Stability of an amplifier under capacitive loading

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I was interested in the comment about inter-electrode capacitance in a BD139 and the comment that it could vary from manufacturer to manufacturer .


I could not find any actual info online when it came to the specifications by various companies but came across this-


Application Note No.024 by Infineon which is interesting -

AN024.fm - Parasitic_Capacitances_Bipolar_Transistors_AN024_Infineon.pdf
 
It is utterly reprehensible to call the indispensable interelectrode capacitances parasitic. Choose transistors with appropriate interelectrode capacitances for the task. The need for phase compensation is a palpable sign of functional disorder and design failure.
 
N101N ---if you feel so strongly about the AN of this company why don't you complain to them not me ?
I am sure they will "react " to your criticism , in a perfect/ideal world there would be no capacitance between elements but we are still waiting for the Klingons to land on earth with their "capacitance cloaking device " and put things right on planet earth.



An old English fable has King Canute standing at the sea edge saying " I am King and I command the tide to go back "----it refused and wet his feet --naughty tide ! That was in the 12th Cent. --nothing has changed .


Those statistic are needed in many engineering situations some vital .
 
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Parasitic capacitance or to put it more gently --"stray capacitance " is a natural occurring engineering phenomenon as we have not reached the stage of perfection.


When an engineer calculates the design of a tube/BJT/Mosfet etc etc this has to be taken into account when designing an electronic component .


Can you explain or show where "Perfect " components are manufactured in this world ?
Or are you complaining about the English grammar as being faulty ?


I could post long lines of university maths on this but will just post a Wiki explanation that keeps it simple.


If a Standard of perfection had been achieved then you could base your point on that , but it hasn't, people like engineering are not perfect.


A capacitor has resistance/capacitance/inductance --even a resistor contains other elements.




Parasitic element (electrical networks - Wikipedia)
 
Scott Wurcer is an engineer who designed high spec linear integrated circuits. He has mentioned parasitics - see Looking for a small signal NPN with no Quasi Saturation: MEASURED DATA.

The practical capacitance values end users get to work with can be found by looking up datasheets or SPICE .models for the device concerned. The relevant terms for capacitance in the latter are CJC and CJE.

You could have quantified your announcement with some information.
 
Take each word at a time -
Humongous -- large , supposed to be of American origin .
Parasitic an insect/organism/flea/intestinal worm / etc -- living off its host .
interelectrode --between electrodes or an electric chair customer .
Capacitance -- storage ability of your stomach or electrical energy .


Sounds like an old Western movie with the wagon fast talking barker selling fake medicine that "cures " baldness- headaches- gout-blindness-and every disease under the sun while beating his cane to attract attention in a small western town .



Of course the brave sheriff arrives and carts him off to jail ---and fines him.
 
Capacitance: the amount of electric charge - would be a more adequate definition. Unsurprisingly, the current handling capacity is directly reflected by the intrinsic capacitances.

knutn,
choosing the right transistor for that job is critical. You could try the KSA1381, but I personally only trust authentic manufacturing.
Although Hiraga selected the parts with great care, the 2SC1096 (NEC) is of the wrong type (high current handling capacity), my option would have been the 2SD758/2SB717 from the venerable Hitachi.

Also, keep in mind that the (input & output) load is the extremely complex product of inductive and capacitive reactance. In this and other respects, your software won`t get you anywhere.

mjona,
maybe you think that paying attention to details is not worth the hassle. Nevertheless, you still have a chance to build mediocre amplifiers.

Instead of audio amplifiers, people design oscillators and voltage regulators, not so seldom inspired by influential authors. It should stand to reason that amplifiers with instability issues cannot have good (high frequency) response.
 
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