| 摘要 |
PURPOSE:To automatically regulate to a suitable value a switching frequency in response to a noise level and a timbre according to the operating states from low to high speed operations by automatically regulating the hysteresis width of a comparator in response to the motor speed. CONSTITUTION:When the speed of an induction machine IM is lower than the speed set in a speed detector NH, an analog switch AS is opened, and the hysteresis width of a comparator COM is regulated to a wide value by the ratio of resistors R1 to R2. On the contrary, when the speed of the machine IM is higher than the speed set in the detector NH, the switch AS is closed to regulate the width to a narrow value of the ratio of the resistor R2 to the resistance R of the parallel resistance value. Accordingly, the switching frequency of transistors Q1-Q6 becomes low in low speed operation and high in high speed operation. |
