1. Field of the Invention
The present invention relates to a motor drive circuit.
2. Description of the Related Art
With respect to a linear motor that drives an actuator for performing positioning of a magnetic head of a hard disc drive, a voice coil motor is generally known that produces thrust by passing an electric current through a coil in a magnetic field of a permanent magnet. Recently, there have been portable terminals such as cellular phones and notebook personal computers equipped with camera modules in which the voice coil motors may be used to perform auto-focusing control and optical zoom control in order to reduce the sizes of the modules.
For example, Japanese Patent Laid-Open Publication No. 2008-178206 discloses an actuator drive device capable of reducing vibration of a moving part by changing a drive current of the voice coil motor at a certain gradient in a time period which is a substantially natural-number multiple of the natural frequency period of the moving part.
As such, the position of the moving part of the actuator can swiftly be stabilized by supplying to the voice coil motor the drive current having a ramp waveform which changes at a certain gradient.
The natural frequency period, however, varies by the configuration of the actuator, and the actuator drive device of Japanese Patent Laid-Open Publication No. 2008-178206 requires that the time period in which the drive current is ramped up should be set longer as the natural frequency (resonance frequency) becomes lower.
For this reason, the convergence time, in which the vibration of the actuator has converged and the position of the moving part has been stabilized, may become longer, so that the response speed required for the module to be used may not be satisfied.