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Ok, this is a question that is not so battery-charger specific, but is obviously related.

So here's a circuit fragment:

18V +----+--------__^------/\/\/-----------+ | 2n3055| 0R5 | | | 5W / | | \ 5R10W | | / |_______|> \ | |_ 2n2906 | | | | | | | | | | +------__^ 2n2222 | | | / | 1M \ | / | \ | | | | | \ SW | \ | | | 5V +-----------+ | | GND +-----------+-------------------------+

So this circuit shows ~38mA going in to the base of the 2n3055, and ~13.9V across the 5 ohm resistor. It gets warm quickly.

If I change the 2n3055 for a TIP147 (PNP, beta 1k) and make the obvious changes to the 2n2906 to make it work, there is ~80mA current at the base of the TIP147, and ~14.1V across the 10W resistor.

WTF, over?

Needless to say I am happy that my $14.00 DVM has a transistor tester, because with 10k feeding the 2n2222 the 2n2906 doesn't last very long with a TIP147 in-circuit. Of course, in that configuration the base of a 2n3055 still shows 38mA. These results suggest that the base-emitter current of the 2n3055 cannot go any higher without a larger power supply, but that is supposition that the 2n3055 somehow limits the base current to some proportionate ratio to the collector- emitter current available to it. Is that in any way a reasonable explanation for what is occurring here?

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.
Reply to
Uncle Steve
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"Uncle Steve"

** Yep.

The B-E current is related to the C-E current by a ratio called "beta" or "Hfe". Beta is not however a fixed number, it varies over the range of possible collector currents.

For a 2N3055 over the range of 0.1 amps to 3 amps, the number is fairly constant at about 50 to 100 - depending on the particular device. The value falls at lower and higher currents PLUS when the C-E voltage is very low.

See figure 3 " DC Current Gain, 2N3055 NPN "

formatting link

All the graphs are worth study, as this is how most power transistors behave.

... Phil

Reply to
Phil Allison

Draw it up real purty, so you can tell PNP's from NPN's and can see that current can only flow OUT of the NPN emitter and INTO a PNP emitter... and DO THE MATH ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

OK. First, the drawing came through mangled. I hope I reconstituted it correctly.

Second, the way you have it drawn, the 2N2222 isn't going to act like a transistor. If you _really_ did it as drawn, the BE junction of the

2N2222 will act like a zener diode at around 6V, because that's just what little transistors do when you challenge their BE junctions with too much voltage.

Third, you've drawn the 2N2906 as an NPN, but my references says it's a PNP.

Frankly, I don't see how this circuit can do _anything_, which leads me to believe that either it is not drawn as built, or there's some more zener breakdown or other oddball things happening.

Like JT said: you've got to put current _into_ the base of an NPN, and pull current _out_ of the base of a PNP for them to act properly. You don't seem to be making that happen.

--
Tim Wescott 
Control system and signal processing consulting 
www.wescottdesign.com
Reply to
Tim Wescott

if you want to use a microcontroller you have to design the low side switch part so that current flows out of the 5V node, not into it.

so dont do this:

do either this

| |/ 5V--[10K]--| |>| | | \ sw \ | ------------+----------

or this: sw | / |/ 5V--/ --[10K]--| |>| | | ------------+-------

--
?? 100% natural
Reply to
Jasen Betts

If you want to use a microcontroller you have to design the low side switch part so that current flows out of the 5V node, not into it.

so dont do this:

do either this

| |/ 5V--[10K]--| |>| | | \ sw \ | ------------+----------

or this: sw | / |/ 5V--/ --[10K]--| |>| | | ------------+-------

if you wat to be sure put in a diode from the switch output to +5 , a microcontroller will have that internally. it also has a diode from ground.

like this: | | |/ 5V--+--[10K]--| | |>| | | `----||-----+ | | | \ sw | \ | | +-----------+----------

or this: | | / |/ 5V-+-/ -+-[10K]--| | | |>| `-|

Reply to
Jasen Betts

I see the significance of these curves a little better now, and it's probably somewhat unreasonable to compare a BJT with a Darlington. The interesting thing is that the behaviour of the BJT seems to be more 'reasonable' in this application since it protects the previous stage.

The next step for me is to figure out how to predict these factors to reduce the amount of fooling around I am still doing. Nevertheless, there is nothing like making measurements to show what is in fact going on with these devices.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.
Reply to
Uncle Steve

Sorry, I was tired and really mangled the schematic. Fixed above.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.
Reply to
Uncle Steve

"Uncle Steve"

** Give this man a Kewpie doll.

... Phil

Reply to
Phil Allison

No, this is actually it:

18V +----+--------__^------/\/\/--------+ | 2n3055| 0R5 | | | 5W / | | \ 5R10W | | / | | \ +------__v 2n2906 | | | | | 2n2222 +---| | | |>----+ | | | | / | | 1M \ | | / | | \ | | | | | | | | \ SW | | \ | | | | | 5V +-----+ | | | | GND +---------------+------------------+

My brain isn't trained to recognize the symbols and circuits with any fluency yet, so when I did the original drawing while tired, it didn't register. Apologies for the confusion.

When I make silly errors like that when writing code it's also vastly amusing.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.
Reply to
Uncle Steve

When I actually hook this up to a microcontroller the 5V will be the output from the pin designated for PWM, assuming I stick with that strategy. As I said earlier, the switch is there to simulate a microcontroller.

Not sure what the purpose of the second diode is there. Doesn't look like it can do much of anything.

