| 摘要 |
PURPOSE:To reduce the effect by AC magnetic field, by constituting the entire circuit with one chip C-MOS IC. CONSTITUTION:The drive circuit and amplifying section is formed with P type MOSFET gates 21 and 22, N type MOSFET gates 23 to 26, detection resistors 28 and 29 and motor 20. The voltage induced in the coil by external magnetic field is shortened with the closed loop of the N gates 23 and 24. The N gates 23 and 24 are transistors for motor drive and ON resistance is about 10 ohms. Thus, the voltage induced in the coil is shortened and comparatively greater current flows. Next, switching is made to the closed loop of the motor 20, N gates 26 and 23, detection resistor 29. Since the coil of the motor 20 has an inductive component, comparatively greater current keeps flowing, a greater voltage is produced across the detection resistor 29 for a moment, and the voltage is in steady state which is determined with the detection resistor 29, induced voltage by external magnetic field, and coil resistance. Accordingly, without using special detection element, AC magnetic field can be detected with low power consumption and the drive current of motor can be controlled to achieve initial objective. |
