| 摘要 |
In order to ensures a stable reduction of noise level at all times, in the steps of switching input voltage with a switching element (10), smoothing the voltage of rectangular wave obtained by switching with a reactor L and capacitor Cf and outputting it, the voltage obtained by dividing the output voltage is compared with the sawtooth wave output from a sawtooth wave generator (14) by a comparator (12). When the switching signal in response to the result of this comparison is applied to the switching element (10), the counter (16) is actuated synchronously with the vertex of the sawtooth wave to perform opening/closing operation of the switch SW1. The time constant of the time constant circuit comprising a R0 and C is adjusted according to whether a resistor R1 is present or not, and the signals of frequencies f1 and f2 coming out of the sawtooth wave generator (14) are sequentially switched to be sent to the comparator (12). The peak of the switching noise is diffused in the frequency range by sequential selection of switching frequencies, and noise level is reduced by diffusion of noise energy. <IMAGE> |