It's hard to say. When I was using a motor as a load there were wierd things happening all over the place, but I was also making stupid mistakes and damaging small signal transistors in non-obvious ways.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.
Reply to
Uncle Steve

I've always wanted a Kewpie doll.

It's interesting that all of the literature and web-pages I've read so far have failed to impart an accurate sense of what these things do. I don't know whether that is because the learning curve is so steep, or whether the terminology is truly confusing to the uninitiated. I think it might be easier to understand electronics if circuit diagrams represented electron flow and electron charge potential more obviously. After all it's the electrons moving around that gets work done, correct?

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.
Reply to
Uncle Steve 

--
Version 4 
SHEET 1 880 708 
WIRE -16 0 -192 0 
WIRE 96 0 -16 0 
WIRE 176 0 96 0 
WIRE 320 0 272 0 
WIRE -16 64 -16 0 
WIRE 96 112 96 0 
WIRE 224 112 224 64 
WIRE 224 112 192 112 
WIRE -16 208 -16 144 
WIRE 144 208 144 176 
WIRE 144 208 -16 208 
WIRE 144 240 144 208 
WIRE 320 272 320 0 
WIRE 144 352 144 320 
WIRE -32 400 -80 400 
WIRE 80 400 48 400 
WIRE -192 480 -192 0 
WIRE -80 480 -80 400 
WIRE -192 624 -192 560 
WIRE -80 624 -80 560 
WIRE -80 624 -192 624 
WIRE 144 624 144 448 
WIRE 144 624 -80 624 
WIRE 320 624 320 352 
WIRE 320 624 144 624 
WIRE -192 688 -192 624 
FLAG -192 688 0 
SYMBOL npn 176 64 R270 
WINDOW 0 68 29 VRight 2 
WINDOW 3 99 3 VRight 2 
SYMATTR InstName Q1 
SYMATTR Value 2N3055 
SYMBOL npn 80 352 R0 
SYMATTR InstName Q3 
SYMATTR Value 2N2222 
SYMBOL res 304 256 R0 
SYMATTR InstName R1 
SYMATTR Value 5.5 
SYMBOL voltage -192 464 R0 
WINDOW 123 0 0 Left 2 
WINDOW 39 0 0 Left 2 
SYMATTR InstName V1 
SYMATTR Value 18 
SYMBOL voltage -80 464 R0 
WINDOW 3 24 96 Invisible 2 
WINDOW 123 0 0 Left 2 
WINDOW 39 0 0 Left 2 
SYMATTR InstName V2 
SYMATTR Value PULSE(0 5 0 100n 100n 1 2) 
SYMBOL res 64 384 R90 
WINDOW 0 0 56 VBottom 2 
WINDOW 3 32 56 VTop 2 
SYMATTR InstName R3 
SYMATTR Value 2.7k 
SYMBOL pnp 192 176 M270 
WINDOW 0 61 61 VLeft 2 
WINDOW 3 92 86 VLeft 2 
SYMATTR InstName Q2 
SYMATTR Value 2N2907 
SYMBOL res -32 48 R0 
SYMATTR InstName R2 
SYMATTR Value 10k 
SYMBOL res 128 224 R0 
SYMATTR InstName R4 
SYMATTR Value 1k 
TEXT -176 656 Left 2 !.tran 5
Reply to
John Fields

PNP collector must be more negative than its emitter... swap emitter and collector on the 2N2906.

But you're still in "fry" land :-(

WHAT is the OBJECT of your endeavor? Trickle charging a back-up battery? ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

[snip]

Nope, that is your main conceptual error.

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

I wish I could run that fancy ASCII schematic CAD tool, but I don't use Windows.

I wouldn't characterize 3A as a trickle, but in essence I hope to end up with a battery charger that will charge the battery while it is under a moderate 20W+ load. I have bit-banged serial out on the microcontroller, so it will log status to the load device that way, and inform it when mains power fails.

It is a learning exercise, but I hope to end up with something vaguely resembling a UPS when all is said and done.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.
Reply to
Uncle Steve

Except in PNPs. ;)

Seriously, once current starts to be an intuitive concept for you, you'll rarely need to think about electrons at all.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs 

--
No. 

In reality it's the base-to-emitter current which controls the 
collector-to-emitter current. 

The ratio of Ice to Ibe is called 'beta' or 'Hfe' and describes the 
current gain of the device. 

From the curves you have, you can see that Hfe varies widely with 
collector current and temperature, and also from device to device.
Reply to
John Fields

Because the TIP147 is PNP and operates completely differently. Is the issue here that the 3055 is 'fully on' with 5 uA driving the

2n2222?

Perhaps my frustration with arrangements other than the Sziklai Pair is due to an irrational desire to decouple the 5v circuit from the 18V section as much as possible. Other than in a darlington arrangement, I am still having trouble making 2 2n2222 stages do what I want and the frustration of things not working as I think they should is really annoying.

But at pennies per transistor at least it's not expensive to fiddle.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.
Reply to
Uncle Steve 

--
You might try changing your format. 

Here's an example; it's the ASCIImatic for the LTspice circuit list I 
posted for you earlier: (View using a fixed-pitch font.) 

                              
+18V-----------+-----+-C   E---------+ 
               |     |   B 2N3055    | 
               |     |   |           | 
             [10k]   E   C           | 
               |       B 2N2907      | 
               |       |             | 
               +-------+           [5.5] 
               |                     | 
              [1K]                   | 
               |                     | 
               C                     | 
IO>--[2.7K]--B  2N2222               | 
               E                     | 
               |                     | 
GND>-----------+---------------------+
Reply to
John Fields

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