Theory discussion moved from Q/A

[audioguru]

From a practical, "I only have to build one of these, not 10,000...", it probably doesn't matter!!

Try measuring the current gain of a few hundred 2N3055 transistors to find one with a gain high enough to allow the little 2N2219 to be its driver in the power supply project.

Try ignoring the very high ripple when its output voltage is only 25VDC and its current is more than 2.5A.
The project is supposed to give 30V at 3A. It can't if not modified.
What about the absolute max voltage rating that is exceeded for its ICs? It is not recommended.

Noobies say the original project "works" without testing it properly.
Experts say the modified version works properly and excellently.

[indulis]

Try measuring the current gain of a few hundred 2N3055 transistors to find one with a gain high enough to allow the little 2N2219 to be its driver in the power supply project.

Try measuring the current gain of a few hundred 2N3055 transistors to find one with a gain that's at it's specifications min level!!! I'm sure "gain variation" follows a standard distribution and components with spec's out beyond 6 sigma are hard to find!!

I agree with you from a analytical perspective, but "theory" is just theory,  until proven otherwise. Until such time that as many non-fuctioning supplies are built as functioning ones because of minimum beta of the pass transistor, "your theory"  isn't supported by hard data, irreguardless of what "good design practices" tells us. You know... there a lot of places out there that design to "nomimal" specifications, because "statistical voodoo" says you can get away with it cost wise!!

[audioguru]

Until such time that as many non-fuctioning supplies are built as functioning ones because of minimum beta of the pass transistor, "your theory"

[indulis]

John,

As I said before, from an analytical standpoint I agree you. No one disputes that under certain conditions, the 2N2219 will smoke, but that will ONLY happen when the pass transistors Hfe is at it's minimum. So, unless you have statistical data, that you can post, from the 2N3055 manufacturers that shows beta distribution is something other than "standard", you haven't proven a thing... it's just theory again.  I couldn't find a 2N3055 data sheet that graphs Hfe at high Vce voltages (I looked at 6 different manufacturers)… know where I can find one??

[mik3ca]

...the 2N2219 will smoke, but that will ONLY happen when the pass transistors Hfe is at it's minimum.

You know, transistors can smoke alot easier than that. :o  Just be an idiot when connecting them.

In fact, if you connect the base of the 2N3904 to the positive of a high DC voltage source and the emitter to the negative of the same source, I can guarantee that it will malfunction. In fact, I can guarantee that some smoke will appear.

and why will they malfunction? because if we ignored the internal battery resistance, the current being supplied to the transistor will be infinity, and I cannot see any transistor that can handle infinite current like that.

[audioguru]

Transistor manufacturers make similar transistors have different pins, just to fool the noobies:
A BC547 has pins in the sequence of CBE.
A 2N3904 transistor has them as EBC.
Some little transistors have the middle pin as the collector.
If the pins are wired backwards then the base-emitter junction becomes reverse-biased and will avalanche breakdown like a zener diode at about 6V.

[MP]

uh....yeah.... I am sure they are just doing that to fool the noobies.... ::)


MP