Hello,

This seems reasonable, but I have a few questions.  First, I assume a small
resistor is on the order of milli-ohms.  Secondly, given such a small
resistor value what power rating does it require?  Theoretically, when power
is first provided to the motor (i.e. the H-bridge is turned on) the motor
resistance is 0.  Thus, there is a very large current across this resistor.
Now, the time must be very small (or there would be a short to ground
without the current sense resistor).  If I hope to run my controller at 24V
and current limit at 20A, do I really need a sense resistor capable of
480W!?



> > My questions is how to I add current and thermal limiters to an
H-bridge?
>
> The easiest way to add current limiting is to add a small resistor in
series
> with the H bridge.  It should only drop a small fraction of the supply
> voltage at full current.  Just enough to trigger a comparator to the
> accuracy you need.  This goes into the PIC as an input, which causes it to
> shut down the H bridge, go into error mode, or whatever.

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