Abstract: An amplifier circuit including two general purpose operational amplifiers is disclosed. The output terminals of first and second operational amplifiers are connected via first and second resistors in series. A connection point between the first and second resistors is connected to an output terminal and is also connected to an inverting input terminal of the first operational amplifier via a feedback loop. Thus, the first and second operational amplifiers work as class-A amplifier, so that the crossover distortion is prevented from being generated. An input signal is inputted to a non-inverting input terminal of the first operational amplifier wherein the input signal is amplified. The amplified input signal is added with a dc bias voltage and is supplied to a non-inverting input terminal of the second operational amplifier. The output voltage of the first operational amplifier varies in a positive voltage area, and the output voltage of the second operational amplifier varies in a negative voltage area.

Abstract: An output transistor protection circuit in a power amplifier comprises a limiter circuit which limits a collector power dissipation of the output transistors to a predetermined magnitude in accordance with an output voltage level of the amplifier and a current level of the output transistors. For sure limitation operation with a low cost construction, and without destruction of signal waveform, limitation characteristics of the limiter circuit is varied in accordance with detection results of an output voltage level detection circuit which detects whether the output voltage level is smaller than a predetermined magnitude, and a clipping condition detection circuit which detects whether an output stage of the amplifier is clipped.

Abstract: A power amplifier with power supply switching is arranged so that large positive and negative power supply voltages are supplied to collectors of second and fourth transistors via first and third transistors, respectively. Small positive and negative power supply voltages are supplied to collectors of the second and fourth transistors, respectively, and an input signal of the amplifier is amplified by the second and fourth transistors to supply an output of the amplifier to a load, wherein to a base of the first transistor is selectively applied either a divided voltage between a positive constant voltage greater than the small positive power supply voltage and the voltage of the input signal or a voltage which is a sum of the voltage of the input signal and a positive constant voltage.

Abstract: In a power supply changeover type amplifier arranged so that the voltages supplied from a plurality of power supplies to a power amplifying circuit are varied in accordance with the magnitude of level of an input signal which is to be amplified, arrangement is provided so that the plurality of power supplies having mutually equal output voltages are connected together in parallel and/or in series in accordance with the magnitude of the level of the input signal, and that the voltages resulting from the connection are supplied to the power amplifying circuit, to thereby enhance power efficiency of the amplifier and materialize its power supply section having a compact size and a light weight.

Abstract: In a power supply circuit designed so that an AC voltage is applied to the primary side of a transformer, and that the voltage derived on the secondary side thereof is rectified and smoothed, arrangement is provided that the AC voltage applied to the primary side is subjected to switching at least twice in each half cycle thereof to insure that the current which flows on the primary side is timewisely divided, whereby the peak value of the current flowing on the primary side of the transformer is suppressed to a small level. Thus, it is possible to realize a substantial reduction of noises as a result of minimized dI/dt and current value and also to realize a substantial reduction of power loss as a result of minimized current value.

Abstract: A direct-coupled DC amplification circuit effects amplification over all the amplification stages using a ground potential as the reference voltage, and yet supplies a load with voltages in both positive and negative directions. In one preferred embodiment, a second or subsequent amplification stage including a phase compensating element has an amplification element in the form of cascode-connected complementary transistors connected to positive and negative power input terminals via first and second constant current circuits, respectively, and the set current of the first constant current circuit is set to be twice greater than that of the second constant current circuit.

Abstract: A constant-voltage power source device for a highly accurate electric circuit, connected to an A.C. power source, capable of minimizing size of the current loop, making the ground line current constant even when the load current varies, and having a high noise elimination ratio as well as a low output impedance.The device comprises a constant-current circuit connected in series with the load, and in parallel therewith a constant-voltage circuit including a control amplifier which controls the current flowing therethrough so that sum of this current and the output current of the device supplied to the load equals to the output current of the constant-current circuit.