Amplifiers – With semiconductor amplifying device – Including push-pull amplifier
Patent
1986-05-02
1988-03-01
Mullins, James B.
Amplifiers
With semiconductor amplifying device
Including push-pull amplifier
330265, 330266, 330268, 330300, H03F 330
Patent
active
047289031
ABSTRACT:
The disclosed amplifier comprises a MOSFET output stage biased for Class A operation and a bipolar current amplification stage biased for Class C operation. The latter stage is normally cut off, and at low power output levels the entire output signal current is provided by the output stage. Current sensing resistors measure the magnitude of the output current and apply to the base-emitter junctions of the current amplification transistors a bias voltage proportional to the output current. When this current reaches a predetermined magnitude the current amplification stage becomes active so as to provide additional output signal current in parallel with that provided by the output stage. As a result at higher power output levels the output stage sees a load impedance much higher than that of the loudspeaker system and therefore has a flatter load-line which maintains its operating point in the active region. The output stage is thereby maintained conductive and operates in the Class A mode notwithstanding a relatively moderate quiescent current of about one ampere.
REFERENCES:
patent: 3968450 (1976-07-01), Suzuki et al.
patent: 4483016 (1984-11-01), Hochstein et al.
patent: 4531099 (1985-07-01), Nakane
Wen, "Simple Current Booster for Operational Amplifiers", New Electronics, vol. 14, No. 14, Jul. 1981, p. 27.
1984 Databook, vol. 29, Book 2, Mar. 1984, pp III, G30, 33, 34, 147.
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