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Old 7th April 2011, 06:18 PM   #1591
artu is offline artu  Chile
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Yes I experienced the same, a quite stable design with the BD's (all BJT, no mosfet) turns unstable when replacing BD139/140 with MJE340/350, it is necessary to add lots of Miller capacitance to stabilize, I guess that the MJE's has a less doped collector (350V Vceo) that induces huge Miller capacitance variations. So for less than 80V swing go BD's, also THD can be 1 order of magnitude lower.
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Old 8th April 2011, 10:12 AM   #1592
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Quote:
Originally Posted by lineup View Post
MJE340/350 are good for higher voltage.
Otherwise I prefer BD139/140.
Think it is the higher gain that makes BD139/140 win over MJE340/350.

Many amplifiers have lower voltage than 80 Volt, the max of BD139/140
I have tried both options in SPICE amplifiers.
And BD139/140 gets substansially lower THD distortion than MJE340/350.
Hi lineup,

Yes, the BD139/140 are good VAS devices. I'll be including models of them in my upcoming next release of device models to my web page at CordellAudio.com - Home.

Cheers,
Bob
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Old 9th April 2011, 01:01 AM   #1593
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Default Poor models

As many of you know, I often complain about the shortcomings of transistor SPICE models provided by vendors. Here's an example that certainly competes for the prize. This morning I was working on the BD139/140 models. I usually start with models from one or more manufacturers and SPICE them on several testbench circuits and compare the results to the datasheet and/or measurements I have made. The SPICE models for these devices from a well-known semiconductor company that will remain nameless had the usual set of numbers to four or so significant digits, but did not contain at all one of the most parameters: TF, which defines ft. What frustration!

Cheers,
Bob
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Old 9th April 2011, 08:38 AM   #1594
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Default Design Support

Quote:
Originally Posted by Bob Cordell View Post
. . . did not contain at all one of the most parameters: TF, which defines ft. What frustration!
That spec seems to be missing from several prominent manufacturers' Data Sheets, too - so perhaps the model maker is simply reflecting that omission.

Quote:
As many of you know, I often complain about the shortcomings of transistor SPICE models provided by vendors.
The quality of SPICE models in general could become a never-ending rant. On more than one occasion I have been heard to say something like, "Yes, I know that the CAD/CAE program cost as much as an engineer's salary, and you ran it on a Personal Confuser that cost more than my car . . . BUT . . . No, in spite of what the simulation says, that uA741 will NOT supply enough current to jump-start a locomotive!". (Yes, there ARE opamp SPICE models that have no limits on output voltage or current.)

The factors leading to this shameful situation are legion. About 15 - 20 years ago I got the impression that some manufacturers wanted to have SPICE models of their parts just so marketing could say, "We have SPICE models.".

A few incarnations ago I worked with an engineer who said that composing SPICE models had been his assignment in a summer job while a college student. He worked from Data Sheets, and wondered if anybody had ever verified his work against real parts.

In 1975, there may have been some justification for publishing "abbreviated" models. Since your department was probably charged by the millisecond for CPU time on the System 360/65, it made sense to have a simplified model that would compute quickly and tell you if things like bias points and basic operation were correct . . . and then you'd use a more complete model to investigate the places where your sliderule and nomographs said there might be a problem. That work environment ended about the time a math coprocessor became available for the PC/AT.

With RARE exceptions (Burr-Brown comes to mind, but I'm too lazy to verify it at the moment) SPICE models almost never tell you what characteristics are, or aren't, modeled - or how accurately. Users are left to wonder if a simulation anomaly is real, or an artifact of the simulation process, or the result of some un-modeled behavior. I believe some of Analog Devices' products have sets of models covering nominal, worst-case, and temperature extremes of behavior, but I don't recall others who followed suit. Again, the end user is (at best) stuck with creating and executing a process for model verification before he can use the model for serious design work.

It's bad enough that simplified, and inaccurate, models from 20 or 30 years ago will probably survive (thanks to the Internet) through a Nuclear Winter. Some seem to have acquired the ability to spontaneously regenerate when they were handed out with the "free" versions of P-CAD, Electronics Workbench, et al. Data Sheets seem to get revised every few years (at least to correct typos), but once a SPICE model has been created it's probably never revised. What irks me even more is that even rather recent models suffer the deficiencies of the early efforts. C'mon, guys - it was in the early 1990's (!!) when Alexander and Bowers (at PMI/Analog Devices), and Biagi, Baker et al (at Burr-Brown) published App Notes that make significant corrections and much-needed enhancements to the Boyle modeling approach for opamps.

