BF469, 470, 471, 472 vs. MJE340/350 are ON better? - diyAudio
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Old 31st May 2002, 04:52 PM   #1
Electrons are yellow and more is better!
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Default BF469, 470, 471, 472 vs. MJE340/350 are ON better?

Hi!

Does anybody have reliable information about MJE340 and 350? I wonder about Ccb, Cbe and Cce capacitance. I wonder also about the transition frequency. The datasheets from ON are very poor in that sense.

BFxxx are 20 years old, have worked fine for but those types are only 2 Watts. Does anybody have anything good (or bad) to say about the ON-types? I'm mostly interested in technical performance, speed, noise, peculiarities.

My application is cascodes for diff input stages and high gain second stages, and of course high output power amps +- 70-100 volts.
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Old 31st May 2002, 05:23 PM   #2
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Default MJE340 MJE350

SRC=MJE340;MJE340;BJTs NPN;Power;300V 500mA
*SYM=POWBJTN
.SUBCKT MJE340 1 2 3
* TERMINALS: C B E
* 300 Volt .5 Amp SiNPN Power Transistor 08-16-1995
Q1 1 2 3 QPWR .67
Q2 1 4 3 QPWR .33
RBS 2 4 6.5
.MODEL QPWR NPN (IS=36.8F NF=1 BF=212 VAF=311 IKF=.5 ISE=138P NE=2
+ BR=4 NR=1 VAR=12 IKR=.75 RE=.663 RB=2.65 RC=.265 XTB=1.5
+ CJE=18.8P VJE=.6 MJE=.3 CJC=12.2P VJC=.22 MJC=.2 TF=7.65N TR=294N)
.ENDS
* MJE340, MOTOROLA BIPOLAR POWER TRANSISITOR DATA BOOK,
* 1992, P.3-876.
**********
*SRC=MJE350;MJE350;BJTs PNP;Power;300V 500mA
*SYM=POWBJTP
.SUBCKT MJE350 1 2 3
* TERMINALS: C B E
* 300 Volt .5 Amp SiPNP Power Transistor 08-16-1995
Q1 1 2 3 QPWR .67
Q2 1 4 3 QPWR .33
RBS 2 4 6.5
.MODEL QPWR PNP (IS=36.8F NF=1 BF=365 VAF=311 IKF=.225 ISE=96.8P NE=2
+ BR=4 NR=1 VAR=12 IKR=.337 RE=.663 RB=2.65 RC=.265 XTB=1.5
+ CJE=39.1P VJE=.6 MJE=.3 CJC=25.4P VJC=.22 MJC=.2 TF=7.65N TR=294N)
.ENDS
* MJE350, MOTOROLA BIPOLAR POWER TRANSISITOR DATA BOOK,
* 1992, P.3-880.
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Old 31st May 2002, 08:32 PM   #3
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I've used the 340/350 series in past designs with good results. Hfe fall off at higher temperature and current is one drawback.

Another nice set of transistors in a reasonable voltage range are the Zetx FZT696 and FZT796, as long as 180 - 200V is OK.

-Jon
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Old 3rd June 2002, 12:48 PM   #4
Electrons are yellow and more is better!
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Sorry, I'm not a SPICE-guy (yet). Can anyone decode the SPICE data for me, please?

The subject line (topic) became funny. I ment if the MJE-types are better than the BF-types. Of course, the MJE are better (in power and in current) but in what sence besides that?
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Old 3rd June 2002, 01:02 PM   #5
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Default Why you want to know SPICE a bit even if you don't use it...

A SPICE model is a mathematical description of the semiconductor behavior. A good SPICE model will give good insights into the behevior of the device, and it's nonlinearities as a function of voltage and current. (A "good" SPICE model is not always provided- many have shortcuts or simplifications- many parameters can be omitted, or incorrect, and the model still "works", after a fashion).

Besides it's usefulness in a simulator, if you chose to develop with simulation as an initial evaluation point for circuits, it's a very "compact" method describing in detail the device behavior- much more so than the many paragraphs of text which would be required to substitute, and which would be prone to ambiguity in comparison to the "numbers".

This may have been HarryHaller's "indirect" point, in addition to the actual information he provided. If you have a good grounding in semiconductor theory (math included), SPICE notation is a non-issue to learn. If you don't have a grounding in semiconductor theory, the rest of the discussion is a moot point, until you do. It's usually necessary to walk before running, yes?

Lastly, although it's helpful to have comments an information from others, there's no substitute in my experience for testing and characterizing the parts yourself - if you don't like On's curves, measure your own. And evaluate the performance in the circuit blocks you're considering using. I've built up a number of "standard" (for me) test fixtures with set operating conditions so I can easily compare devices in specific circuit functions, and evaluate distortion and bandwidth. This separates the wheat from the chaff pretty quickly.

Regards,

Jon
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Old 3rd June 2002, 01:15 PM   #6
Electrons are yellow and more is better!
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JonMarsh, I understand what you meen but sometimes it's much faster to know from datasheets and then design compared to testing. But if you know if a transistor has 10 MHz fT you can disgard it right away and save lots of time.
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Old 16th January 2004, 03:09 PM   #7
Bonsai is offline Bonsai  Taiwan
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Smile BF469/470

I'm doing some development work on an amp at the moment and have identified a problem with the MJE devices when used as the upper devices in a cascode configuration. If the amp is driven into saturation (i.e. clipping) it is prone to ringing as it comes out of clipping. If I run the simulation with the BF4xx devices (these were high speed, high voltage video amplifier transistors), the problem solved. I've actually had the problem on a prototype board and presumed the problem was due to stability problems. I now have reason to believe the issue is to do with higher base storage on the MJE devices - I ran a simple simulation and the MJE devices are quite 'sticky' and switch on and off after the BF4xx types. A Baker clamp does not solve the problem by the way.

I checked for the BF4xx parts on the Philips website - they are discontinued, and replaced with some similar SMD devices (SOT223 I think).

Does anyone know of a close equavalent to the BF4xx devices from another manufacturer?

I'm using LT Spice by the way.

cheers
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Old 16th January 2004, 03:47 PM   #8
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Do you have any anti-clipping (or anti-saturation) diodes?

Can you post the schematics?

One trick is to avoid total saturation with diodes.

I'm also after good TO126 or TO220 substitutes.
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Old 16th January 2004, 04:04 PM   #9
andy_c is offline andy_c  United States
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Default Re: BF469/470

Quote:
Originally posted by ACR
(...) A Baker clamp does not solve the problem by the way.(...)
Have you tried looking at the base currents in simulation to make sure the Baker clamp is working as it should? There's some discussion of this issue here:http://www.diyaudio.com/forums/showt...754#post298754 I had to do some special biasing to make sure the base voltage bias didn't get affected by the current in the Baker clamp diode, which can get rather large depending on the circuit topology.
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Old 16th January 2004, 08:54 PM   #10
jcx is offline jcx  United States
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since the signal in the collectors is current, input cascode devices can use series V dropping zeners or R||C

i haven't tried any but hi-V dmos might be interesting to explore in vas cascodes, Supertex (depletion mode too!) and Zetex have some fairly lo C devices up to 400 V
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