> -----Original Message-----
> From: Morgan Olsson [SMTP:dlist@MORGANSREGLERTEKNIK.SE]
> Sent: Monday, March 10, 2003 12:06 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [EE] H-bridge problems
>
> < Schematic1.JPG >
> Add "free-wheeling diodes"  that means diodes across each of the four
> power transistors CE to protect them from reverse voltage, that the motor
> inductance couse when you switch them off.
>
> I have not analyzed your design thoroughly, by i think at least for th
> eupper trannys you should add BE resistors of a couple hundred ohms to
> make them switch off fast enough.
>
> /Morgan
>
That's exactly what jumped out at me when I looked at it.  There is nothing
to switch off either the lower or the upper transistors quickly.  Some form
of reverse voltage control such as freewheeling diodes is pretty essential
of course.

Regards

Mike


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