I've seen a third method:
+ ------+-------+
        |       |
       A=On    B=-PWM
        |       |
        +---M---+
        |       |
       C=Off   D=PWM
        |       |
- ------+-------+

Here during the ON cycle the motor turns, and during the OFF cycle the
motor breaks (but does not try to turn backwards). This method is
equivalent to PWMing the entire right side half-H bridge, while the
previous method (1) is equivalent to PWMing the Enable signal for the
right half (with fixed driving direction signals).

I would be interested in seeing how this method compares to the other
two. On one hand, here PWM=0% really means off, and no energy is wasted.
Plus the motor breaks when speed=0, which may be desirable. On the other
hand, on PWM=50% there is probably a lot of energy wasted.


-- 
Hector Martin (hector@marcansoft.com)
Public Key: http://www.marcansoft.com/marcan.asc

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