Recently, there grows societal tendency toward safety, low-fuel consumption, and pollution reduction of vehicles, and thus a field of automotive electronics is rapidly developed. In such a background, for example, an automatic transmission having little transmission shock and variable intake and exhaustion valves of an engine come to be employed for a vehicle.
A linear solenoid, which is a kind of actuator (load), is driven by a driving circuit such as an Electronic Control Unit (ECU) to be able to supply the hydraulic pressure of lines that is linearly changed in accordance with control current. Therefore, by employing a linear solenoid for control over a planetary gear, a lock-up clutch, and the line pressure of a transmission of a vehicle, it is possible to reduce a transmission shock and to improve the fuel consumption. Moreover, by employing a linear solenoid for control over an open/close operation of variable intake and exhaustion valves of an engine, it is possible to improve the cleanliness of exhaust gas, torque, output power, and fuel consumption.
For example, a technology is disclosed, which is for reducing degradation in response performance of a linear solenoid caused by the viscosity of oil for generating the hydraulic pressure of lines so as to slightly vibrate (dither) a movable body of the linear solenoid around a predetermined position (see Japanese Laid-open Patent Publication No. 08-303628, for example). The linear solenoid alternately outputs Pulse-Width-Modulation pulses (PWM pulses) based on two Duty ratios for each predetermined time interval and drives and slightly vibrates a movable body of the linear solenoid so as to reduce the frictional resistance, whereby the movable body is rapidly moved in changing its position so as to improve the response performance.
However, the aforementioned conventional technology performs current feedback from a linear solenoid for each period of the PWM pulse for generating a dither, and thus there exists a problem that processing load for generating a dither increases.