Re: GDT

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jan Wagner <jwagner@xxxxxxxxx>

Hi,

On Mon, 9 May 2005, Tesla list wrote:
> Original poster: "Alexander Turkin" <alex_3@xxxxxxx>
> I've got a ferrite (for a Gate Drive Transformer) but it's quite small. So 
> I have to use a thin wire. My question is: what wire can I use in it? I 
> mean how thin it can be? What currents are present there?

Any enameled copper wire ("motor wire"), if plastic insulated wire doesn't 
fit. For example 0.2mm diameter should still be ok, unless the load 
(mosfet/igbt gate capacitance) is large or/and the drive frequency is "high".

> Can I make the number of turns less (for example, 10 turns primary and 10 
> turns each secondary)? What will change?

For one, the primary inductance will drop, which then increases the current 
draw.

Secondly, if you keep the applied input voltage the same but reduce the 
number of turns, the peak to peak flux density in the core will increase 
(Faraday's Law), and there's the risk that the flux density exceeds the 
maximum the core (of that size and ferrite material mixture) can handle, 
and the core saturates. If that's the case then the GDT won't work.

If you don't like maths or designing you can still try the modified GDT 
out, though, see if it works. Just keep a finger near the GDT driver chip 
and be ready to quickly switch off the 12V power supply if the chip 
overheats real fast. And don't use any >40V voltage supplies at that stage 
of "hands on" testing!! (especially if the state of GDT pri<->sec
proper insulation is a bit, errm, unsure...)

regards,
 - Jan

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