Re: SERVOs & EMC

Bertho Boman wrote:

> From: Bertho Boman <boman@...>
>
> Very good description Jon!
>
> Re Floating current sense resistor:
>
> You might want to consider two grounded current gain resistors, one in each leg of the bridge and an analog switch to monitor
> the current going forward or reverse. It would eliminate the difficult floating measurement. I have also seen halleffect
> current sensors for this application.

Well, the circuit I have now requires only 9 components, which
doesn't seem bad. Unfortunately, putting resistors in
the ground legs of the lower transistors doesn't always do the
trick, as there is circulating current in the motor's inductance,
and you need to know which way the motor current flows, too.
I think the switching approach would be a good deal
more complicated, and I don't see how the current's direction
would be measured, in both cases (transistor on, and transistor
off).

Hall effect sensors have a lot of drift and hysteresis, which would
be undesirable. This circuit works VERY well, and I'm totally
happy with it.

Jon