Constant voltage circuit and analog electronic clock
There are provided a constant voltage circuit that outputs a stable constant voltage for an analog electronic clock, and an analog electronic clock featuring low current consumption and prolonged battery life. The constant voltage circuit has a first voltage holding circuit connected between the gate of an output transistor and an output terminal and a second voltage holding circuit connected between the gate of the output transistor and a ground terminal, and carries out control such that the second voltage holding circuit is enabled when the motor is operated.
1. A constant voltage circuit, the operation of which consumes less current by performing an intermittent operation at a predetermined interval and which outputs a constant voltage to an output terminal, the constant voltage circuit comprising:
an output transistor connected to the output terminal;
a differential amplifier circuit which controls a gate of the output transistor such that a voltage of the output terminal becomes a constant voltage;
a first switch circuit connected between the differential amplifier circuit and the gate of the output transistor;
a first holding circuit connected between the gate of the output transistor and the output terminal through a second switch circuit; and
a second holding circuit connected between the gate of the output transistor and a power supply terminal through a third switch circuit,
wherein the constant voltage circuit has:
a first operation mode in which the differential amplifier circuit and the first switch circuit are intermittently operated by a first control signal, and the second switch circuit is turned on and the third switch circuit is turned off by a second control signal; and
a second operation mode in which the differential amplifier circuit and the first switch circuit are turned on by the first control signal, and the second switch circuit is turned off and the third switch circuit is turned on by the second control signal.
2. The constant voltage circuit according to claim 1 , comprising:
a precharge circuit which sets the second holding circuit to a voltage of the gate of the output transistor while the third switch circuit is off.
3. The constant voltage circuit according to claim 2 ,
wherein the precharge circuit is constituted of a voltage follower circuit which has an input terminal thereof connected to the gate of the output transistor and an output terminal thereof connected to the second holding circuit through a fourth switch circuit.
4. An analog electronic clock comprising:
a semiconductor device having an oscillation circuit to which power is supplied from the constant voltage circuit according to claim 1 ; and
a motor driven by an output signal of the semiconductor device.