JP4712084B2 - Motor drive circuit - Google Patents

Description

  The present invention relates to a motor drive circuit.

  In an electronic device such as a notebook personal computer, a fan motor is used to cool a heat-generating component such as a processor, for example. When cooling a heat-generating component using a fan motor, the cooling performance can be improved by maximizing the motor rotation speed. However, to reduce power consumption and reduce noise, the motor rotates according to the amount of heat generated. Need to adjust speed. For example, in a fan motor, the rotational speed of the motor can be adjusted by increasing or decreasing the drive voltage applied to the motor coil in accordance with the amount of heat generated.

Further, in order to further reduce power consumption and reduce noise, intermittent driving may be performed in addition to driving voltage control. For example, in Patent Document 1, control is performed such that the drive voltage is lowered according to the target rotational speed of the motor, and the rate at which the drive voltage is applied to the motor coil decreases as the target rotational speed of the motor is lowered. A method of controlling to do so is disclosed.
JP 2006-174648 A

  In this way, by reducing the rate at which the drive voltage is applied to the motor coil as the target rotational speed of the motor decreases, the rotational speed of the motor can be increased compared to the case of control only by adjusting the drive voltage. It is possible to control to a low rotation, and it is possible to reduce power consumption and reduce noise.

  By the way, when the motor rotates, cogging torque is generated by attractive force or repulsive force according to the relationship between the position of the magnetic pole and the position of the motor coil. When the motor is stopped, the motor coil is often located where the cogging torque is minimum. Therefore, in order to start rotation from a state where the motor is stopped, torque exceeding the maximum level of cogging torque is required.

  In the method disclosed in Patent Document 1, when the rotational speed of the motor is lowered, the driving voltage is low and the driving rate is also reduced, so that the torque for driving the motor is also reduced. Therefore, when the motor is rotating, it can continue to rotate even with a small torque due to the action of inertia, but when starting to rotate at a low speed from a state where the motor is stopped, the torque that drives the motor is cogging.・ The maximum level of torque cannot be exceeded and startup at low speed may not be possible. In particular, in the case of a single-phase motor, the difference between the maximum level and the minimum level of cogging torque is often larger than that in the case of a three-phase motor.

  The present invention has been made in view of the above problems, and an object thereof is to enable a motor to be started at a low speed.

  In order to achieve the above object, the motor drive circuit of the present invention is a motor drive circuit for driving a single-phase motor, and the drive voltage corresponding to the target rotational speed of the motor increases as one of the logic levels increases. Based on a pulse generation circuit that generates a pulse signal that increases the duty ratio, and a rotation signal corresponding to the rotation of the motor, the duty ratio of the pulse signal when the rotation starts from a state where the motor is stopped A drive control circuit that supplies a drive current to the motor coil that increases as the drive voltage increases during a period of the one logic level at a higher duty ratio, the drive control circuit comprising: When starting rotation from a state where the motor is stopped, the drive current is supplied to the motor coil so that the motor is fully driven. The features.

  The motor can be started at a low speed.

  FIG. 1 is a diagram showing a configuration of a motor drive circuit according to an embodiment of the present invention. The motor drive circuit 10 is incorporated in a fan motor for cooling a heat-generating component (cooled device) such as a processor in an electronic device such as a notebook personal computer, and rotates the cooling fan. Used to drive a motor.

  The motor drive circuit 10 of this embodiment is a circuit that drives a single-phase fan motor, and includes NPN transistors 11 to 14, a drive voltage generation circuit 20, a pulse generation circuit 22, a rotation detection circuit 24, an OR circuit 26, and a control circuit. 28 is comprised. In this embodiment, the motor drive circuit 10 is integrated, a motor coil L is connected between the terminals OUT1 and OUT2, and a voltage Vh1 and a voltage Vh2 according to the rotational position of the motor are connected between the terminals H1 and H2. A Hall element 30 that outputs (rotation signal) is connected, and a signal for controlling the rotation speed of the motor is input from the microcomputer 32 via the terminal CNT. The voltages Vh1 and Vh2 are voltages that change in a sine wave shape having opposite phases.

