Composite bridge amplifier with output overload and thermal prot

Details Composite bridge amplifier with output overload and thermal prot Composite bridge amplifier with output overload and thermal prot

1994-11-22

1996-04-23

Mullins, James B.

Amplifiers

Wheatstone bridge with amplifier in at least one arm

330 10, 330251, 330289, 330297, 330298, H03F 3217

Patent

active

055107532

ABSTRACT:
A composite bridge amplifier has four output transistors in a bridge configuration. The transistor control terminals (gates or bases) are controlled by an input signal which is amplified in a phase splitter and voltage gain stage. The output terminals of the transistors receive a power signal which varies with the input signal at a level sufficient to maintain headroom above the output signal but to reduce power dissipation in the transistors. The power signal is produced by a switch connected between a floating power supply and a filter and operated at e.g. 200 kHz. The switch is operated by a pulse width modulated (pwm) signal derived from the absolute value of the input signal. A proportional integral controller is coupled between the filter output and the pulse width modulator for closed loop feedback. The output is aligned with the input signal by a phase shifter connected to the controller. Since there is no time delay in the input signal (i.e. audio) path, high performance is achieved at reduced cost. For improved high frequency performance, the amplifier includes a peak detector circuit for tracking a high frequency input signal and compensating the pwm signal. The amplifier also features thermal overload protection and output current overload protection circuits which protect the output stage by reducing the headroom. Because the protection circuits do not "clip" the output signal, the effect to the listener is minimized.

REFERENCES:
patent: 3829788 (1974-08-01), Ford
patent: 4016501 (1977-04-01), Jasinski et al.
patent: 4949050 (1990-08-01), Swanson
patent: 5075634 (1991-12-01), French

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