Josh Koffman wrote:
> I've attached a schematic of what I'm thinking.

The way T3 and T4 are driven will cause both to be on during transitions.
Think what would happen if the PIC output were held at 2.5V.  Bipolars
generally take longer to turn off than to turn on, so both transistors will
be on for a while after each transition.

T1 is never going to come on as you have it.  It looks like maybe you
intended T1 to be a PNP?

If you could drive T2 from a separate PIC pin, then you could lose T4 and R=
2
completely, and also guarantee break before make timing.

It looks like your intent is to have T2 on during normal operation.  That
charges C1 to 11V.  Then to do a extra brightness pulse, T2 is first turned
off then T1 turned on.  This raises the bottom of C1 to the power voltage,
with the top side twice (minus the diode and transistor drops) the power
voltage.  The energy in C1 produces the extra brightness.  C1 decays to
empty, and you start the cycle over again.

However, D1 and R1 make no sense.  It looks like R1 is meant to make the C1
charge current finite.  That's a good idea, but it's placement isn't.  Note
that D1 defeats that purpose.  As you have it now, R1 does nothing to limit
the C1 charge current.  It only gets in the way during the extra bright
pulse.

You could lose D1 and put R1 in series with the collector of T2.  That
limits the charge current, but won't get in the way during discharge.


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