Abstract: A voltage detection circuit of the invention is composed of the minimum needed number of circuit elements and that permits the temperature characteristic of the reference level for voltage detection to be set arbitrarily. The voltage detection circuit has a first transistor and a second transistor that have the emitters thereof connected together to form a differential pair, a voltage division circuit that divides the input voltage into a first division voltage and a second division voltage, that is connected directly to the base of the first transistor to apply the first division voltage thereto, and that is connected directly to the base of the second transistor to apply the second division voltage thereto, and a resistor that has one end thereof connected to the base of the second transistor and that has the other end thereof connected to the emitter of the second transistor. Whether the input voltage is equal to a predetermined level or not is checked based on the output from the differential pair.

Abstract: Conventionally, a voltage detection circuit that is so configured as to make the temperature coefficient of a predetermined level used as the reference level for voltage detection equal to zero is not composed of the minimum needed circuit elements. The voltage detection circuit of the invention is composed of the minimum needed number of circuit elements and that permits the temperature characteristic of the reference level for voltage detection to be set arbitrarily.

Abstract: A power supply device has a soft starting circuit 12, which is composed of a transistor Tr9 having its emitter connected to the emitter of a transistor Tr1 of which the base serves as a non-inverting input terminal of a comparator 11 and having its collector grounded, a clamp circuit 10 connected between the base of the transistor Tr1 and the base of the transistor Tr9, a constant-current source 7 receiving a supply voltage Vcc through a switch 2, a capacitor Cs having one end connected to the base of the transistor Tr9 and having the other end grounded, a switch 9 connected to the capacitor Cs, having its contact “c” connected to the constant-current source 7, and having its contact “d” connected to a discharge circuit 8, and the discharge circuit 8.

Abstract: A power supply device that feeds electric power to an output terminal that is to be connected to a load has first and second PNP-type transistors having their emitters connected to a supplied power line. The collector of the first transistor is connected to the output terminal, and is connected also through two serially connected resistors to ground. An operational amplifier controls the first and second transistors in such a way that the voltage at the node between the two serially connected resistors is kept equal to a setting voltage. To achieve this, a control current is fed to the bases of the first and second transistors. In accordance with the collector current of the second transistor, a limiter circuit limits the output current of the first transistor. The limiter circuit controls the first transistor through the operational amplifier. Between the collectors of the first and second transistors, a capacitor is connected.