase shift on the probes though: not so big a deal for a resistor, but very important around reactive loads (e.g., measuring the real power in a resonant tank, where the phase shift is already very nearly 90 degrees; an extra degree and it can read negative!).

Umm... FWB and *inductor* and capacitor... right?

If the wire fits, you're already okay: it doesn't appear to be saturating, so you can run this frequency and voltage all day long (on however many turns are on there). You just need enough wire to handle the current without melting.

You certainly don't want to put a cap-input doubler on there, but there is such a thing as a choke-input doubler. You need four diodes, two chokes and two caps. You already lose half Vpp in rectification (half wave rect. each side, one positive, one negative), so it doesn't get you anything over a FWB.

Alternately, you can put the choke on the primary side, but this is more difficult to arrange on a half bridge. Full bridge (current sourced inverter) and PP (ala Royer oscillator) are in semi-common use. But then you need an extra front end chopper to generate the constant current.

Beware also, as turns go up, so does parasitic capacitance, and thus turn-on transients (primary current spikes, secondary voltage spikes). This can be improved with winding design (optimal sectioning), and addressed with snubbers (but not really fixed).

N27 is a lowish frequency material, so just keep the Bmax lower than for N87. I would think in that size, 0.2T would be fine for N87, maybe 0.1T for N27, should run plenty cool. Notice BTW that means doubling the number of turns.

This is the most common, and the most effective.

Actually that's a lie. For a decade or two, the three-cap layout dominated AT and ATX power supplies. And by quantity, that's up there in the millions. But the reason is, the filter caps were already split because of voltage doubling (the 120/240V switch wires the circuit for full wave doubling at 120, or regular FWB at 240); for the purposes of the circuit, it's a +/-160V supply, so they only needed a 1uF (typically) to "ground" (the center tap between them).

But when the supply isn't already split, you generally want to split it with equal capacitance above and below.

Ah, 935Cs, good stuff, no problems there. Do mind the stray inductance: they're simply long, so there's nothing you can do about the first

I don't know if that particular Tim reads this newsgroup, but if he did I'm sure he'd appreciate it. ;)

Umm... this:

We're no John Smith, but it's still a pretty common name. Not sure if there's any correlation to electronics, but it seems to me I've already met a Jim Williams (service engineer, retired), not the more famous (and recently passed) one; a few other Tims (not to mention the other Tim W. here), and a few other Williamses.

OTOH, Paul is a pretty common name, but I would guess there aren't many Schoens outside Europe. :)

Tim

You must be using the Larkin method of computing efficiency ?>:-}

...Jim Thompson

Once an asshole, always an asshole. Or, as you age, even worse.

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It very well could be reactive at 20kHz, so the V*A would be more than the actual power. I just measured it to be 114.9 uH at 10kHz, or about 15 ohms reactive at 20kHz. That makes it about 52 ohms impedance. Thus the output is about 88.3 watts but that is still 100.6% efficiency. The simulation shows about 90%. From the heat I detect I would estimate about 5 watts of losses or about 94%. The best measure of efficiency will be when I add a rectifier bridge, capacitor, and inductor. I may need to use SiC Shottky diodes like these:

I don't have such a probe and my scope does not have those math functions.

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Yup. Something like this:

purchased

saturating,

I think the advantage of a FWCT is two versus four diodes, which makes a big difference with expensive SiC devices, and it has less forward drop losses, but I think it requires higher voltage devices for the same DC output. However, transients can also produce higher voltage with a FWB, as shown

here:

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current.

That's too much for this design. I'm looking for something inexpensive and reasonably efficient. 90-95% would be fine.

I'll see if it saturates at 48 VDC. I could easily go to 30 or 40 kHz. This transformer was mostly a proof of concept and some practice in winding. The primary has four conductors in parallel. The entire tranny was salvaged from a trashed computer PSU.

the

I'll have to try simulations with two 20 uF capacitors in series or in parallel and see what works better. The criteria is the current through each capacitor.

inductance:

These are only similar. The actual devices are ASC USS5, which are special order surplus:

I made an offer of $1.25 each for 50 pieces and it was accepted. They seem to be really awesome: C: 20.315 uF D: 0.0008 Z: 0.785 ohms at 10 kHz L: -12.49 uH

Oops! I thought you mentioned a book you wrote? Oh, well, hopefully it will be good reading. :)

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When I was a kid the only Schoens in the phone book were my father, uncle, and grandparents. When I entered Johns Hopkins, there was a young woman in their directory who was a Schoen, but she was Jewish and from the DC area. I dated her but it didn't go anywhere. Later, as I was in line at the JHU bookstore, I watched the fellow in front of me sign his name on a check:

Paul E. Schoen! I was so floored that I just watched him walk off and I never met him. But I did Google him and he was/is an engineer working on

carbon nanotubes and such.

Paul E. Schoen US Naval Research Laboratory Publications: 66 | Citations: 256 Fields: Polymer Materials, Nuclear Magnetic Resonance, Polymer Chemistry View FAQ about top research areas and Fields of study

Collaborated with 163 co-authors from 1976 to 2006 | Cited by 751 authors

I actually called and talked to him some time ago. He said he knew of other Paul Schoens as well, and said one of them was a poet. Actually, that would be yours truly:

Whew! Long post :0

Paul

That seems awfully high, I guess that's series equivalent? I bet the measurement changes with frequency. I would guess an average 50 ohm 100W tubular resistor to be in the range of 5-10uH by construction. It isn't wound with copper, is it? (Or... perhaps constantan?)

Yeah, downside is you need $20 of them. They also have higher voltage drop on account of the high internal resistance. It might be the difference between needing a heatsink (or needing a bigger one), which could be worthwhile in the end. But I would recommend this more if it were at, say, 200kHz rather than 20, where the switching and recovery losses will be problems. Down here anything will do (e.g., UF5407?).

Well, you'll have to *rectify* that situation then, huh!?

..Which is what you're planning on..

But really, a current probe is easy: if you have some usefully sized ferrite toroids (say FT87-W or better), put down a hundred turns and hook it to a 1 ohm resistor. Bam, 100:1 current probe: 0.01 trans-ohms (100A load = 1V measured). It'll be good out to a few megs, where you get squigglies from resonant modes.

Only downside is it's not clamp-on, but that's what soldering irons are for.

Speaking of capacitance, might not hurt to have that inductor sectioned as well -- I wound this for a class D tube amplifier:

Offhand, I'm guessing if you go for off-the-shelf parts, you'll have a hard time finding a single 10mH ~2A choke, in which case that takes care of itself -- put a bunch in series and you're fine by default.

At this voltage and impedance, I'd be concerned that making a bigger winding would lead to even higher voltage spikes. You get less coupling (there's more winding to interleave, and both halves should be interleaved with each other, and with the primary!), and you waste slightly more copper (since each half of the secondary is used 1/2 the time, the RMS is

FWCT was of course massively popular back in the day, but tube rects were expensive. Like, a few bucks. Which says something about how cheap transformers were to wind. (Imagine if we could purchase transformer variants for less than the cost of diodes! Well, if you're trying to avoid the schottky FWB, I suppose that would still be true, eh?)

Tim