cctech Digest, Vol 68, Issue 45 - test-drb@ccmp.vtda.org

28 Apr 2009

On 4/26/2009, ard at p850ug1.demon.co.uk (Tony Duell) wrote:

...

Message: 1
Date: Sat, 25 Apr 2009 19:27:20 +0100 (BST)
From: ard at p850ug1.demon.co.uk (Tony Duell)
Subject: Re: Transistors...
To: cctalk at classiccmp.org
Message-ID: <m1Lxmay-000J3RC at p850ug1>
Content-Type: text/plain

   If you
wire two diodes in series (PN->NP), it isn't the same as a
 transistor (PNP), at all. 
 It is. A PNP is just the same thing as a PN-+-NP. 
In one sense it is, but I can assure you that if you connect 2 diodes
together in this way (no matter what sort of diodes you use), you will
not get a transistor. The resulting circuit will not show any current gain.

IIRC, what you need is a sufficiently thin base region (the 'N' in the
example you gave) that electron-hole recombination does not occur. You
can't join 2 n-type pieces with a bit of wire and get this.

  possible space wise anyway, not even considering
characteristics. But
 that don't change the fact that you get a working transistor with just
 two diodes. 

Excuse the bluntness, but that is utter and complete bollocks. You do
*not* get a transistor with two diodes. Tony's comment above is
correct, for a transistor to work, the base needs to be thin enough that
electron-hole recombination does not occur (to any significant degree at
least).

Two diodes connected back to back will never be anything but two diodes
connected back to back. No current gain *at all*.

...
 I am not convinces. If you have got this to work, can
you please tell me
what sort of diodes you used, and I will try to recreate it (if I see it
working on my bench, I'll be convinced!)

-tony

/Jonas