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Old 11th January 2007, 03:00 PM   #31
luka is offline luka  Slovenia
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I would say better would be "half bridge" more like push-pull, but only if you intended to have single phase boost converter.If more phases then if will be better to go with boost.And boost is easyer to go with.
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Old 11th January 2007, 03:12 PM   #32
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sorry, I forget the correct term for it. I meant push-pull.

multiphase would easily get complicated so push-pull might be the way to go.....

what about doing a boost converter but use both complementary outputs of the PWM oscillator so one inductor is storing energy while the other is powering the load. might not be a new trick but it just popped in my head.
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Old 11th January 2007, 07:13 PM   #33
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Well now,

I don't need to post a schemo. DJ nailed it! That is EXACTLY the circuit I did. A 2-Phase Boost converter. See post #8

Seriously though, I will finish it in my CAD program and post it ASAP.
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Old 12th January 2007, 03:13 AM   #34
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Default 12V to 20V 2-Phase DC-DC Boost

Luka, et.al,

Here is the schematic, FINALLY!.....

As you can see, the SG3525 drives the two MOSFETS in a 2-F topology, at 50kHz each (100kHz clock).

Inductor L1 is 24T of #18AWG wound bi-filar on a T-80-26 powdered-iron toroid colored yellow-white. L2 was lifted from an old ATX psu, and was the output inductor for the +12V section. Since the max voltage either MOSFET will ever have to stand off is 40V (2 x the 20V boost on the 2-winding coil), I thought 60V units would suffice. Switch S1 switches the output between 16v & 20V, beacuse the converter originally was for two different laptops. As this need change, and then went away all together, I decided to still leave it in, in case my needs ever changed (again!).

Last night, I loaded it down to about 6A using 3- 10W 10W resistors paralleled. IC1 stayed cool, the Q1 &Q2 barely got warm (probably because their Rds(on) is only 9mW); L1 heated up then stabilized out just like before; D2 was moderately warm, though not as warm as L1, and L2's temp did not change perceptably.

Next, I will post my single-F boost, controlled by a UC3843BN current-mode PWM chip. I have not yet built this one, and it may take a back seat as other, more important projects take precedence.

Ask me any question you may have, PLEASE!
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Old 12th January 2007, 03:15 AM   #35
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Default 1-Phase

Here's the 1-F. Clocked it about 100kHz, too, I think..........
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Old 12th January 2007, 05:50 AM   #36
luka is offline luka  Slovenia
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Hi Steve

Coil is winded like in half bridge, and connected too?

Current must add(in core), right?
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Old 12th January 2007, 08:22 AM   #37
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hey steve,

answers to your questions,
1- it is push - pull
2- isolated
3- sure, you can use at car for powering alaptop
4- you must make this transformer your selves
5- you can use a core from one of the PC PS Ei series

is it ok?
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Old 12th January 2007, 03:15 PM   #38
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hmmm.SG3525 is available here but costs around 2.5X a TL494. I'll try to adapt the circuit to use TL494.
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Old 12th January 2007, 03:43 PM   #39
luka is offline luka  Slovenia
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For that price I would to.
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Old 12th January 2007, 09:18 PM   #40
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Luka,

Actually, it is wound like the primary of a center-tap push-pull, but with no secondary. Instead, the boosted voltage is tapped at the sources of the MOSFETs, and fed to the common-anode diode. So the center-tap goes to +12V and each end is connected to its respective source MOSFET pin. Since both windings never conduct at the same time, additivity or subtractivity really doesn't matter. Think of it as 2 separate boost converters, but with their inductors wound on the same core because each converter's waveform is synchronized 180 degrees out-of-phase with the other. Clear now?

Adnancoskun,

Answers:

1) Yes and No. Yes, it is wound like a push-pull, but, No, it does not operate like a push-pull forward. It is an "interleaved" flyback (Energy is stored, then released, not transferred as in a forward converter). I guess you could call it a "push-pull flyback". :bs:

2) No, this topology is not isolated. If isolation is necessary, just wind a complete transformer with primary(ies) and secondary(ies), but use ferrite, NOT powdered iron.

3) Yes, powering a laptop was the intention all along. I just wanted to be the first kid on my block to say "I have a 2-F interleaved flyback laptop power supply"!

4)Yes, you must wind it, but that's OK. This one only took me a few minutes.

5) I DID use a core from a pc supply. The T-80-26 core came from a rather weak-kneed AT supply (only 145W, but still a half-bridge & not a flyback), and not like the current ones that have a T-106-26 toroid core in them.

DJ,

If you do the TL494 (and this would work perfectly fine), I would do the NPN-PNP buffer like what it appeard gev did for his DC-DC boost converter.
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