WTD: Small signal NPN, HFE >= 200 at Ic < 2uA...

[Joerg]

Joerg a écrit :


Yep. I think I've measured one too. IIRC the PNP was marginally better,
but by a tiny by four cut hair.

If you guys need low noise transistors a lot check out the BCX70K that
John recommended. I am still leaning towards that one, mostly on account
of its low cost:
http://rocky.digikey.com/WebLib/Infineon/Web Data/BCW60_BCX70.pdf

BCW71 would be the complementary PNP.

 

[Greg Neff]

FWIW,
From an old notebook,
some crude tests:

. +5.1V
. -+-
. |
. 1M
. | Figure 1.
. .----+ Test Circuit
. | |
. 100M |
. | |
. | |/
. '--|
. |>e
. |
. |
. ===
. GND

Mfr type ic (uA) Hfe
--- --------- ------- ---
ITT 2n3904 #1 1.89 69
FSC 2n3904 0.18 4
ITT 2n3904 #2 1.01 27
ITT 2n3904 #3 1.01 28
ITT 2n3904 #4 1.01 56
Mot 2n3904 #1 2.30 92
Mot 2n3904 #2 2.92 150

Mot MPSA18 #1 3.93 374
Mot MPSA18 #2 3.95 383
(note that Vce is only 1.1V.)

KTC3198 #1 3.43 228
KTC3198 #2 3.45 231



Just for fun:

. +5.1V
. -+-
. |
. .----+ Figure 2.
. | | Test Circuit
. | 1M
. 50G |
. | |
. | |/
. '--|
. |>e ib=93pA
. |
. |
. ===
. GND


The above was duly air-wired in
recognition of the small currents
involved. d(ic)/d(ib) rather than
static gain was measured to increase
confidence and reduce leakage
current effects.

Mfr Part ic d(ic)/d(ib)
--- ---------- ---- -----------
Mot MPSA18 #1 61nA 721
Mot MPSA18 #2 79 816

ITT 2n3904 #1 8.2 5
(dirty, leaky, used part, icbo=3.8nA)

KTC3198 #1 18 189
KTC3198 #2 18 195

Mot BC547B #1 18 189
Mot BC547B #2 16 174
Mot BC547B #3 18 189

Best regards,
James Arthur

Cool! Thanks for digging and sharing the data.


================================

Greg Neff
VP Engineering
*Microsym* Computers Inc.
[email protected]

 

[Greg Neff]

Well, it looks like there are some good candidate transistors out
there, so I'm comfortable with this working. However, I will
recommend to the customer that they not do this, because leakage
currents around this circuit will introduce unacceptable errors.


================================

Greg Neff
VP Engineering
*Microsym* Computers Inc.
[email protected]

 

[Joerg]

Well, it looks like there are some good candidate transistors out
there, so I'm comfortable with this working. However, I will
recommend to the customer that they not do this, because leakage
currents around this circuit will introduce unacceptable errors.

Looks like this would have to be potted up. Can they do that? Else the
slightest amount of conductive deposit could cause a problem. Like a
soot-belching school bus roaring by (when do they learn how to build
Diesels?).