Switching power supply with detection of the AC input voltage

摘要

A switching power supply includes a rectifying unit configured to rectify an input alternating voltage, a storage unit configured to smooth the voltage rectified by the rectifying unit and store as a DC voltage, a pulse signal generation unit configured to generate a pulse signal from the DC voltage stored in the storage unit, and a detection unit configured to detect that a commercial alternating current power supply has been turned off based on the pulse signal generated by the pulse signal generation unit.

主权项

1. A switching power supply comprising:
a transformer provided with a primary winding and a secondary winding; a secondary side-detection unit connected to the secondary winding of the transformer, configured to output a first pulse signal in a state that an alternating voltage is input to the transformer; and a primary side-detection unit connected to the primary winding of the transformer, configured to output a second pulse signal according to the first pulse signal; wherein the primary side-detection unit comprises:
two resistive elements configured to divide an alternating voltage input to the primary winding of the transformer;a rectifying unit configured to rectify a voltage divided by the two resistive elements;a capacitor configured to store the voltage rectified by the rectifying unit; anda pulse signal output unit connected to the rectifying unit and the capacitor, configured to output the second pulse signal by receiving the first pulse signal and according to a voltage stored in the capacitor being thereby supplied,wherein, in a case where the alternating voltage is not input, a voltage of the capacitor of the primary side-detection unit is lowered, and the pulse signal output unit thereby stops outputting the second pulse signal.