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Old 12th May 2009, 11:04 AM   #1
icko is offline icko  Sweden
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Default small signal transistor

I'm playing around with spice and trying to choose a small-signal transistor to use for an amp project.

Right now i am using the common 2N5551/2N5401. Which I like becouse of the high voltage tolerances.

But it would be nice with some transistors with higher beta, anybody that can give me some tips? preferably some were spice models are available.

I've looked at BC107/BC177 which looks sweet to me, but they have a breakdown voltage of 40-50V. And i was thinking of using +-63V supplies so i am not sure I could use these.

I suspect that this have been up for consideration before but I cant find any good threads.


Thanks

Icko
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Old 12th May 2009, 11:48 AM   #2
AndrewT is offline AndrewT  Scotland
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do you need >=63Vce0?
or >=126Vce0?
or some Vce0 that is much less?

How far does your 63Vdc vary with loading and with mains voltage variations?
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Old 12th May 2009, 06:44 PM   #3
icko is offline icko  Sweden
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actually i haven't simulated the diff amp yet. mostly i was thinking around it since i saw the datasheet on the 2N5551, 2N5401.

I'm guessing that VCEQ is less than 40V for the transistors, but
i should probably simulate first and ask questions later...=)

Anyway i found 2SC2240 and 2SA970 which seem good enough for me.

but no spice model for the toshiba 2SA970. After googling it seems as there is none from toshiba only zetex.
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Old 12th May 2009, 07:03 PM   #4
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Try k2sa992 and their complements from fairchild.
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Old 12th May 2009, 07:09 PM   #5
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Quote:
[i]Anyway i found 2SC2240 and 2SA970 which seem good enough for me.

but no spice model for the toshiba 2SA970. [/B]
.MODEL 2SA970 PNP(Is=465.4f Xti=3 Eg=1.11 Vaf=57 Bf=407.6
+ Ise=4.683p Ne=2.051 Ikf=.3998 Nk=1.192 Xtb=1.5 Var=100 Br=1
+ Isc=465.4f Nc=1.048 Ikr=6.032 Rc=2.343 Cjc=11.59p Mjc=.4014
+ Vjc=1.155 Fc=.5 Cje=5p Mje=.3333 Vje=.75 Tr=10n Tf=1.252n
+ Itf=1 Xtf=0 Vtf=10)

.MODEL 2SC2240 NPN(Is=99.13f Xti=3 Eg=1.11 Vaf=422.2 Bf=352.8
+ Ise=1.179p Ne=1.782 Ikf=.4704 Nk=.9631 Xtb=1.5 Var=100 Br=1.663
+ Isc=555.1p Nc=1.796 Ikr=5.85 Rc=.2032 Cjc=7.561p Mjc=.2472
+ Vjc=.3905 Fc=.5 Cje=5p Mje=.3333 Vje=.75 Tr=10n Tf=1.295n
+ Itf=1 Xtf=0 Vtf=10)
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Old 12th May 2009, 07:19 PM   #6
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Try this:

http://www.diodes.com/products/catal...p?item-id=611#
http://www.diodes.com/products/catal...p?item-id=646#
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Old 12th May 2009, 07:32 PM   #7
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Try the BC546/556, version B and C has more beta, but have less power..500mW
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Old 12th May 2009, 07:53 PM   #8
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I'm using 2SA1085 (suggested replacement for 2SA872) for my LTP. Don't know a lot about them other than low noise high gain and used in C-Audio amps!

Anybody else tried them?
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Old 12th May 2009, 08:49 PM   #9
mjf is offline mjf  Austria
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hello.
i think thel audio (germany) used 2sa1085/2sc2547 in their (phono)preamps (around 1996).........
greetings............
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Old 12th May 2009, 09:56 PM   #10
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I use a lot fo MPSA42 and MPSA92 in my designs.
They are 300V with a gain of around 45.

For VAS and its current source I use MJE340 and MJE350.

All are relatively cheap.
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