MOSFET driving with transformer

[luka]

Hi

That is for power fransformer, but I don't see why coz I don't have any problems with it, even if that is toroid

[switchmodepower]

Can you give some more details such as power levels, input voltage, output voltage, and part numbers of components.

Minimizing leakage inductance in the drive xfmr is important. A drive capacitor as mentioned is important and also how is the layout? Were those drive signals taken at just bias or a 10kw load?

Can you try to put a local pull down transistor right on the FET? If you have a long drive run this will eliminate the discharge path.

[Nejc_car]

Hi,

I whan't it to be 600W for now (hopefuly more). I tested it at 30V input, but like i said, the lower fets start to heat up).

This is how the pcb for gate drive looks. The bufer on the primary side of the trafo is on the protoboard.
http://i206.photobucket.com/albums/b...ennyB1/PCB.jpg

The signals are on gates of two fets.

Nejc

[Danko]

Today I had time to experiment with my SMPS. I tried to load both the secondary and the primary winding with a resistor, but there was no improvement on the Gate signal.

I'm going to rewind the gate-driver transformer, maybe I can achieve lower leakage inductance.

Thanks for all Your advices!

[switchmodepower]

Wind them tri-filar.

[Danko]

Yes, that'g going to be the way.

[darw82]

In order to get "perfect" waveform, you need gate driver IC, such as MC34152.

I do this on my 750W half bridge AC/DC converter with Fsw 100khz, so the SG3524 osc 200khz.

The GDT is EE14, comes from ATX PSU, I heat the core to 400C with hot air solder for 2 minute, then GENTLY (it easy to crack) pull it out from the bobbin. Wound the secondary high side first (30T), the primary (30T), and the last low side secondary, in opposite direction (30T). All use 0.16mm(diameter) wire

You may want to read slup169.pdf from TI. There is alot of example about driving mosfet.

Anyway, anybody know how to do feedback with optocoupler?

[switchmodepower]

Originally posted by darw82
Anyway, anybody know how to do feedback with optocoupler?

Use a TL431 or even a zener with an opto
See figure 1 www.venable.biz/tp-17.pdf

And also figure 3 and 4 http://www.powerint.com/PDFFiles/tec...iic_011399.pdf

[medogrizli]

What about this design for driving mosfet:

SG would drive this pair of N and P channel mosfet

would it work?

[luka]

Hi

Yes sure. But why stop there, those p-n transistors would drive trafo and you would get insulated gate drive.