Drive control circuit for linear vibration motor
View Patent ↗A drive signal generating unit generates a drive signal used to alternately deliver a positive current and a negative current to a coil with a nonconducting period inserted between conducting periods. A driver unit generates a drive current in response to the drive signal generated by the drive signal generating unit and supplies the drive current to a coil. The drive signal generating unit estimates the eigen frequency of a linear vibration motor based on a detected position of the zero cross occurring in the coil during the nonconducting period, and the frequency of the drive signal is brought close to the estimated eigen frequency. The zero-cross detecting unit sets a detection window for avoiding the detection of zero cross of voltages other than the induced voltage. The zero-cross detecting unit enables a zero cross detected within the detection window and disables a zero cross detected outside the detection window.
1. A drive control circuit of a linear vibration motor, having a stator and a vibrator at least one of which is constituted by an electromagnet, which vibrates the vibrator relative to the stator by supplying a drive current to a coil of the electromagnet, the drive control circuit comprising:
a drive signal generating unit configured to generate a drive signal used to alternately deliver a positive current and a negative current to the coil with an nonconducting period inserted between conducting periods;
a driver unit configured to generate the drive current in response to the drive signal generated by said drive signal generating unit so as to supply the drive current to the coil;
an induced voltage detector configured to detect an induced voltage occurring in the coil during the nonconducting period; and
a zero-cross detecting unit configured to detect a zero cross of the induced voltage detected by said induced voltage detector,
wherein said drive signal generating unit estimates an eigen frequency of the linear vibration motor based on a detected position of the zero cross thereof, and the frequency of the drive signal is brought close to the estimated eigen frequency, and
wherein said zero-cross detecting unit sets a detection window for avoiding the detection of zero cross of voltages other than the induced voltage, and
said zero-cross detecting unit enables a zero cross detected within the detection window and disables a zero cross detected outside the detection window.
2. A drive control circuit of a linear vibration motor according to claim 1 , wherein when the zero cross is not detected within the detection window and the zero cross of the induced voltage has been completed at a start position of the detection window, said zero-cross detecting unit assumes that a zero cross has been detected in the neighborhood of the start position of the detection window and supplies the assumed detection position of the zero cross to said drive signal generating unit.
3. A drive control circuit of a linear vibration motor according to claim 2 , said zero-cross detecting unit including:
a comparator configured to compare the induced voltage detected by said induced voltage detector with a reference voltage used to detect the zero cross;
an edge detector configured to detect a position where an output of the comparator is inverted, as an edge; and
an output control unit configured to supply an edge position detected by the edge detector, as the detection position of the zero cross, to said drive signal generating unit when the output of the comparator is not inverted at the start position of the detection window, and
configured supply the start position of the detection window, as the detection position of the zero cross, to said drive signal generating unit, when the output of the comparator has already been inverted at the start position of the detection window.
4. A drive control circuit of a linear vibration motor according to claim 1 , wherein when the zero cross is not detected within the detection window and the zero cross of the induced voltage has not been completed at an end position of the detection window, said zero-cross detecting unit assumes that a zero cross has been detected in the neighborhood of the end position of the detection window and supplies the assumed detection position of the zero cross to said drive signal generating unit.
5. A drive control circuit of a linear vibration motor according to claim 4 , wherein said induced voltage detector detects a voltage across the coil in a conducting period of the drive signal,
said zero-cross detecting unit including:
a comparator configured to compare the voltage across the coil detected by said induced voltage detector with a reference voltage used to detect the zero cross; and
an edge detector configured to detect a position where an output of the comparator is inverted, as an edge,
wherein the end position of the detection window extends to a position containing a start position of a subsequent conducting period, and
wherein the comparator inverts the output thereof by not only the zero cross of the induced voltage but also the zero cross of the drive voltage supplied during the conducting period.