| 摘要 |
PURPOSE:To provide a drive circuit for brushless motor employing no rotation detector wherein counter-electromotive force can be detected accurately in OFF section of output voltage and the motor can be decelerated forcibly. CONSTITUTION:Zero-cross point of counter-electromotive force is detected and a synthesized driving waveform created utilizing the timing of zero-cross point is inputted to two comparators 5, 6 where it is compared with voltage references 1, 2. Outputs from two comparators are fed to an AND circuit 7 and thus ANDed output is employed as a switching signal for turning an analog switch 8 OFF thereby turning a predetermined section of an output voltage from a power amplifier 4, including the zero-cross point, forcibly OFF to produce a high impedance section. According to the constitution, zero-cross point of counter-electromotive force can be detected easily and a motor can be decelerated forcibly. |
