Re: [TCML] Driving a flyback off of mains gate drive woes.

[Scott Bogard <sdbogard@xxxxxxxxx>]

Hi Dave,
     Yeah I saw that schematic, it kind of gave me the idea, switchable 
from 120 to 240 volt operation, super high power capacity, but there are 
limitations with that chip I'd like to circumvent.  Namely that it is 
stuck on 50% duty cycle (overall flyback duty cycle is independently 
controlled by a second oscillator at a low frequency) and that you have 
to use the built in frequency generator (I have a frequency generator, 
that I can program frequency routines into.)  Basically I need some kind 
of plane Jane MOSFET driver that I can mount to the high voltage rails 
like that chip, but that accepts an external input 5V logic, I don't 
think such a thing exists, so there must be some way to build one...  
Can I make a BJT totem (I think that is what it is called) fed by like a 
3k resistor or will that pop under that voltage?  Thanks in advance for 
your help guys, it is so much appreciated by this solid state newbie!

Scott Bogard.

On 10/6/2011 8:20 PM, David Speck wrote:
> Scott,
>
> Below is a link to a full schematic for a flyback driver off the 
> Information Unlimited website.  No personal experience to know how 
> well it works, but it seems to be a close match to the sort of thing 
> you are looking for.
>
> http://www.amazing1.com/download/PVM500BASICSCHEMATIC.pdf
>
> Dave
>
> On 10/6/2011 6:40 PM, Scott Bogard wrote:
> > Greetings all,
> >      Back up to my old tricks again.  After procuring a schematic for 
> > a PVM 400 flyback driver, and noticing it runs off of mains voltages, 
> > I am attempting to create my own version, with programmable 
> > adjustable duty cycle and frequency.  What I don't seem to know how 
> > to do, is drive the gates, what I have is an ATmega chip producing a 
> > nice 5 volt square wave, of variable duty cycle and frequency (3-300 
> > kHz) and some good flybacks.  Obviously I cannot just plug that 5 
> > volt signal into a bunch of MOSFET gates, it would likely not have 
> > the guts to hold them open, even if it was the correct ground, which 
> > it is not.  So basically what hardware is needed, a gate drive 
> > transformer?  MOSFET driver?  Could somebody please point me to some 
> > straightforward literature about biasing MOSFETS, and possibly 
> > provide part numbers, not just reference "generic BJT."  I know it 
> > must be possible, people have run solid state TCs off of MOSFETs for 
> > a long time, so what am I missing...  Thanks in advance, I'm looking 
> > specifically to run it off of about 320V DC (+-160V) low side drive 
> > (not half or full bridge) if that makes a difference.
> >
> > Scott Bogard.
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