| 摘要 |
PROBLEM TO BE SOLVED: To sustain a desired chopping frequency, without increasing the current amplitude by turning first and second switching means off, when a first signal exceeds a second signal. SOLUTION: When a first signal 1 (a signal corresponding to a current actually flowing through the coil of an electric motor, while being subjected to chopping control) exceeds a second signal 2 (a signal for determining a reference current level), both upper and lower transistors 20a, 20b are turned off (hard chop mode) for a predetermined time. Consequently, the coil current falls at a relatively low rate, and since only the lower transistor 20b is turned on (soft chopping mode) subsequently, the coil current falls at a relatively low rate. According to the arrangement, a desired chopping frequency can be sustained without increasing the current amplitude, regardless of the size of the coil inductance. |
