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Old 28th January 2013, 10:17 PM   #181
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Quote:
Originally Posted by hilli_billi View Post
Hi Nigel,
to get a 2chamber bobbin I use a 'Kabelbinder' (cable tie?).
I'm just copying an chinese LLC converter, where they did it like that. Get a 4mm gap between pri and sec. Unfortunately the design uses a l6599, which is not esy to get for hobbyist (correct my spelling ;-) )
Greetings from Germany.
Thanks for the tip.
I have loads of cable ties lying around.
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Old 28th January 2013, 11:13 PM   #182
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Quote:
Originally Posted by hilli_billi View Post
Hi Nigel, Unfortunately the design uses a l6599, which is not esy to get for hobbyist (correct my spelling ;-) )
Greetings from Germany.
Try RS Components | Electronic and Electrical Components they do them.
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Old 29th January 2013, 08:15 AM   #183
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Default L6599

Thanks Nigel, for that link. They offer it for 3.25 pounds. The german RS offers it for 6,99€.[price checked], that's rediculous. At Mouser I bought the newer, improved A-Version for 1,55 €, but 20€ transport. Only bought five, killed one. Should have orderd more, but at that time I didn't know wether the circuit would work. Since yesterday evening the regulation, burst mode, etc. is working.This evening I'll draw power.
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Old 29th January 2013, 10:39 AM   #184
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Quote:
Originally Posted by hilli_billi View Post
Thanks Nigel, for that link. They offer it for 3.25 pounds. The german RS offers it for 6,99€.[price checked], that's rediculous. At Mouser I bought the newer, improved A-Version for 1,55 €, but 20€ transport. Only bought five, killed one. Should have orderd more, but at that time I didn't know wether the circuit would work. Since yesterday evening the regulation, burst mode, etc. is working.This evening I'll draw power.
Try Fairchld ones. They are not pin-to-pin compatible, but have about the same specs (bootstrapped low and high side FET driver, soft start, and burst mode features). They also lot cheaper (at least at Farnell).
Also look at TME, they have the IRS27951 very cheap (half of the Farnell price).

The burst mode is only needed if you have totally no laod at idle. If you power an amp with this supply you will have some watts load, so you won't need burst mode.
Also at burst mode the ZVS operation fails (hard-switching occurs) for the first dozen cycles. In my experiments with UCC25600 due to the loss of ZVS at burst mode, the primary FETs dissipated more, than without burst mode!
(the burst mode only lowered the total idle power consumption by 30%)
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Old 2nd February 2013, 10:33 PM   #185
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I built up another pcb.
Fried the first 27952 but the second worked ok.

I built up another transformer a lot neater than the previous one but am getting some odd measurements, I get 43uH and 600uH. This gives a k out of range.
The pcb powers up goes to 45 volts then immediately cuts out again.
I adjusted the control components for the new Fr1 but it made no difference.

Here is a picture of the transformer the two windings to the right are laid next to each other and are the secondaries. The left hand winding under the tape is the primary. The winding on top of the tape is the aux w3inding which gave out too much voltage and blew up another chip, so I just ran the next chip dropped off 340 VDC and it worked OK.
Click the image to open in full size.
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Old 3rd February 2013, 12:01 AM   #186
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I thought winding the 2 secondaries next to each other and next to the primary would give a good leakage inductance but it hasn't.

This was the problem last time (too low leakage inductance) but last time I wound the secondaries on top of the primary so I should have expected a problem.
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Old 3rd February 2013, 09:38 AM   #187
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[QUOTE=nigelwright7557;3353489
Here is a picture of the transformer the two windings to the right are laid next to each other and are the secondaries.
[/QUOTE]

1. Put the splitter in the middle of the bobbin. If you make more width to the secondaries, the leakage will decrease. If you put in the middel, the leakage inductance will increase.
2. The two secondaries must be wind together. Pick up two wires, solder each's start to the pin, then wind the two together. (otherwise the two secondaries will have different leakge)
3. Dont use thick wire. Use wire diamater <0,5mm and trand (twist) together more wires. If you would need 1mm for that current twist together 4x0,5mm wire.
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Old 3rd February 2013, 05:42 PM   #188
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I rewound the transformer with the secondaries on top of each other and now I can get 3.5 amps per secondary.

Its not enough so I will rewind the whole transformer as you say and see if things improve.
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Old 3rd February 2013, 05:54 PM   #189
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[QUOTE=nigelwright7557;3354442]I rewound the transformer with the secondaries on top of each otherQUOTE]

Not top of each other, not next to each other, but together.
The better word is bifillary. This cause the best coupling between the secondaries.
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Old 3rd February 2013, 06:50 PM   #190
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[QUOTE=lorylaci;3354460]
Quote:
Originally Posted by nigelwright7557 View Post
I rewound the transformer with the secondaries on top of each otherQUOTE]

Not top of each other, not next to each other, but together.
The better word is bifillary. This cause the best coupling between the secondaries.
I did as you suggested.
33 turns primary, 9 turns secondaries wound bifilar.
I get 415uH and 53uH.

Reading through the app note I should be getting 115uH leakage not 53uH.

I am only getting a couple of amps out before the transformer starts vibrating and the regulation dropping out.
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