IVP wrote:
>
> >> [half bridge example] would go full speed forward with 100% duty
> >> cycle, stop at 50%, and full reverse at 0%
>=20
> could you describe that configuration please ?

It's a pity that the PIClist is text-only, but anyway to visualise this,
take a look at this diagram (not mine):
http://www.jcminventures.com/Cybugs/L293sch.gif.  A similar arrangement is
illustrated in the L293 data sheet.

It shows a BDC motor connected directly across two outputs (1Y and 2Y) of a
L293.  If the 1A input is high, and 2A is low, 1A goes high, 2A goes low,
and the motor spins in one direction.  Invert each input, and the motor
reverses.

Now imagine, instead of the transistor and switch arrangement shown in that
that diagram, that the 1A and 2A inputs are connected directly to a
PIC16F684's P1A and P1B PWM outputs.  In half-bridge mode (ignoring
dead-band delay), these outputs are complementary.  Assuming active-high
outputs, with a 0% duty cycle, PA1 is off, P1B is on, and the motor spins
one way.  At 100% duty cycle, the opposite is true.  A 50% duty cycle
implies an alternating (but balanced) forward/reverse action, which may not
be good for the motor (although I suspect that at a high enough PWM
frequency it wouldn't be an issue), but mean a stopped (but still working)
motor.

That's the theory, anyway.  As I said, I've never used half-bridge PWM used
for motor control in that way, so may be just a very bad idea.  I'll try it
and see what happens...

Cheers,
David



--=20
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