Low power consumption.
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Greg Neff VP Engineering
*Microsym* Computers Inc. snipped-for-privacy@guesswhichwordgoeshere.com-- Posted via a free Usenet account from http://www.teranews.com
I have to have surface mount, but thanks for the suggestion.
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Greg Neff VP Engineering
*Microsym* Computers Inc. snipped-for-privacy@guesswhichwordgoeshere.com-- Posted via a free Usenet account from http://www.teranews.com
"Fred Bartoli" wrote in message news:461421ec$0$23627$ snipped-for-privacy@news.free.fr...
MMBT5089 is there.
Why should the MPSA18 be better than the 5089? Just curious. The noise curves don't look promising, although the 1/f corner is clearly wrong for the 100uA/200uA cases, so maybe there are other errors.
Regards Ian
OK, checked it again.
Actually it was ZTX718 (PNP) not the ZTX618 (NPN)
Tested the same one I did some time ago, but when going at 10mA, the LF noise appeared abnormally high, and somewhat poppy. I don't remember this from previous test, so I also tested another one at 10mA and I might have zapped a bit the BE junction from manipulation. Also checked a 737 at 10mA for comparison.
Noise in nV/rtHz:
---------- ZTX 718/A ------------- ZTX718/B -- 2SB737 @IC= 3mA 1mA 0.3mA 10mA 10mA 10mA F=10kHz 0.6 0.8 1.1 0.5 - 0.45 F=1kHz 0.6 0.8 1.15 0.6 0.55 0.45 F=100Hz 0.8 0.85 1.2 0.9 0.65 0.45 F=30Hz 0.9 0.9 1.25 1.6 0.65 0.45 F=10Hz 1.05 1.05 1.4 3.3 0.9 0.7
-- Thanks, Fred.
Thanks, Fred. That's pretty darn good. Except that the ZTX718 doesn't seem to come in SMT and Digikey doesn't carry the 2SB737 at all :-(
I guess we could fit in some thru-hole parts if there is a copelling reason. And your table above sure is a compelling reason.
-- Regards, Joerg http://www.analogconsultants.com
Yes they exist. The part number is FMMT718. ZTX is for their eline thermally enhanced 'TO92', FMMT is for their SOT23 package and digikey has them :
but these are the PNP. I think you wanted the NPN:
The 2SB737 has been obsoloted some times ago, so no surprise for digikey. But is still available through the grey market. Here, I bought mines in France at 20cts a pop, unit price. Toshiba and hitachi/renesas still have some interesting low noise replacements. Digikey even have the renesas 2sa1084 in stock. Sorry that's TO92.
-- Thanks, Fred.
Does your application have a self-test? When you deal with designs on the edge, you are more likely to find defective parts. I never worked anywhere that did discrete devices, so I don't know the test flow. If there is any testing at all, I'd suspect IC in the mA range, not uA range.
Can you let me know which one that was? Digikey's search terms expire within minutes. One of those non-sensical "features" of their search engine.
TO would not be nice but ok. Gray market stuff is a big no-no though.
-- Regards, Joerg http://www.analogconsultants.com
Ooops! FMMT718 for the PNP, FMMT618 for the NPN.
2SA1084 for the renesas PNP (TO). The NPN is 2SC2545/2546/2547 but I didn't see them.-- Thanks, Fred.
Thanks, Fred. I guess the 618 must be the "similar noise specs" companion to the 718 then.
Many Japanese transistors are very hard to find in the US. It was similar in Europe when I lived there.
-- Regards, Joerg http://www.analogconsultants.com
Yep. I think I've measured one too. IIRC the PNP was marginally better, but by a tiny by four cut hair.
-- Thanks, Fred.
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
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:
BCW71 would be the complementary PNP.
-- Regards, Joerg http://www.analogconsultants.com
Cool! Thanks for digging and sharing the data.
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Greg Neff VP Engineering
*Microsym* Computers Inc. snipped-for-privacy@guesswhichwordgoeshere.com-- Posted via a free Usenet account from http://www.teranews.com
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.
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Greg Neff VP Engineering
*Microsym* Computers Inc. snipped-for-privacy@guesswhichwordgoeshere.com-- Posted via a free Usenet account from http://www.teranews.com
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?).
-- Regards, Joerg http://www.analogconsultants.com
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