[CAD_CAM_EDM_DRO] Energy dump (was: G201 modifications/update)

Hello list!

Though Mariss 'energy dump circuit' is quite simple it got me thinking. Wy not just use a zenerdiode with a Vz just under the drives maximum supply voltage and resistor in series to ground?

I realise that it might have to be a highpower zener (and resistor)depending on the current that is returned from the motor(s).
How high is that current anyway? About the same as the motors current rating or..?

/Henrik Olsson.

----- Original Message -----
From: Mariss Freimanis <geckohall@...>
> Hi,
>
> This happens automatically in a full-bridge drive because each pass
> transistor has a diode across it. Usually with bipolar transistors
> this diode is a discrete component, with MOSFETs it is intrinsic to
> the transistor. Furthermore, a MOSFET can "assist" the diode if the
> MOSFET is turned on because they are perfectly happy to carry current
> in either direction, unlike bipolar transistors.
>
> During deceleration kinetic energy must be removed from the motor and
> load. If the rate of energy removal is moderate, (gentle
> deceleration, and/or small load, low speed) the returned energy
> merely lessens the power supply load. If a large inertial load is
> rapidly decelerated from a high speed, (high rate of energy return),
> then power supply current can actually reverse direction and flow
> from the drive to the power supply.
>
> This "return" current will charge an uregulated power supply filter
> capacitor above the supply's rated voltage, and possibly above the
> drive's breakdown voltage.
>
> A while ago I posted in the "files" section of this group a circuit
> called "energy dump.pdf" which safely deals with this problem.
>
> Mariss