[sdiy] double transistors

[patchell]

    You feed a constant current through the transistor and measure the Vbe.
Generally, you want to do this at two different currents.  I generally pick 500uA
and 5uA.  You measure and record the Vbe's for each transistor, and after you
have a bunch of them, you match the ones that are closest.  This proceedure is a
little tricky.  It is best done while the temperature in the room is not changing
very fast, as, this will affect the Vbe value.  You also have to avoid touching
the transistors with your fingers, as this will also warm them up and give you
incorrect readings.  Several people on the list have circuits for doing this.

MountainMan wrote:

> When people talk about "matching transistors", what do they mean?  How
> does one determine this?
>
> Thanks,
> Elby
>
> On Thu, 5 Apr 2001, Happy Harry wrote:
>
> > I got some sample quad transistors from Central Semiconductor...
> > a quad 2N3904 in a dip-14 package.  I need to check them for
> > matching. A quick check with a Fluke 8050A looks pretty good, but that
> > is at an absurdly low current level (can you say all curves meet at the
> > origin...)
> >
> > A LOT of these units are NOT on the same die... they are two trannys
> > in one package... they are probably sliced from the same wafer and might be
> > quite well matched by good fortune... no guarantee.
> >
> > These are probably better than gluing two 2N3904 face to face though,
> > unless you match them.
> >
> > Hehheh  NO match for MAT-02
> >
> > H^) harry
> >
> >
> >
> > >From: Trevor Page <trevor at resonance.fsnet.co.uk>
> > >To: harm jansen <polynipaam at yahoo.com>, synth-diy at node12b53.a2000.nl
> > >Subject: Re: [sdiy] double transistors
> > >Date: Thu, 5 Apr 2001 11:17:41 +0100 (GMT+01:00)
> > >
> > >Hi,
> > >
> > >Farnell stocks these components. I ordered these for exactly the same
> > >purpose (TB303 VCO, VCF) but they have been sitting on my desk for month
> > >since I've not taken the time to try them yet, so not sure how they
> > >perform. Actually, I didn't order the PUM components, but got the BC857s
> > >and BC847s instead. The PUMZ, PUMX and BC dual SMD devices are grouped
> > >together in the Farnell semi's catalogue.
> > >
> > >I also found Farnell's SMD tempco's useful...
> > >
> > >Trev
> > >
> > >
> > >----- Original Message -----
> > >From: harm jansen <polynipaam at yahoo.com>
> > >To: synth-diy at node12b53.a2000.nl
> > >Sent: Thu, 5 Apr 2001 10:44:06 +0100 (GMT+01:00)
> > >Subject: [sdiy] double transistors
> > >
> > > >
> > > > Hi All,
> > > >
> > > > While looking for double transistors I stumbled upon
> > > > some SMD double transistors that seem interesting for
> > > > applications where space is a problem.
> > > >
> > > > Philips semiconductor makes three kinds:
> > > > the first device is two NPN transistors in one package
> > > > the second device is two PNP transistors in a package
> > > > the third device is one NPN and one PNP in a package
> > > >
> > > > names: PUMX1 PUMT1 PUMZ1
> > > >
> > > > Does anyone know which company stocks these.
> > > > The only companies that I found where arrow and
> > > > pioneer
> > > > but the quantity that you have to take is quite large.
> > > > But the price is unbelievably low $0.063. This would
> > > > make the cost $189 not a lot for 3000 double
> > > > transistors.
> > > >
> > > > Harm
> > > >
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> >

--
 -Jim
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