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Avalanche transistors

J

Jeroen Belleman

Jan 1, 1970
0
The subject of avalanche-mode pulse generators comes up
here now and again. A colleague pointed out to me that
a Philips BFG541 transistor will avalanche nicely at
around 50V or so.

Confirmed. It's quite fast too: I measured a 150ps
risetime, using a Tek S-6 sampler plugin in a 7000 series
mainframe. It's a little over twice as fast as the 2n2369 I
usually select for this purpose.

I thought some people around here might like to know...

Anyone here know any other transistors that will also
avalanche fast? (I know of Zetex. Not so great.)

Jeroen Belleman
 
J

Joerg

Jan 1, 1970
0
Jeroen said:
The subject of avalanche-mode pulse generators comes up
here now and again. A colleague pointed out to me that
a Philips BFG541 transistor will avalanche nicely at
around 50V or so.

Confirmed. It's quite fast too: I measured a 150ps
risetime, using a Tek S-6 sampler plugin in a 7000 series
mainframe. It's a little over twice as fast as the 2n2369 I
usually select for this purpose.

I thought some people around here might like to know...

Anyone here know any other transistors that will also
avalanche fast? (I know of Zetex. Not so great.)

Sure, the Zetex cannot rival that. But: They have datasheet values for
lifetime. Do you know how long an avalanching BFG541 will last until it
goes phut?
 
F

Fred Bartoli

Jan 1, 1970
0
Tim Williams a écrit :
How well did the old germaniums do at that? Ive got plenty of PNPs,
but they're so leaky, how would you even tell if they've
avalanched? ;-) You'd have to switch the capacitor into it, there's
too much leakage for RC charging like you'd use a 2N2369.

(Fact: the old TO-5's were so leaky and so bad thermally that a
transistor, base open, in series with 1kohm and supplied by 15V, will
show hysteretic behavior like an SCR. As it heats up, it holds itself
right at the maximum power point (half +V) from leakage. Disconnect
it for a second and it cools off; forward bias it slightly and it
turns on.)

That's the best biasing scheme ever: no resistors at all.

Sure Joerg's drooling at that :)
 
S

Spehro Pefhany

Jan 1, 1970
0
No, it was a metal can, 2N107 I think. It wasn't photosensitive.

The early GE silicon transistors were packaged in a brownish epoxy and
were photosensitive.

John

Gawd, I can barely remember those- brown 'D' on the top with a black
disk at the base, wasn't it?


Best regards,
Spehro Pefhany
 
J

Joerg

Jan 1, 1970
0
Fred said:
Tim Williams a écrit :

That's the best biasing scheme ever: no resistors at all.

Sure Joerg's drooling at that :)

Some Si transistors had weird effects as well. Wasn't there some HP gear
where they had screwed up a reverse Vbe situation and the common "fix"
was to extinguish a Marlboro butt on top of the transistor once in a while?

Wonder what they do now that smoking is banned from all labs.
 
J

Jeroen Belleman

Jan 1, 1970
0
Joerg said:
Sure, the Zetex cannot rival that. But: They have datasheet values for
lifetime. Do you know how long an avalanching BFG541 will last until it
goes phut?

No, I don't. It's not specified for avalanche operation.
It's just a curiosity that may be useful.

Anyway, I also own a PSPL 4015. :)

Jeroen Belleman
 
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