Re: [CAD_CAM_EDM_DRO] Question re: about current control schematic

grantfair2001 wrote:

>Jon, one limitation of this circuit which you point out is the absence
>of the ability to vary the current delivered depending on the number
>of phases switched on. Is there any reason this could not be added
>with different VR 1 values switched in or out with a 4066 by
>appropriate logic which responded to number of phases turned on?
>
>

In full step, there is always one transistor of each motor phase turned on.
But, when one of the transistors swithes off, and the other one for that
phase is switched on, the total current is set to be constant. As the
current
in the switched phase is ramping down to zero, and then reversing, the
current in the other phase goes up to 2X for a moment, then ramps back
down as the switched winding picks up the current. this is horrible!
It may work for those 1" square motors in floppy drives, but it will
give horrible high-speed performance with big motors. It is just
a bad circuit, because it mixes the current in both phases, and because
it is unipolar. The whole basic idea is just wrong, outdated, 1960's
logic, and any attempt to improve it is like automating the buggy
whip on a horse carriage.

Jon