Re: "Flyback" Driver - Why are my MOSFETS hot? (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 5 Jul 2004 20:00:07 +0200
From: gtyler <gtyler@xxxxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: "Flyback" Driver - Why are my MOSFETS hot? (fwd)

ok, looking at your waveforms I see some parasitic oscillations as
well.you may need to increase the drive resistor value, maybe 68R for
each fet. Another thing to look at is the gate voltage in the "off"
state. A totem pole does not pull down to 0v, maybe a resistor from gate
to source? The thing I don't understand is that I use totem pole drive a
lot and don't have a problem with it pulling down, the 0.7V low level
drive is usually enough, so just corrent the turn on voltage and the
parasitic problem first and try again.

----- Original Message -----
From: "High Voltage list" <hvlist@xxxxxxxxxx>
To: <hvlist@xxxxxxxxxx>
Sent: Monday, July 05, 2004 4:19 PM
Subject: Re: "Flyback" Driver - Why are my MOSFETS hot? (fwd)


> Original poster: Steven Roys <sroys@xxxxxxxx>
>
>
>
> ---------- Forwarded message ----------
> Date: Mon, 05 Jul 2004 07:35:46 +0930
> From: Matthew Smith <matt@xxxxxxxxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: Re: "Flyback" Driver - Why are my MOSFETS hot? (fwd)
>
> George Tyler wrote:
> > Are you driving the gates of the fets with 5V? If you are that is
too
> > low, you will not turn them fully on and they will get hot. There
could
> > be other factors as well.
>
> Matthew replies:
>
> Guilty as charged!  I'll put some extra "juice" onto the gate-drive
totem-pole
> and report back.
>
> Spot the guy who's spent too long working with logic levels ;-)
>
> Cheers
>
> M
>
> --
> Matthew Smith
> Kadina Business Consultancy
> South Australia
>
>
>