GM-20 Driver

[teknofon]

I´m building a driver for GM-20s
using a BTS412B2 highside power switch

now my problem
the bounce back makes the flag resonate
how do i prevent it from bouncing around?

[DMills]

If you need speed, use current mode drive by sensing the current with a low value resistor and feeding it back into the (linear) drive amp.
The circuit of the original GS driver card is around on the net and will demonstrate the trick (But I would probably use a L165 or similar power opamp these days).

If the basic speed is OK and you just want to kill the mechanical resonance, try putting a short across the galvo once the drive is removed. You might think about a zenner diode in anti parallel series with a 4001 or something if you are using unipolar drive.

Regards, Dan.

[teknofon]

what is "anti parallel series"

should i do like this

[teknofon]

wouldn't a diac in parallel with the gm20 work?

[DMills]

wouldn't a diac in parallel with the gm20 work?

You have the diodes the wrong way around, the idea is that the back EMF is limited by the zenner (while the zenner drops a few volts to absorb the energy from the magnetic field) and the 4001 prevents the zenner acting as a normal doide in the forward direction.

You probably already have a clamp diode in your circuit? This should replace it.

Regards, Dan.

[teknofon]

what zener do you suggest?

[teknofon]

can i put a capacitor in parallel to the gm20
to filter out it´s self resonation?

[teknofon]

something like this?

[mixedgas]

Dmills is right, these are current driven, and they store copious amounts of energy.


Put 20 ohms resistive in parallel across the coils if they are in series, damps nicely.

Otherwise build something like a102 drivers with derived damping.


http://www.camtech.com/archive/A102_AX200.pdf

most people just put a hefty reverse diode across the coils.

Steve

[teknofon]

there is already a freewheel diode in the BTS412B2
but it doesn´t help

should i put the resistor like this in parallel?
is 1w resistor ok or should i go for 10w?