I'm looking at the equivalent schematic for the BA5406 IC power amp here on page 2:
Pin 3 is a boostrap input, I believe to increase the compliance of the current mirror loads and therefore the positive going saturation voltage of the upper Darlington pair, by connecting it via a capacitor to the output. But I don't think it's really internally connected to Vcc...Connecting the output through a capacitor to Vcc would be kind of dumb, right?
Yeah, too dumb.
Someone dropped extra blob there by accident. You can tell by viewing similar devices from others, perhaps same manuf?
Grant.
Thanks for the confirmation of what I suspected. I had to puzzle a bit over how the supposedly class AB output stage on this circuit worked; I came to the realization that it could only work in an IC where the bias
-setting diodes are diode connected transistors, with everything basically matched and you know what the differences in Vbe are going to be for different diode/transistor currents. In that way I guess they're able to get a class AB output without using the traditional method of a Vbe multiplier and emitter resistors on the output transistors.
The bootstrap circuit is a pretty clever way of increasing the available output power at low voltages.
Audio people love to use potentiometers backwards. They do a lot of other stupid stuff, too.
I think that, once people put in the effort to build their own audio amps, they like the sound, no matter how bad it actually is.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
That must have been English -> Some Other Language -> English which would explain 'left' = 'not here'.
Although I suspect Jim T (and most US contributors) would associate 'left' with 'not here'.
Cheers
-- Syd
It's just current summing. ...Jim Thompson
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