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Class D Switching Power Amplifiers and Power D/A conversion

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Old 20th April 2007, 06:22 PM   #401
luka is offline luka  Slovenia
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Hi

Wow first time of-line, full bridge (is it?), 1.5kw, and my personal best that you use toroid. I would like to know everything about it. My first try was with ETD44@ 50kHz, unregulated, did put out 550w and I also plan to have PFC just for the same reason as you do, too big caps on input.

Quote:
The sum of power supply ripple and the amp ripple at voltage buses is really a mess
That might be beating between smps and amp. I didn't have any measureble ripple, just 100Hz from mains, but I didn't connect amp as load but resistors
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Old 20th April 2007, 07:02 PM   #402
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No, itīs really half-bridge, 2 irfp in parallel at each side.

I have some knowledge on smps design (push-pull battery powered) so that the things ran more easily than I supposed for first time.

Itīs a little "hard" for a half-bridge design, I know, but it will not be used at continuos levels. Iīm really curios if it will reach this level of power.

I like toroidals. Another PITA was winding it using triple insulation. But itīs working well.

I tested it at 500w continuous at output during one hour. No problems at all.

BTW, the gate driver and current sensor are toroidals too.

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Old 20th April 2007, 07:10 PM   #403
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Hi

What toroid do you use? Do you have it regulated? And do you have current limit? How can you test it at that much power over that long period of time?

Hope to see some pic someday
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Old 20th April 2007, 07:39 PM   #404
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I used a 62mm toroidal core and there is current limiting (functional but not enabled yet - I will enable it after full power tests).

Since it is a 140VDC design, I put a bunch of 220v/200w bulbs in order to drain more or less 3A from the power supply. Used sunglasses to adjust this gadget....

It is an earlier photo of the prototype. I used a large pcb mounting because I planned to fit it exactly in the chassis and, as a first design, I was very conservative on building it.

Best regards,
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Old 20th April 2007, 07:45 PM   #405
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this is the toroidal before placement on the pcb.
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Old 20th April 2007, 07:46 PM   #406
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Hi

This is all in 1HE casing, right? I could say what happened to trafo, but I hope you will tell me what you did, some kind of insulation, or maybe that wires don't move. How did you winded it, how many turns/wires used? What is DC voltage on output, can you set it? I'm asking this because I'm not sure if you use your amp with 70v or you use it with lower value now. And one more thing is that +/-70V or just 70v(like +/-35v)

If I can just say, if you did use coupled output inductor, it would be much better if you would use toroid for that too.
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Old 20th April 2007, 08:23 PM   #407
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I did it a year ago, but let me see if I remember right:

This is all in 1HE casing, and I have an EE core that fits ok for it too. But I like toroidals.

The insulation was done using poliester tape for transformers and a red high voltage 3m tape. the primary first and the secondaries after that in a bifilar wound. Not the best considering coupling but easier to wind. the end of the wires were isolated using thermal material. And everithing was glued using high voltage silicon adhesive. Itīs solid rock mounting and after lots of tests appears to be OK.

The wires are 18awg in parallel. I used the formulae of McLymanīs book (excellent books from this author). I donīt remember the values, but itīs easy to retrieve, if necessary. They are in some notepad here, elsewhere.

Iīm using a linear regulated power supply for 35vdc tests and this smps for 70vdc tests, both symmetrical.

And, yes, the toroidal core for the output coupled inductor would be much better, but I donīt have them available easily here in my country for iron powder or other similar material. Just ferrite ones. It is a coupled inductor using pot-core gapped ferrite.

The number 2 toroidal output inductor core I bought a year ago when travelling abroad. But even for it I will use a gapped pot-core after final adjusts of the amp.

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Old 20th April 2007, 08:33 PM   #408
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Hi

If it is not too much trouble to find values. It would help me see/compare your test with my. We both did it at ~500w but the thing is that my is +/-35Vdc idle, but goes down to +/-22Vdc at that power. Thats why I would like to know number of turns and if possible voltage at idle and 500w so I can compare them with my.

Do you have any info for your trafo?
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Old 20th April 2007, 08:41 PM   #409
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If I remember your design is a not regulated one. Mine is full regulated. But I think this drop is excessive even for a unregulated one.

Give me your initial setup for it and I will compare with my calculations.

regards,
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Old 20th April 2007, 08:55 PM   #410
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Hi

not regulated,330Vdc on input caps, primary is 35 bifilar, two secondarys each 7 trifilar,50Khz, 2x1000uF for each rail.
I winded it like this: 1/2Pri,both sec and again 1/2Pri.
Core is ETD44
Do you need anything else?
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