Patent ID: 9257909
Filing Date: 2016-02-09
CPC Classification: H02M

Claim Text:
1. A switching power supply comprising: a main body of the switching power supply that performs switching operation of a DC power using a semiconductor switching element ON/OFF-driven at a power supply frequency fs and rectifying and smoothing operation of the switched power to supply a DC voltage to electronic devices including an AM radio receiver; a receiving frequency detecting means that detects a receiving frequency fc of an AM radio broadcast; a power supply frequency detecting means that detects power supply frequency fs of ON/OFF-driving the semiconductor switching element; a higher harmonic detecting means that determines an order n, n a natural number, of a higher harmonic component near the receiving frequency fc of the AM radio broadcast, the higher harmonic being a power supply higher harmonic generated with switching operation of the semiconductor switching element, based on a fundamental power supply frequency fso of ON/OFF-driving the semiconductor switching element; a frequency judging means that judges whether the higher harmonic component of the order n that is determined by the higher harmonic detecting means is higher or lower than the receiving frequency fc of the AM radio broadcast and output a frequency judgment result; a power supply frequency width determining means that determines, according to the frequency judgment result, an upper limit value fs-max and a lower limit value fs-min for a power supply frequency fs that does not interfere with the receiving frequency fc of the AM radio broadcast from values of the fundamental power supply frequency fso of the switching operation, the order n of the higher harmonic component, the receiving frequency fc of the AM radio broadcast, and a bandwidth BW thereof; and a power supply frequency control means that compares the power supply frequency fs with the upper limit value fs-max and with the lower limit value fs-min for the power supply frequency fs and sets the power supply frequency fs at a value within a range specified by the upper limit value fs-max and the lower limit value fs-min.