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michi's TL494 fullbridge flyback driver: need specs on diodes.

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LAN_403

termination

Wed Jun 25 2008, 12:18PM

Registered Member #1559 Joined: Mon Jun 23 2008, 10:17AM
Location:
Posts: 10

Hi all,

I'm kinda new to this forum, but allready have a good question (i think).
I'm trying to find out what types of diodes I should use for Michi's fullbridge flyback driver.
The schematic says D2 and D5 should be 10A diodes at least, and the MOSFET's should be 50V 10A each, but it doesn't say anything about the other diodes.
So my question is: has anyone built this driver (with or without audio modulation) and if so, do you have the numbers of the diodes and MOSFET's used? It would really help me.

schematic:
Fullbridge

mod edit: oversized image: original here

Kind regards,
Thom.

EDIT: found my good old friend, the IRF740. specs: 10A/ 400V/ 0.550 Ohm/ N-Channel Power MOSFET is that a good one?

Steve Conner

Wed Jun 25 2008, 12:40PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I designed the original circuit this is based on.

Those MOSFETs will work fine, but since the supply voltage of this circuit is limited to about 30-50V by other factors, their 400V rating is wasted. You could use lower voltage FETs and get more efficient operation due to their lower Rds(on).

The diodes that aren't high current could be UF4002 or whatever. The high current ones need to be fast recovery, and the same current rating as your MOSFETs.

termination

Wed Jun 25 2008, 12:59PM

Registered Member #1559 Joined: Mon Jun 23 2008, 10:17AM
Location:
Posts: 10

Hmm i see.
Something like a BUZ10 (N-CHANNEL 50V - 0.06 OHM - 23A TO-220 STRIPFET POWER MOSFET) would be better than.
Do the diodes need to be shottky diodes? (don't know the real difference between shottky and normal, so if anyone could explain that)

EDIT: the SBM1040 shottky diode seems fine. (40V 10A, see: here )

Marko

Wed Jun 25 2008, 04:07PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Looking at this again, the schematic appears wrong. There seems to be no way for pins 9 and 10 to ever get pulled down to ground, or, I'm missing some secret part of the TL494?

Second what I I don't understand is, why go stepping the mains voltage down to 30V by a transformer only to step it up back into HV by flyback transformer.

Also, the choice of Tl494 as controller seems poor to me as it only has transistor outputs with open collectors/emitters.

For driving mosfets, especially through a GDT, I always proffered to use SG3525, GDT and a halfbridge. (No need for fullbridges at power levels flyback transformers can handle).

You should be able to get SG3525 anywhere you can get TL494. I will post you a schematic if you want.

If you can get IR2152 or similar IC, you don't even need a GDT, only few extra components. They are available in digikey.

*marko wonders about very oversize picture but ignores it

termination

Wed Jun 25 2008, 05:53PM

Registered Member #1559 Joined: Mon Jun 23 2008, 10:17AM
Location:
Posts: 10

Yeah, sorry about the picture size.
OK. I got all parts (diodes and MOSFET's worked out well)
I'm using MBR1645 diodes and BUZ11 MOSFET's.
only problem is that I can't get my hands on a TC4429.
Does anyone have a good replacement for it?
I looked at the MAX626 adn it's datasheet, but can't find any maximum ratings for current.

also a little sidenote on internet orders. I live in the Netherlands, so ordering from america or japan is a little bit too expensive.

Dr. Dark Current

Wed Jun 25 2008, 06:00PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Marko wrote ...

Looking at this again, the schematic appears wrong. There seems to be no way for pins 9 and 10 to ever get pulled down to ground, or, I'm missing some secret part of the TL494?

Yes you are

The output has some pull-down built in which is sufficient to drive a small FET. However some "chinese" versions of the chip are missing this pulldown.

termination

Thu Jun 26 2008, 09:19AM

Registered Member #1559 Joined: Mon Jun 23 2008, 10:17AM
Location:
Posts: 10

*bump*
New problem!
I can't get my hands on a TC4429.
Does anyone have a good replacement for it?
I looked at the MAX626 and it's datasheet, but can't find any maximum ratings for current.

Dr. SSTC

Sun Jul 06 2008, 07:17AM

Registered Member #1407 Joined: Fri Mar 21 2008, 07:09AM
Location:
Posts: 222

termination wrote ...

Hmm i see.
Something like a BUZ10 (N-CHANNEL 50V - 0.06 OHM - 23A TO-220 STRIPFET POWER MOSFET) would be better than.
Do the diodes need to be shottky diodes? (don't know the real difference between shottky and normal, so if anyone could explain that)

EDIT: the SBM1040 shottky diode seems fine. (40V 10A, see: here )

Schotty diodes have a much lower voltage drop and a higher
effiency

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