First, thanks! I totally overlooked that...That's the price I pay being a comp. eng. instead of an electrical eng...at least the code is a breeze
The current reqt.s for the biggest motor I might drive is 4A I expect the stall current to be ~10-15 (I can't measure higher than 10A, and the big motor is really powerful (difficult to stall)) Worst case I can drive this motor in one direction using a separate already proven circuit.
More importantly I have two smaller motors 3.3A stall current @12V for locomotion (i.e. definitely need H-bridge)
**Is this possible?**
The FETs are "gate voltage drivable" so wouldn't it be possible to put a ~6-7V battery in series with the 14 V and tie this 20-21 V to the Q2(s) collectors (and the isolators collector).
**Or maybe this?**
Or perhaps, would it be possible to work around this using a similar PNP power FET such as http://ixdev.ixys.com/DataSheet/DS99969 ... 85T%29.pdf
in place of the top NPNs? How might this change the drivers? (I've torn apart a toy car with a NPN/PNP h-bridge but it's difficult to see the whole circuit to reverse engineer it.)
Angelo- Q2 is tied to 14V already (it's unregulated... i.e. battery)...
inserting resistor in emitter branch
Do you mean between Q2 emitter and Q1 gate? I'm not sure I know what you mean... It may just be a case of seeing the connection dots where there aren't any on the schematic (I know they're stupid small).
p.s. RoboJoust is sparkfun's sumo-ish robot competition (http://www.sparkfun.com/commerce/produc ... ts_id=9523
The reason for this circuit is an attempt to avoid paying $70 for 3 5-10A motor drivers when really the components needed only cost ~$20 + brain-power