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



That schematic isn't even for a flyback supply.  It's a half bridge driver,
driven by a hi/low side bootstrapping driver.  For a simple flyback you will
need some kind of simple low side gate drive IC.  The IXDD414 is one option,
but it's overkill (also it's obsolete and very hard to find, unless you go
for the newer versions).  The requirements of the gate driver will depend on
the FET you're driving and the rise/fall times you want.

-Mike

On Thu, Oct 6, 2011 at 10:26 PM, Scott Bogard <sdbogard@xxxxxxxxx> wrote:

> 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<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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