Disclosed is a Class A power amplifier circuit which includes means for controlling the quiescent bias current of the output devices of the amplifier and providing absolute overload and short circuit protection without the need of extra protective devices of any kind. The circuit includes a driver stage which amplifies an input signal and provides two outputs which are out of phase with respect to each other by 180.degree.. One output of the driver stage provides a drive signal to the control input of a first output device, while the other output of the driver stage provides a drive signal to the control input of a second output device. Power is provided to the driver stage by a standard grounded center-tapped power supply. A pair of independent floating power supplies are cross-connected between the two output devices so that the supply terminal of each output device is connected to one terminal of one of the power supplies, while the output terminal of each of the output devices is connected to the opposite phase terminal of the opposite power supply. A resistor is connected between the output terminal of each of the output devices and one terminal of the power supply which powers the driver stages. The load is connected between output terminals of the output devices. The circuit arrangement provides control of the value of the quiescent control input current of each of the output devices which in turn controls the quiescent value of the bias currents of each of the output devices, thus resulting in an amplifier of greatly improved thermal stability.
A class A bridge topology for audio amplifiers configured to operate in constant current mode, comprising power stages (3,4,5,6) supplied by supplies (8,9) and driven to equal amplitude opposite phase output signals applied across a load (7). Symmetrical current conditions are placed on said power stages to achieve a cancellation of supply currents during signal application to the load. Supplies are current limited to afford non-intrusive protection against overstress.
A wide bandwith video amplifier circuit with a high output DC voltage bias and which is capable of high tracking linearity. The video amplifier circuit comprises an AC pre-amplifier, a DC restorer amplifier stage and a DC output stage. The DC restorer amplifier stage and the output stage operate from a first DC power supply which is floating such that the output stage can be biased at a desired D.C. voltage, relative to a floating ground. A first power supply is used to provide the necessary power to the amplifier circuits, DC restorer amplifier and the output stage. A second power supply provides a DC bias voltage to the output stage and DC restorer stage which is additive to the DC level of the amplifier circuit set within a floating DC power supply. This DC bias voltage can be altered relative to a true 0 volt ground level, thus allowing the setting of the DC bias of the output stage at a required level relative to the true ground potential.
The present invention is a circuit for use as a preamplifier or amplifier. The circuit has first and second input terminals that are configured to receive first and second balanced input signals. The circuit also includes first and second active devices that control output signals. Each of the active devices have a source, a control, and an output. In one embodiment, the control of the first active device is coupled to the first input terminal. The control of the second active device is coupled to the second input terminal. The circuit further includes first and second output terminals at which output signals are provided. The first and second output terminals are coupled to the first and second active devices. The circuit includes an coupler that couples a floating power supply to the first and second output terminals, and to the first and second active devices.
A high fidelity audio amplifier is provided having a solid-state floating bridge output stage and a preceding solid-state driver stage configured to operate with negligible voltage fluctuations and minimal current fluctuations, resulting in reduced driver stage distortion, freedom from driver stage clipping, and high and linear impedance at the driver input terminals, without significant increase in circuit complexity. The voltage gain and current gain sections of the amplifier form self-contained units which may be separately housed and remotely operated to enhance utility and isolate sensitive voltage gain circuits from the radiated electrical noise and heat of the output stage.
An improved Class BD amplifier provides an amplified output signal by pulse width modulation techniques by sampling a carrier wave, usually a triangular or saw tooth waveform, according to an input signal to be amplified, as in a conventional class D amplifier. The resulting sampling waveform controls the connectivity of the potential supplies 34, 36 to the power rails 14, 18 via the first switch 12 so that a first potential and a second potential are alternately supplied to the first power rail 14 and so that a third potential and fourth potential are alternately supplied to the second power rail 18. As shown in FIG. 8, the first potential is positive, the second and third potentials are at ground, and the fourth potential is negative. In addition, a constant potential difference is maintained between the first and second power rails 14, 18. The power rails are alternately connected to a Class AD output stage 26 by another switch 30, the connectivity of which is controlled by a second sampling waveform, PWM.sub.2. This second sampling waveform PWM.sub.2 may also be derived by sampling a triangular or saw tooth carrier wave by the input signal.
