Amplifiers – With semiconductor amplifying device – Including differential amplifier
Patent
1987-05-11
1988-07-12
LaRoche, Eugene R.
Amplifiers
With semiconductor amplifying device
Including differential amplifier
330266, 330289, H03F 345
Patent
active
047572710
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an amplifier circuit and, in particular, to a circuit comprising an amplifier section, a power supply section and a preamplifier section, all sections working together to provide an amplifier suited for use as a high fidelity audio amplifier.
BACKGROUND ART
Many audio amplifier circuits are known. However, output from such devices typically suffers to a greater or lesser degree from instability in the biasing of the output stages and/or distortion arising from imperfections in the DC power supply for the power amplifier stage.
Further, in many amplifier circuits, either no provision is made for coping with overload conditions (either by way of high amplitude inputs and/or by way of very low impedance between the output(s) and common). Where provision is made, the protection is frequently of the "after the event" type wherein damaging levels of current, voltage or temperature are reached before the protection operates.
It is an object of the present invention to overcome, or substantially ameliorate, the abovementioned disadvantages.
DISCLOSURE OF INVENTION
In one broad form the invention provides. A composite audio amplifier comprising at least one symmetrical, dual polarity audio amplifier power supply and a glass AB audio amplifier circuit, said symmetrical, dual polarity audio amplifier power supply comprising
first positive and negative and second positive and negative unregulated DC inputs;
positive and negative regulated outputs and a common output;
a first and second regulator circuit;
said first regulator circuit including at least one pass transistor having its emitter connected to said first negative unregulated DC input and its collector connected to said common ouput, said second regulator circuit including at least one pass transistor having its emitter connected to said positive unregulated DC input and its collector connected to said common output;
each said pass transistor having a pass resistor connected between the emitter and collector of said pass transistor;
said first regulator circuit deriving a reference signal from said negative regulated output and said second regulator circuit deriving a reference from said positive regulated output;
said first and second regulator circuit deriving power from said positive regulated output and common and said negative regulated output and common respectively;
said class AB audio amplifier circuit comprising in combination
a primary operational amplifier driving complementary power transistor output stages;
bias current for said complementary power transistor output stages including bias current adjustment means to adjust said bias current in response to the temperature of at least one of a power transistor forming part of said complementary power transistor output stages;
the signal output of said primary operational amplifier being fed to complementary symmetric first and second arms of a current shunt network, said current shunt network adapted to shunt base current from said complementary power transistor output stages when said signal output of said primary operational amplifier exceeds a preset maximum threshold and, at the same time, said signal from said power output drops below a preset minimum threshold;
said current shunt network adapted to allow transient overload conditions.
In a preferred embodiment of the invention the amplifier differs from the conventional amplifier by having an efficient circuit for preventing damage to the output transistors and loud speakers by sensing overloads and short circuits at its output and by stabilising the effects of temperature. The result is that bias can be increased to a level which would be damaging to a conventional amplifier thus producing exceptionally high fidelity performance where the amplifier is used as an audio amplifier.
In particular, in a preferred embodiment, extremely high fidelity has been achieved by an unusually high speed capability, linearity and absence of cross-over distortion which had been achieved by retaining functi
REFERENCES:
patent: 4638260 (1987-01-01), Hanley
John Dumergue Charters
LaRoche Eugene R.
Mottola Steven J.
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