| 摘要 |
PURPOSE:To stabilize an ignition phase angle close to 0 deg. and expand a range of an angle of conduction by a method wherein back electromotive voltage detecting signals are smoothed and compared with reference signals while the detecting signals are slightly put out even when back electromotive voltage is zero. CONSTITUTION:The back electromotive voltage of a DC motor 3 is detected by means of a detecting circuit 4 during an OFF period of a phase controlling switch 6, and inputted to a terminal A of a speed controlling circuit 5. Saw-tooth waves functioning as reference signals are obtained by means of a capacitor C1 in the speed controlling circuit 5, but a forced discharge circuit is mounted in parallel with the capacitor C1 in order to improve accuracy and charge starting voltage is kept constant. The back electromotive voltage inputted to the terminal A is smoothed and equalized by means of a capacitor C2 and inputted to a comparator, but the detecting signals inputted to the comparator are brought to value slightly higher than the charge starting voltage of capacitor C1 by means of bias circuits R1, R2 and a transistor Tr6 at that time even when the back electromotive voltage is zero. |
