line driver with automatic bias

OPA552?

John

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yeh, not much point in cooking up something with and opamp and a bunch of discretes, if the right opamp that can do it by itself

-Lasse

This is nice and simple.

ftp://jjlarkin.lmi.net/OpampBoost.JPG

The resistor lets the opamp do some of the work at low level, eliminating the deadband. Sort of. No thermal problems at all.

We could have a 500+ post thread about which "class" this is.

I don't understand Ban's circuit.

John

What a pile of crapola. Did you get that from Larkin ?:-) ...Jim Thompson

It is also very new and original.

It won't make much difference if you replace resistor with capacitor. Or eliminate the resistor at all.

But why the conservatives didn't kick out Sara Palin? She spoils everything she touches!

His circuit is an audiofool way of making emitter follower. The opamp actually meant to be LM358, as it pulls down.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

But, it has values ;)

Cheers

Neither do I. How do the output devices' bases get their drive?

Bob

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

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Why the diode?

-- Cheers, James Arthur

Without the diode, the output stage is pulled by resistors only. Diode helps if there is not enough of current.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Sorry, but it has the same number of parts, and try to establish a stable bias current from -25° to 125°. The variation is less than 5%. The distortion at 10kHz 20Vpp 100R load is less than 0.025%. With some

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

Larkin will like it a lot after he has put it in the simulator and compared to his circuit, maybe you should do it too?

The PNPs are upside down.

Tim

-- Deep Friar: a very philosophical monk. Website:

So did you draw the PNPs upside down? Or operate them backwards on purpose?

Grant.

I just asked that too, 'cos it don't make sense otherwise, and then it's nothing new?

Grant.

The bases are connected together, a strange and unusual configuration. Put it in a pspice simulator and see what happens. Ban Apricale, Italy

I thought maybe that was it--slew rate enhancement. Works in both directions too.

That's cute. Ban's is better for crossover distortion though--I think that's what he was after.

-- Cheers, James Arthur