[sdiy] double transistors

[Mountain Man]

Thanks, Jim  - this is very helpful :)  And thanks to everyone else who replied.
Anyone have a circuit for testing they'd be willing to share?  I'd certaintly be
interested.

Elby


patchell wrote:

>     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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> * Visit:http://www.silcom.com/~patchell/
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