Re: [CAD_CAM_EDM_DRO] Stepper Motor Driver

the ir series are hexfets - very special fets.
i have the international rectifier designers handbook
here, so i'll quote it:
"The integral body-drain diode is a real circuit
element, and it's current handling capability is
typically as high as that of the transistor itself."
i admit i have never scoped it, so i don't know first
hand just how fast it is. i can say i've never had a
hexfet powerfet fail on me from driving steppers with
it.
i'd totally like to correct my understanding if it's
wrong, though, if you have any good info that
clarifies this.


--- Jon Elson <elson@...> wrote:

> 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
>
>
>
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