IVP wrote:
> Basically it's a drive system for two specialised sensors. The first
> draft of the circuit is pot controlled, manual or motorised. The
> customer has asked for a swell function, pot and/or micro
> controlled, so the output would now look like an old-time wooden
> rollercoaster with the area
> under the curve filled in with adjustable PWM

I suggested this yesterday, but some messages apparently got sucked into th=
e
black hole of the list server.

Anyway, there is no need for adjusting the high side of the PWM at all, as
long as the load only "sees" the average value.  Always use the full (35V
was it?) and take care of everything else by modulating the duty cycle
appropriately.  This includes the user control.  Ditch the LM317 linear
regulator altogether and wire the pot into a PIC A/D pin.  This becomes one
more input to the final duty cycle calculation.

> The attached shows one of the H-bridge controllers.

Now I'm even more confused.  Your previous schematic was modulating the hig=
h
side of the PWM pulses, up to a high of something like 35V.  This shows the
H bridge and the motors all running from 5V only.  Presumably the previous
PWM outputs were for driving the H bride?  They had pullup resistors and
certainly weren't suitable for driving the motor directly.  But why do you
want to modulate the high side voltage of these pulses since they always
need to just saturate the transistors?

Another problem is that there is no place for the inductive energy of the
motor to go during the off phase.  The normal catch diodes are missing.
There should be four schottky diodes, one string of two from ground to powe=
r
on each side of the H bridge.  Perhaps you can argue that the top NPN
transistors will provide the low side clamp, but you still need diodes to
the power rail.


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