Re: [TCML] Gate drive transformer help

[Scott Bogard <sdbogard@xxxxxxxxx>]

Hi Mike,
     What I am seeing on the scope is the wave form is hardly square, it
starts and bumps up high, then comes down; at higher frequencies this is
where it ends, but at lower frequencies it then cuts out, then comes back
up at about 3/4 height and ramps down, breaking a single pulse into two.  I
have a lot of off axis inductance, the thing was gator clipped together,
and subtracting 3 out of the 17 turns made no difference...  When I turn
down the duty cycle, the two bumps merge, and form one distorted but stable
bump, I can run really low frequencies at less than 10 percent duty
cycle...  I need a gate drive transformer because I am going to be running
this thing off of 300V DC once all is said and done (always though using a
step down transformer to drive a step up transformer was ludicrous...)  I'm
not using a resistor from the driver output to the transformer, and my dc
blocking cap is .68uf I believe...  Not even sure if it is necessary for
proper operation, tried doubling this and halving it, no appreciable
difference.  Thanks for your input guys!  Oh and my turns ratio for the
xformer is 1:1:1...

Scott Bogard.

On Mon, Oct 31, 2011 at 8:34 AM, Michael Twieg <mdt24@xxxxxxxx> wrote:

> If you're seeing "distortion" only at lower frequencies then that probably
> means you don't have enough magnetizing inductance.  Your driver may be
> drooping due to excessive magnetizing current, or the core is saturating.
> Though without a better description of the "distortion" it's hard to say.
> Just try adding a few more turns and see if it helps.
>
> -Mike
>
> On Sun, Oct 30, 2011 at 6:26 PM, Scott Bogard <sdbogard@xxxxxxxxx> wrote:
>
> > Greetings all.
> >     Built my gate drive transformer for my flyback driver, oddly enough
> > when scoping it it works great at higher frequencies (30+kHz) but
> distorts
> > below that, except at low duty cycles.  So my questions is do I need a
> > different core material, possibly a larger core, fewer turns?  I have one
> > larger core, and also several smaller ones, the larger core is already
> > wound but seems to only work at much higher frequencies in that
> > configuration.  Also tried doubling and halving the dc blocking cap,
> didn't
> > change much...  Any advice would be greatly welcomed.  Also the waveforms
> > are a bit distorted even when they are stable, up until very high
> > frequencies (100kHz ish) I still think I could use them this way but
> seems
> > to me changing parameters should fix that as well, at least my my
> intended
> > operating range of 10-100 kHz...  Thanks.
> >
> > Scott Bogard.
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