p.s. - I have started putting the oscillator section of your THD Analyzer into LTspice.
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Old 9th April 2011, 10:28 AM   #1595
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According to info provided to me from phillips the BD139 is BC639 in a TO126 case. The ft of bc639 is 100 Mhz at 10ma and cob figures are also available for the BC639 which is around 7pf at -10v Vcb. Likewise the BD140 is the BC640. This was done to achieve higher dissipation. These transistors might be old but they arent half as bad as some think them to be.
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Old 9th April 2011, 12:11 PM   #1596
wahab is offline wahab  Algeria
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Well, i have 16 basic models just for the 2N2222 , not counting
a bunch that comes from diverses manufacturers...
-55 C
-55 C RAD1
-55 C RAD2
-15 C
-15 C RAD1
-15 C RAD2
27 C
27 C RAD1
27 C RAD2
27 C RAD3
27 C RAD4
27 C RAD5
27 C RAD6
75 C
75 C RAD
125 C

Last edited by wahab; 9th April 2011 at 12:15 PM.
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Old 11th April 2011, 02:42 PM   #1597
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Quote:
Originally Posted by dchisholm View Post
That spec seems to be missing from several prominent manufacturers' Data Sheets, too - so perhaps the model maker is simply reflecting that omission.

The quality of SPICE models in general could become a never-ending rant. On more than one occasion I have been heard to say something like, "Yes, I know that the CAD/CAE program cost as much as an engineer's salary, and you ran it on a Personal Confuser that cost more than my car . . . BUT . . . No, in spite of what the simulation says, that uA741 will NOT supply enough current to jump-start a locomotive!". (Yes, there ARE opamp SPICE models that have no limits on output voltage or current.)

The factors leading to this shameful situation are legion. About 15 - 20 years ago I got the impression that some manufacturers wanted to have SPICE models of their parts just so marketing could say, "We have SPICE models.".

A few incarnations ago I worked with an engineer who said that composing SPICE models had been his assignment in a summer job while a college student. He worked from Data Sheets, and wondered if anybody had ever verified his work against real parts.

In 1975, there may have been some justification for publishing "abbreviated" models. Since your department was probably charged by the millisecond for CPU time on the System 360/65, it made sense to have a simplified model that would compute quickly and tell you if things like bias points and basic operation were correct . . . and then you'd use a more complete model to investigate the places where your sliderule and nomographs said there might be a problem. That work environment ended about the time a math coprocessor became available for the PC/AT.

With RARE exceptions (Burr-Brown comes to mind, but I'm too lazy to verify it at the moment) SPICE models almost never tell you what characteristics are, or aren't, modeled - or how accurately. Users are left to wonder if a simulation anomaly is real, or an artifact of the simulation process, or the result of some un-modeled behavior. I believe some of Analog Devices' products have sets of models covering nominal, worst-case, and temperature extremes of behavior, but I don't recall others who followed suit. Again, the end user is (at best) stuck with creating and executing a process for model verification before he can use the model for serious design work.

It's bad enough that simplified, and inaccurate, models from 20 or 30 years ago will probably survive (thanks to the Internet) through a Nuclear Winter. Some seem to have acquired the ability to spontaneously regenerate when they were handed out with the "free" versions of P-CAD, Electronics Workbench, et al. Data Sheets seem to get revised every few years (at least to correct typos), but once a SPICE model has been created it's probably never revised. What irks me even more is that even rather recent models suffer the deficiencies of the early efforts. C'mon, guys - it was in the early 1990's (!!) when Alexander and Bowers (at PMI/Analog Devices), and Biagi, Baker et al (at Burr-Brown) published App Notes that make significant corrections and much-needed enhancements to the Boyle modeling approach for opamps.

p.s. - I have started putting the oscillator section of your THD Analyzer into LTspice.
Hi dchisholm,

I agree with everything you have said. The situation is probably worse with things like op amp macro-models than with transistors. I believe that with transistors, they just subcontract out the model generation and a machine with some algorithm that does not necessarily apply any common sense just spits out silly numbers with many significant digits. Then the vendor just throws the model over the wall without even checking to see if the model yields results that are in reasonable accordance with the device spec sheet. No regression testing is done, and much better results would be achieved if even a college summer student was hired to look at the models. I guess the vendors just don't care.

Cheers,
Bob
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Old 11th April 2011, 02:58 PM   #1598
AndrewT is offline AndrewT  Scotland
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I wonder if it is simply cheaper to give out free samples than to give out accurate data?

How much does one million free samples cost ex factory, compared to models/data?
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Old 11th April 2011, 03:16 PM   #1599
davada is offline davada  Canada
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Default Transistor models

What would be cool is a jig which connects to a computer that would take the measurements, dump the measurements to a file and generate a spice model.

David.
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Old 11th April 2011, 09:53 PM   #1600
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Quote:
Originally Posted by davada View Post
What would be cool is a jig which connects to a computer that would take the measurements, dump the measurements to a file and generate a spice model.

David.
Hi David,

I'm guessing that is what the manufacturers are doing, but without much success. Maybe they just need better algorithms. Even if they did not do modeling measurements and just extracted the data from the curves in their datasheets, and could create model parameters that would reasonably match the datasheet info, that would be nice.

Cheers,
Bob
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