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'[EE] or PIC question about SMPS'
2004\06\08@174249 by Martin Klingensmith

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Some background info:
I'm working on building a full bridge SMPS power supply. It will take
the 13.8v nominal automotive source and boost it to about 50 volts. This
is done through a high frequency transformer.
The primary is driven by a MOSFET H bridge [hence "full bridge"]
To keep the flux matched for both current directions, each directional
pulse from the H bridge must have the same on-time duration. To clarify,
if you had a 50% PWM signal coming out from a controller, you could take
the inverse and have the two signals you would need to drive the H
bridge, however; if you had a 40% PWM signal and you inverted it, the
on-times would be 40% and 60% [POP goes the MOSFET - unbalanced flux in
the transformer core].
So if anyone has any ideas on how to do this, I'd be glad to hear them.
I prefer using PICs or logic gates where possible because they are
easier to breadboard and cheap, but I will take any advice.
Thanks everyone.

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Martin Klingensmith
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2004\06\08@181637 by Peter van Hoof

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I would take the first pulse from the pwm and drive side 1 of the h bridge
and the second pulse to side two and repeat the cycle

Peter

{Original Message removed}

2004\06\08@231617 by Martin Klingensmith

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Thanks for the tip Peter. Any idea how to do this with hardware PWM from
a PIC?
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Martin K

Peter van Hoof wrote:
> I would take the first pulse from the pwm and drive side 1 of the h bridge
> and the second pulse to side two and repeat the cycle
>
> Peter
>
> {Original Message removed}

2004\06\08@235603 by Peter van Hoof

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I have not exactly worked this out but how about something like this
Dont use the actual output pin of the pwm
instead use the interrupt on change and a interrupt service routine
to toggle two output pins at the appropriate moments

Peter

{Original Message removed}

2004\06\09@053949 by Dave Dilatush

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Martin K wrote...

>Any idea how to do this with hardware PWM from
>a PIC?

Some of the newer PICs, like the PIC18F1320, have an enhanced CCP
module that can generate all the drive signals for an H-bridge.

dave D.

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