JLH10W with current regulator

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I took a break from testing the recent JLH-inspired 16W design (that is still a priority, but I'm time limited at the moment) with this sudden insipiration "thought process" idea to automatically regulate the quiescent current in JLH10W amplifier.
The idea is to develop two monitoring signals that are at the same DC level (at least approximately) but driven from the output transistors so that they are oppositely phased. Then, an averaging circuit combines the two. This is one side of a diff pair, the other side is referenced to a DC voltage which will then set the current in the monitor devices and hence the output transistors.
As mentioned it is only an idea. Not tested, but a quick simulation shows it works (very limited, I would have to say this is experimental).
The lower output transistor current is monitored across a 1 ohm emitter resistor. That is double buffered with an emitter follower and a unity gain level shifter to send the signal to the top rail. The upper output transistor is monitored similarly, though perhaps it does not need to be, just to keep things symmetrical, but as it only needs voltage buffering the two transistors are both just emitter followers.
There are some limitations. First, the voltage on the reference side of the diff pair needs to be accurately set. That is no different really from any analogue based design, but does mean it probably needs separately stabilising from the power rail.
The diff pair operate at a high current and consequently the "long tail" resistor is a bit short. THerefore the degree of control is not likely to be particularly great. Thirdly, a wide range of gains of transistor in the output stages could swing the currents in the diff pair around a lot and that would have up to 100mV variation (10% in the 1 ohm resistor) or thereabouts.
Lastly, the additional 1 ohm resistors means increasing the power supply voltage (and heat dissipation) which is a bit of a downside.

I have posted this simply as an idea.
This is on the "to be tested" list now, but no doubt there will be some comments.
 

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