[Balderscape]

Hi,

I am looking into designing and building a stepper driver that is mains powered.

I have been along the lines of using a PFC circuit to generate 400VDC from 85 - 265VAC input, and then either PWMing the 400VDC through a H-bridge into a stepper coil, or using a Buck converter to step down from 400VDC to 30-100VDC suitable to then feed into a H-bridge to drive the stepper.

Has anyone done this approach before?
Are there any pointers or reasons for certain failure with this approach?
Is there an electrical isolation requirement in stepper supplies that will be not achieved through this method and if so is double insulation a suitable other option?

If anyone can lend advise or point me in the right direction I would be most appreciative.

[pminmo]

Depends on the stepper motor itself, how your going to use the "result" of your circuit, etc. (Rough numbers follow for explanations) For example if the coil voltage of the motor is 1.2V you wouldn't want a supply voltage of more than 30V.

As to using the mains without isolation it can be done, but you definitely need to know what your doing. Once aspect is where is 0V. Because a main is hardwired back into the facility power, depending on the facility the neutral can be +/- 0V by several volts. So any control signal references must isolate or follow the resultant DC negative.
The other aspect is failure and safety. If the return goes open, your DC negative will then raise to the potential of the rectified DC of the mains.

It's not something I'd do, or recommend doing. Kind of like having a loaded gun in the workshop with the safety off. As long as it stays put there is no harm, but what happens if an earthquake strikes while your in the workshop...........:-)