Olin Lathrop wrote:

>> Driving the top transistors off the collectors of the bottom drivers
>> (which I also found attractive as it simplified the high side drive
>> requirement) produced oscillation in this application when I tried it.
> 
> Hmm.  I hadn't actually built the circuit, but I am surprised about
> that. Any idea what happened?

I'm not sure, but don't you have something like a feedback path in
connecting the high side driver /in/puts (R3, R4) to the low side driver
/out/puts (C of Q4, Q3)? Maybe the motor in the middle of it creates enough
of a phase shift for that to oscillate.

Gerhard
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