Re: [CAD_CAM_EDM_DRO] Re: BOSS stepper driver transistor

On Thursday 26 May 2005 07:31 pm, Polaraligned wrote:

> --- 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.

It was a pretty beefy part in its day, but there are lots beefier ones
available these days.

> 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.

That sounds like a horizontal output transistor application, which would make
me wonder. Those have tremendously high voltage capabilities (800v-1500v
being typical) but at a cost in both gain and current-handling capability.
I'd do a search and see if you can't find data on the original number, that
cross doesn't sound right to me.

> Probably overkill. The transistor failed in shorted mode.

Probably too much current flow, then. Too much voltage (spikes, etc.) often
fail open.

> About 12 ohms between base and emitter, and 12 ohms between base and
> collector.

And probably zero ohms collector-emitter.

> I am trying to get away with something I have in stock, or Radio
> shack has.

That sure ain't much these days!

> 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.

I hate it when that happens! :-)

I have a *big* transistor chart that I've worked up as an HTML page. The
current one is even bigger than the one that's online, and I have a bit of
work to do before I put my version into the web space my ISP makes available
to me, but you can see a slightly older version of it at this URL:

http://ignatz.alojamentos7.com/transistors.html

That version, if I remember correctly, is somewhat over 600K in size! The
newer version that I'm still working on is over 700K. Either way they'll
take a while to load... Anything that shows up in there as a link I have a
datasheet for, but the chart itself should be useful for getting a handle
on all sorts of different parts. If you have data on stuff I don't show data
on, by all means let me know offlist and we'll fix that. I also have some
other pages I'll be putting up, on diodes and chips and stuff, once I find
the time to get around to it.

Hope this helps...