| 摘要 |
PURPOSE:To prevent production of audible noise by an arrangement wherein a chopper signal having not constant frequency is outputted from a chopper signal generating means. CONSTITUTION:A chopper signal generating means 11 comprises a pseudo- random signal generator 12 comprising a single Ex-OR gate and four shift registers and an oscillator 13 generating pulse signals having constant frequency, and the chopper signal generating means 11 outputs a chopper signal CHP having frequency variable at pseudo-random. A PWM chopper control circuit 22 performs chopper control based on the chopper signal CHP and outputs a drive signal DRV for turning a switching element 21 ON/OFF. According to the arrangement, production of audible noise due to resonance can be prevented because the oscillation of inductive load is not periodic. |
