| 摘要 |
PROBLEM TO BE SOLVED: To lower the noise level under a steady, stable condition. SOLUTION: A switching element 10 alternates between ON and OFF for an input voltage, producing a square wave, of which voltage is smoothed via a reactor L and capacitor Cf and is output. In the above process, a voltage obtained by dividing the output voltage and a sawtooth output from a sawtooth generator 14 are compared at a comparator 12, and a switching signal corresponding to the result of the comparison is applied to the switching element 10. At this point, a counter 16 performs in synchronism with the peak of the square wave to open and close a switch SW1, regulating the time constant of a time constant circuit consisting of R0 and C by switching on and off a resistance R1. The signals of frequencies f1 and f2 generated by the sawtooth generator 14 are switched sequentially giving them to the comparator 12. By switching the switching frequency sequentially, the peaks of switching noises are diffused in the frequency region and the energy of the noises is dispersed, so that the noise level is lowered.
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