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Old 11th May 2007, 11:18 PM   #31
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Hi Fotios

can I add to your list of parameters that one good way to characterise a transistor is the Gummel plot which is basically a plot of log(Ic) and log(Ib) versus Vbe. This shows in one curve the exponential (which is linear on a log scale) and resistive effects due to high bias, epi etc. and would be the best recommendation for matching, but it is often hard to spot gain differences when they are small variations around 100, so a plot of gain versus log(Ic) shows this very well. It is rather surprising that many data sheets used to show Vbe's for Ic and Ib on a linear scale, which was virtually no use at all...but sometimes you were lucky and manufacturers plotted different Ic scales, which helped a bit. Unfortunately, as spice models appear to have become more important, data sheets appear to be becoming mere skeletons of the device spec...

For gain matching of course it is as Andrew T pointed out that the Ic vs. Vbe is important for quiescent current, but a matched pair/set of transistors ought to match at all currents/Vbe's!

I'm guilty of not using the capital letters for hFE - sorry, you're quite right, but I of course meant hFE. But a pair or set of matched devices will also have equal hfe's!

input resistance of a transistor has to be ac really, because it changes so rapidly with bias, it makes no sense as a fixed value, and even for max. Vbe this might not be a good approximation in a class B output stage...and for class A stages, the operating input resistance (hie) ought to be used, as a guide to the performance (back of the envelope calculation) but there again, simulators will use whatever the value is at the time...



cheers
John
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Old 12th May 2007, 02:33 AM   #32
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Quote:
TI also shows how to do it with their power opamps (OPA549) which have a current limit pin and can source amps:
Jackinnj ,
Can you point me to Ti's tech-ref on this?

THX
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Old 25th May 2007, 04:29 PM   #33
locky_z is offline locky_z  China
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Default My intelligent semiconductor characteristic curve project

I use LTC1090(ADC) and M62359(DAC) with C++Builder software develop this curve.
It can measure PNP or NPN and N(P)MOS ,JFET,zener/diode/3-termination Reguregulate / opto-isolator

can draw Vce(Vds)->Ic / Ic->Hfe / Vbe(Vgs)-Ic / Ib->Ic / diode's Vd->Id / 3-termination Reguregulate's Vi-Vo, Io->Vo curve

such as the NPN2SC3519Vce->Ic curve result is below

My old project diy link is
http://bbs.hifidiy.net/viewthread.php?tid=31462


and now ,I use ADS7871+M62359 to do it again.
http://bbs.hifidiy.net/viewthread.php?tid=66451
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Old 25th May 2007, 04:40 PM   #34
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Quote:
Originally posted by head_spaz


Jackinnj ,
Can you point me to Ti's tech-ref on this?

THX
the current limit pin would be difficult to use for micro-amps it turns out.

Locky_Z == project looks good.
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Old 25th May 2007, 04:46 PM   #35
Nordic is offline Nordic  South Africa
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http://translate.google.com/translat...language_tools

Use google translate from Korean to english to read above links.
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Old 25th May 2007, 05:02 PM   #36
locky_z is offline locky_z  China
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My link is Chinese
http://translate.google.com/translat...language_tools
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Old 25th May 2007, 05:04 PM   #37
Nordic is offline Nordic  South Africa
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lol it translated with the korean, but it sounded funnier than usual... you win...
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Old 26th May 2007, 12:51 AM   #38
locky_z is offline locky_z  China
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My Project to matching transistor is powerful.
It not only demonstrate the same type transistor curve, but also can shows the complementary transistor curve

The picture show measurement Vgs->Id curve of my five 2SK246GR and five 2SJ103GR the
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Old 26th May 2007, 07:57 AM   #39
Nordic is offline Nordic  South Africa
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Do you have the PCB available for downloading?
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