On Mon, Jun 11, 2012 at 5:33 PM, Veronica Merryfield <
veronica.merryfield@gmail.com> wrote:

> Hi all
>
> Has anyone worked on a system using PWM to create a SMPSU where the
> PIC/MCU supply is being generated from the PWM. I know this will need a
> bootstrap mechanism and I guess that is what I am most interested.
>
> Such systems typically have a 'start up' oscillator with values chosen
such that it gets the MCU voltage
high enough that the PIC can then take over control. Something as simple as
a 555C timer and a couple
of diodes to handle 555 reset and gate drive ORing has worked for me in the
past.
The PIC comes out of reset with most pins floating, so it can be running
for a while before it 'takes over'
the PWM cct. by enabling it's outputs.

Robert
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