| 主权项 |
1. A power supply system comprising:
a switching power supply comprising a controller, the switching power supply being configured to generate a predetermined DC voltage by rectifying and smoothing an AC voltage of an AC power supply; a control device configured to switch the switching power supply between a normal mode in which the switching power supply generates the predetermined DC voltage, and a power saving mode in which the switching power supply stops generating the predetermined DC voltage; and a low-capacity power supply circuit configured to supply electric power to the control device in the power saving mode, the low-capacity power supply circuit including:
a first capacitor including a first electrode connected to one end of the AC power supply, and a second electrode;a second capacitor including a first electrode connected to the other end of the AC power supply, and a second electrode;a rectifier circuit that is electrically connected between the second electrode of the first capacitor and the second electrode of the second capacitor, and is configured to:
rectify the AC voltage applied between the first electrode of the first capacitor and the first electrode of the second capacitor; andsupply a rectified current;a zero-crossing detecting circuit that is connected to a current path at a rear stage of the rectifier circuit, and is configured to:
detect zero-crossing points of the AC power supply on the basis of the rectified current received from the rectifier circuit; andgenerate a signal based on the detected zero-crossing points; anda DC-to-DC converter that is connected to the current path at the rear stage of the rectifier circuit, and is configured to generate a predetermined DC voltage by converting a DC voltage received from the rectifier circuit; wherein the zero-crossing detecting circuit includes a transistor and the rectifier circuit includes first and second output terminals, wherein the first output terminal of the rectifier circuit, a third capacitor and a base of the transistor are connected in series, and the third capacitor is provided between the first output terminal of the rectifier circuit and the base of the transistor, wherein the second output terminal of the rectifier circuit and the emitter of the transistor are both connected to a reference potential line, and the collector of the transistor is connected to, via a pull-up resistor, the switching power supply, and wherein a current path is formed from the first output terminal of the rectifier circuit to the reference potential line through the third capacitor and a resistor; the third capacitor is connected to the rectifier circuit, and smooths the rectified AC voltage so as to generate a smooth voltage which is supplied to an input terminal of the DC-to-DC converter; the base of the transistor is connected between the third capacitor and the resistor to the current path, and the transistor acts as a switching transistor which operates according to a base current generated by the rectified current flowing in the current path. |
