OT: The flame has been lit, I hope

Here's a simple circuit using 3 resistors and a npn transistor. Notice the load current in R2 varies only 10 percent as the supply voltage is ramped

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snip That's 2 resistors, which is familiar territory. I don't see a way to do it with one. Not unless you scrape some paint off!

NT

I might just have found a way to do it with one. It's crude, but might suffice for some jobs.

Vcc | | R o | | | _| c

The collector now takes a constantish current. Sort of.

NT

and of course to deliver constant i out...

______________ Vcc | | _| e +-----(_) pnp | | c | | R o | _|___________ 0v

NT

Commonly called "suicide bias". ...Jim Thompson

I wish you'd write a book.

That's what my wife keeps saying O:-)

But there's no money in it. ...Jim Thompson

If you're using that method to bias a class A stage to 1/2 Vcc, it would indeed be a gamble. Used as above at low current with low temp rise it isn't.

NT

I don't gamble. ...Jim Thompson

the above circuit isn't a gamble

NT

It's seriously Beta and Vce dependent. ...Jim Thompson

I'll send ya a few bucks if you write a book. And think of the fame and glory. :^)

George H.

Ignoring SWMBO is path fraught with peril.

Get an intern to do most of the slogwork?

--sp

Yes. Lots of modern transistors are binned by beta, giving a limited range there.

Vce is routinely regulated. When it isn't it doesn't normally vary greatly.

Temp also affects it by reducing Vbe. But not a lot. And temp swing can be kept down trivially.

So in short it's inaccurate, but there are many situations where it's near enough.

NT

Beta increases as temperature rises... beta increases make for more IC, makes for more temperature rise... makes for suicide bias.

Vce changes == Early effect, current rises... most serious with no emitter degeneration

Vbe has nothing to do with this "configuration".

Not in anybody's book but yours... you're bloviating outside your league >:-} ...Jim Thompson

I've never been much of one for fame and glory. My policy, at Motorola, was to let the team take the fame and glory... I took the promotions >:-} ...Jim Thompson

I've seen that idea used in cheap transistor radios to bias the IF stages with a single resistor. If the beta is high, you get 2 milliamps, and if the beta is low you get 1 milliamp into the IF transformer. And some of these old radios keep working for 40 years.

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Does the resistor tie directly to Vcc or to the collector of the transistor? ...Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

I think it ties directly to Vcc to avoid the negative feedback. The resistor is around 300K

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