Various Transistors Tested for Ic and Vce(sat)

Make a little converter board the reroutes the pins for you so you don't have to rewire the circuit every time you go from cbe to bce. or add a separate socket :)

Pffbbt.. just bend the pins around so they swap..don't short them :)

Tim

-- "That's for the courts to decide." - Homer Simpson Website @

heh, heh. Try plbht. That's how I heard an IT mgr spelling it. I think he got it from the educational section (cartoons.)

I never did like bending leads around like that.

Can you write a technical description of how that circuit works?

Pretty sad "design".

...Jim Thompson

Please collect data as follows...

Measure beta of each device at the current you observed, with VCE=0.7

Also record duty cycle for each device.

...Jim Thompson

You've sure got that right. What the hell kind of circuit is that? No wonder the L.E.D. overheats!

Yep, You can get upwards of 500mA peak into the LED with the "right" transistor.

I was just trying to introduce the concept of "analysis" into circuits of this sort.

Watson has hung his hat on VCE(sat) and that's only a small portion of the variability he's observing.

I am certain that Watson, and most lurkers here, *cannot* analyze (i.e. predict performance in advance of building) this circuit.

Fred Bloggs: Please hold your tongue so that I can incite some thinking... if you simply spit out the answer all my attempts at teaching people to think will be lost.

...Jim Thompson

In article , snipped-for-privacy@charter.net mentioned...

Like to see you try that with toobs!! ;-P

In article , snipped-for-privacy@invalid.invalid mentioned...

Well, yeah - hey it's simple. The URL for the whole project, including a technical explanation of circuit, is at

If Electronic Design isn't the authority, then who else can you trust? ;-)

In article , snipped-for-privacy@invalid.invalid mentioned...

Is this a homework exercise?

As is much of life ;-)

In article , snipped-for-privacy@no.spam.us mentioned...

Overheat? With a 2N3904? How? The 2N3904 might, since it's such a wimp.

Yes ;-)

...Jim Thompson

In article , snipped-for-privacy@invalid.invalid mentioned...

I don't have a SPICE prog. Like Steve Ciarcia says, my favorite programming language is solder.

Hey the thing's sitting there, working. For the inductor, I used a Mouser #580-22R104.

Electronic Design an authority? ROTFLMAO!

Particularly got a kick out of "There's a limitation..." ;-)

That's nothing more than an *inaccurate* hand-waving.

The purpose of asking for the data-taking was to cause your mind to do a little correlation and then some further thought ;-)

For instance... what *is* saturation and what determines when a transistor will come out of saturation?

...Jim Thompson

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Jim Thompson wrote

"Yep, You can get upwards of 500mA peak into the LED with the "right" transistor".

No mention was made of the 2N3904...just the "right" (or wrong depending upon your point of view) transistor.

(1) I didn't have in mind using Spice. Use pencil and paper. Remember that stuff?

(2) What is the definition of "working"... as you *predicted* before building it, or that it just happens to light the LED ?:-)

...Jim Thompson

Will a slide rule do? ;-)

I think the definition of this particular circuit working is when you see a plume of smoke rising from the L.E.D. and hear it screaming for mercy :-)

Sure! I used to teach a course in how to use a slide rule. I still have my K&E in its green "leather" case with a belt clip ;-) Also a

It *does* lack of predictability, but I suspect that's fixable.

I can eyeball the thing and see how it works, but it'll probably be tomorrow before I can put pencil-to-paper... I'm madly scrambling to finish a design review report.

...Jim Thompson