Bob Blick wrote:
> OK, how about this one I posted long ago? Since the design you
> posted had no freewheel diodes, I assume you are not doing high
> speed PWM, so this design also has no diodes. Use jellybean parts.

I like the basic topology.  Note however that the two inputs can't be raised
all the way to the same supply driving the H bridge.  If they were, the top
transistor wouldn't come on very far, if at all for practical purposes.

The input transistor base is a the + rail.  Its emitter is one B-E drop
lower.  However it's collector also needs to be one B-E drop lower for the
top transistor to turn on.  There is at least one saturated C-E drop missing
in the top transistor drive circuit.  Chances are the top transistor will
need a little higher B-E drop due to its larger current.

The solution is easy and only costs two extra resistors.  Put the existing
resistor in series with the input transistor collector, not emitter.  Then
add a base resistor for the input transistor.


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