Re: [CAD_CAM_EDM_DRO] Stepper Motor Driver

juan gelt wrote:

>no, it will not self destruct.
>the international rectifier hexfets have a built in
>reverse diode that will handle FULL LOAD CURRENT.
>

The diodes will never be called on to conduct. The problem is that
at 20 V power supply, when the drive steps, the transistor that is
turning off will be exposed to about 40 V plus the inductive
turnoff on the leakage inductance, which is hard to predict. It
will force the transistors into avalanche breakdown. This is a
rough abuse of the transistors. A freewheeling diode connected
to return this current to the power supply would be a good addition
to the circuit.

>However, irfz is NOT the right choice - use IRLZ54.
>

Yes, this is a good point.

>these are made to run on logic level input.
>digikey has them.
>if you want a nicer circuit that's about as simple,
>grab the pdf from this link.
>http://robotstore.com/catalog/display.asp?pid=63
>

A better circuit for a number of reasons. The opto-isolation is a good
idea. It still doesn't have the freewheeling diodes, though.

Jon