Abstract: An amplifier comprises an amplifier circuit for amplifying an input signal and a supply voltage detector for controlling the operation of the amplifier circuit. The supply voltage detector has hysteresis characteristics as to a first threshold voltage and a second threshold voltage which are different from each other in order to detect the magnitudes of the supply voltage. The amplifying operation of the amplifier circuit is controlled as to the start-up and turn-off operation thereof by an output signal of the supply voltage detector.

Abstract: Two output transistors constituting a push-pull output amplifier circuit are connected in series between a power supply and a grounded point, and an output terminal is disposed at a point where the two output transistors are commonly connected. An operation detector circuit detects the operation of one output transistor. A level detector circuit detects a d-c voltage level at the output terminal. The two output transistors are driven by a drive circuit in a push-pull manner. The output of the operation detector circuit and the output of the level detector circuit control the drive circuit via a control circuit. When the operation detector circuit detected the fact that the operation of one output transistor has deviated beyond a predetermined detection level, the control circuit works to confine the operation of the abovementioned output transistor within a predetermined restriction level via the drive circuit. The power loss in the restriction level is smaller than the power loss in the detection level.

Abstract: A two signal amplifying system is constructed of first and second BTL amplifiers each including a phase splitter and first and second push-pull output circuits. In each of the first and second push-pull output circuits, output transistors are connected between a power source and output terminals, and detectors for detecting the operating states of said transistors are connected with the output transistors constituting the aforementioned first and second push-pull output circuits, respectively. The outputs of those two detectors are fed to a control circuit. The output of the control circuit renders the two output transistors nonconductive in case at least one of the two output transistors deviates from a predetermined operating range.

Abstract: A semiconductor integrated circuit device for an amplifier circuit including a semiconductor substrate in which an audio amplifier circuit is formed in an integrated circuit form, at least one first wire bonding pad which is formed on said semiconductor substrate to ground said audio amplifier circuit, and an externally connecting terminal which is provided being separated away from said semiconductor substrate and which is electrically connected to said first wire bonding pad via a metal wire, wherein the improvement comprises a wire bonding pad for the substrate which is formed on said semiconductor substrate being separated away from said first wire bonding pad, and which grounds said semiconductor substrate, and a metallic connector wire which electrically connects said wire bonding pad for the substrate to said externally connecting terminal.