line driver with automatic bias

[Tauno Voipio]

Reversing the Collector and Emitter will guarantee that it will not or
may not always work.

Reversing emitter and collector for a small signal
silicon transistor will still work, but:

- the 'collector' to base junction will zener at 6 to 9 V,
- the beta may be less than 1,
- the saturation voltage is tiny.

 

[JosephKK]

This one is simpler and better in all ways:

http://www.abvolt.com/misc/line_drv.jpg


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Looks kinda like a lame rebuild of an LH0002C

 

[JosephKK]

It's an old input bias current compensation circuit gone awry by
amateur application :-(

...Jim Thompson

I wish it were that good, the PNPs are upsidedown.

 

[JosephKK]

The resistor onthe upper left drives 1mA into the emitter of the PNP, from
which most will be taken by the collector, only 1/beta will flow out of the
base into the base of the NPN O/P transistor. This causes the same quiescent
current flowing in the output pair.
Temperature variation is minimal, since we do not have a bias voltage but
current drive, and the first transistor adjusts its base current
accordingly.

ciao Ban

Build it _exactly_ as drawn, measure it and then tell us about it.

 

[JosephKK]

It's one of those PhD circuits... Piled higher and Deeper... nice
theory/simulation (†), but crap in practice

(†) Which would catch the issues if the guy in the cockpit had any
clue as to what to test for ;-)

...Jim Thompson

That was uncharastically kind. The circuit is fubar. It may even
work but it is evil and wrong.

 

[JosephKK]

Sonuvagun! I usually catch hell for being blunt.

Burr-Brown used to do something like that to compensate input stage
bias current in their bipolar OpAmps.

...Jim Thompson

I had alread seen plenty of that when they still published decent
equivalent schematics. Early bias cancellation was elegant.