Re: BOSS stepper driver transistor

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Roy J. Tellason"
<rtellason@b...> wrote:

> On Thursday 26 May 2005 06:49 pm, Polaraligned wrote:
> > I lost one of my Z axis drive transistors. Probably because I am
> > running a 208 volt machine on 240v. I found a tap to lower
> > the voltage to all the electronics except the 3 phase transformer
> > that powers the steppers. The other two axis have been running
> > like a charm at 240v.
> > The original transistor is a STA 7018. This crosses to a NTE 165.
> > I have
> > some 2N3055's handy. They are MUCH more hardy than the original
> > transistors. Maybe by 10x in the power dissipation department.
> > Can I use one of these? It exceeds the ratings of the original
> > in every category. Suprisingly, all the transistor date codes
> > on the machine match the time of manufacture. I thought these
> > things were supposed to pop like popcorn?
>
> Dunno about how they're supposed to pop, transistors have different

failure

> modes...
>
> What supply voltage is this circuit operating at? I don't have data

here on

> the STA7018 (feel free to send a datasheet along to me if you have

one) but

> the 2N3055 is a 60V part, which makes me wonder.
>
> The 2N3055 is a pretty common power transistor, but there are a LOT of
> beefier parts out there these days.
>
> How did the bad transistor fail? Open? Shorted? Something else?

You are right Roy. The 3055 is a 60V part. It just has a much
higher current rating though. I do not have data on the STA 7018, but
it does cross to a NTE 165 which is easy enough to look up. Just
google it. The NTE 165 is a 1500v part. Probably overkill. The
transistor failed in shorted mode. About 12 ohms
between base and emitter, and 12 ohms between base and collector.
I am trying to get away with something I have in stock, or Radio
shack has. I may have a NTE 165 in stock, but it will take a LOT
of looking as I have moved and not unpacked all my electronics
components yet.

Thanks,
Scott