Check out the Servo amp/servo motor treatise on the Rutex site. Real good info.
From his treatise, in concert with some reverse engineering, here's my take:
The voltage rating is a function of several things:
1. Volatage rating of fets.
2. Whether they get power from power buss - on the regulated side of a PWM'd fet control, they seem to be essentially the same.
3. Back EMF.
Obviously, 60v fets won't work at 100 and 200v will be horrible overkill run at 60. Select accordingly and with enough capacity to handle surge current and voltage.
Back EMF can be absorbed by the epitaxial diodes inherent in the fets, if you have enough of them. It is better, however, to shunt with appropriate diodes. Make sure you have diodes w/enough voltage and current capability. Schottky's are preffered.
If the drive gets power from the same buss that feeds the motors, you usually have to double or tripple regulate to get from 180 to say 100 then to 20 and the to 12 or 5vdc that the drive circuit runs on.
A shunt regulator can do the grunt work to get from unreg to something liike 12-14vdc that an LM2940T5 will handle (these are MUCH better than 7805's - don't bypass with a diode!!!! for reverse insertion protection is in there already).
I tuned up some servo amps via using heavier versions of these very components and they seem to work fine - but you really have to dig into the controller to get to adjust current limits, over voltage, etc when you try such surgery - definitely NOT for the faint of heart nor electronically challenged...  |