Patent ID: 8618881

Claim:
A class-D power amplifier comprising: a switching power source section that includes: a first switching section which switches a DC power source output having a predetermined voltage at a first frequency; a transformer section which inputs an output from the first switching section to a primary coil thereof and takes out a converted output from a secondary coil thereof; a rectification section which rectifies the converted output taken out of the secondary coil of the transformer section; and a feedback section which controls switching of the first switching section by applying a feedback to the first switching section from the rectification section to maintain a voltage of the converted output from the rectification section constant; a synchronization signal generation section that includes a filter circuit which takes out of the switching power source section a clock signal having a second frequency which is â€œnâ€ times of the first frequency, wherein â€œnâ€ is an integer of two or more; and a class-D power amplifying section that includes: a comparator which compares an input signal with a feedback signal; a second switching section which switches a power source fed from the rectification section according to an output from the comparator; a filter section which smoothes an output from the second switching section to form an output signal; and a combining section which delays a phase of the output signal from the filter section and which combines the delayed output signal with a clock signal from the synchronization signal generation section to generate the feedback signal, wherein the class-D power amplifying section is tuned so as to cause self-oscillating operation at a frequency which is substantially identical with the second frequency, where a level of the output signal from the filter section is lower than that of the clock signal from the synchronization signal generation section.