Big. Honkin. Core.

[Th3_uN1Qu3]

I'd already tossed the CRT of the 21" iiyama monitor so i proceeded to take apart the guts. I'm telling you, this has got to be the most overbuilt SMPS transformer i have EVER seen.

The monitor was rated for 150W consumption. Well, the main transformer had more layers of insulation than it had wire, and there was still space left! And when wire was wound, it was only wound in the center, about 2/3 of the total core surface. The top and bottom were covered with plasticky tape rings, then a layer of insulation on top, and so on.

I finally got to unwinding all the tape, and found out the core is *gasp* an ETD49. I thought it'd do around 700W, maybe 1kW... well, it turns out it can do 2kW. TWO kilowatts. You have got to be kidding me. Also the core is gapped about 1mm in the center leg, which makes it perfect for a forward converter. Now... at low line conditions 2kW means a whopping 25 amps peak transistor current. Now, time to find some switching devices that will take that kind of current without burning a hole in my pocket... this is gonna be fun.

In the monitor a single switch forward configuration was used, with one of those on a rather small heatsink, this points to high efficiency. Maybe that's why such an enormous core was used. Well, better for me.

Here's a pic of the ETD49 alongside two cores common in ATX supplies, i'm sure you know them. This should give you a good idea of the size of this beast. And i haven't talked about the flyback transformer yet...

[Wizard]

Re: Big. Honkin. Core.

Actually this was designed around low frequency SMPS back then. Old SMPSes tend to have big cores.

On CTC169 by RCA, that size of core for SMPS is used on 15.7KHz sync'ed to flyback frequency. Very true. Even the vertical drive is chopped by a SCR and power source is 15.7KHz AC from flyback (isolated two pins), SCR modulates this into vertical sweep by pair of op amp 8 pin ICs one pulses into ramp, and other to convert it into PWM pulses to drive SCR.

I had for first time ever to see planar tranformers used in SMPS for UN55C8000 (Samsung high end LED LCD TV). The transformer is what unusual part is copper is not wound, rather the one green, THICK fiberglass block with winding patterns embedded into it into layers too. Ah, single PCB planar transformer. Very cool. Judging by few turns visible through the green PCB, it is based on ultra high frequency (we're talking 100KHz even more at about 130W or so).

http://www.google.ca/images?hl=en&q=...w=1042&bih=614

Cheers, Wizard

[Th3_uN1Qu3]

Re: Big. Honkin. Core.

I believe 100kHz is "low" by today's standards... The supplies i build switch at 100kHz. I agree that for low frequency use you need a bigger core... but still that's a lotta core for 150W.

[kaboom]

Re: Big. Honkin. Core.

On that Mitsubishi V18 RPTV, the transformer core looked like it was capable of an easy 800 watts. Didn't even measure the core before I put the set back together- it may have been a -49 series. Quasi-resonant flyback with an STR-F6628. A 5-lead TO-3P/247 device, but like a giant TOPswitch.


http://www.surplussales.com/Inductor...FerPotC-2.html

You don't have to depend on junked units for cores. I've ordered from them, they also have toroids, Essex wire, Teflon tubing/sleeving, fiberglass sleeving, insulation tape, etc. The pix are the -52 series core & bobbin set at the top of the linked page.


-Paul

[Th3_uN1Qu3]

Re: Big. Honkin. Core.

You don't have to depend on junked units for cores.

I've been long wanting to make an order of ferrites, but as long as i still have cores from junked ATX supplies (which i can get for under $2 a pop and sometimes they're still working), i don't see the point.

If i'll be making any real high power supplies like 2kW... then maybe i would order a bigger core.