  The NPN transistors 11 to 14 constitute an H bridge circuit for driving the motor coil L with the drive voltage Vm. For example, when the NPN transistors 11 and 14 are on and the NPN transistors 12 and 13 are off, the motor coil L is driven by the drive voltage Vm so that current flows from the terminal OUT1 to the terminal OUT2. For example, when the NPN transistors 12 and 13 are on and the NPN transistors 11 and 14 are off, the motor coil L is driven by the drive voltage Vm so that current flows from the terminal OUT2 to the terminal OUT1. In addition, when integrating the motor drive circuit 10, it is also possible to provide the NPN transistors 11-14 outside the integrated circuit.

  The drive voltage generation circuit 20 generates a drive voltage Vm that increases as the target rotation speed increases in response to a signal indicating the target rotation speed input from the microcomputer 32. The drive voltage generation circuit 20 can be configured by a regulator circuit that generates the drive voltage Vm by, for example, stepping down a power supply voltage of 5.0 V in accordance with a signal from the microcomputer 32. The drive voltage Vm output from the drive voltage generation circuit 20 is used to drive the motor coil L. Therefore, the rotational speed of the motor increases as the drive voltage Vm increases, and the rotational speed of the motor decreases as the drive voltage Vm decreases.

  The pulse generation circuit 22 generates a pulse signal PWM in which, for example, the H level duty ratio increases as the drive voltage Vm increases. This pulse signal PWM is for driving the motor coil L intermittently. In the present embodiment, when the motor coil L is intermittently driven based on the pulse signal PWM, the motor coil L is driven during a period in which the pulse signal PWM is at the H level. The pulse generation circuit 22 can be realized by using, for example, a reference voltage generation circuit, a triangular wave generation circuit, and a comparison circuit disclosed in Japanese Patent Application Laid-Open No. 2006-174648.

  The rotation detection circuit 24 detects whether or not the motor is rotating based on the voltages Vh1 and Vh2 output from the Hall element 30, and outputs a detection signal DET (rotation detection signal). In the present embodiment, the detection signal DET is at the H level when the motor is stopped, and the detection signal DET is at the L level when the rotation of the motor is detected. In the present embodiment, the rotation of the motor is detected based on the voltages Vh1 and Vh2 output from the Hall element 30, but not limited to the output from the Hall element 30, the frequency according to the rotation speed of the motor It is good also as detecting rotation of a motor using the signal which changes according to rotation of a motor, such as FG (Frequency Generator) signal which becomes.

  The OR circuit 26 outputs a logical sum of the pulse signal PWM output from the pulse generation circuit 22 and the detection signal DET output from the rotation detection circuit 24 as a drive signal DRV. Since the detection signal DET is at the H level during the period from when the motor is stopped until the rotation of the motor is detected, the drive signal DRV is maintained at the H level during this period regardless of the pulse signal PWM. When the rotation of the motor is detected and the detection signal DET becomes L level, the drive signal DRV changes according to the pulse signal PWM.

  The control circuit 28 complementarily turns on and off the NPN transistors 11 and 14 and the NPN transistors 12 and 13 in accordance with the rotational position of the motor. Further, the control circuit 28 appropriately turns on / off the NPN transistors 11 to 14 so that the motor coil L is driven by the drive voltage Vm during the period when the drive signal DRV is at the H level. Therefore, when the drive signal DRV is maintained at the H level, the motor coil L is continuously driven by the drive voltage Vm. On the other hand, when the drive signal DRV changes according to the pulse signal PWM, the motor coil L is intermittently driven by the drive voltage Vm. A state in which the motor coil L is continuously driven by the drive voltage Vm is referred to as full drive.

  The circuit constituted by the rotation detection circuit 24, the OR circuit 26, and the control circuit 28 corresponds to the drive control circuit of the present invention, and the circuit constituted by the OR circuit 26 and the control circuit 28 corresponds to the drive circuit of the present invention. Equivalent to.

  FIG. 2 is a diagram illustrating a configuration example of the rotation detection circuit 24. The rotation detection circuit 24 includes a comparator 40, an edge detection circuit 42, a counter 44, and a detection signal output circuit 46. The comparator 40 outputs a comparison result between the voltages Vh1 and Vh2. In this embodiment, when the voltage Vh1 is higher than the voltage Vh2, the output of the comparator 40 becomes H level, and when the voltage Vh1 is lower than the voltage Vh2, the output of the comparator 40 becomes L level. The edge detection circuit 42 detects an edge of the signal output from the comparator 40, that is, a change from the L level to the H level and a change from the H level to the L level, and outputs a pulse according to the detection of the edge. The counter 44 counts the number of pulses output from the edge detection circuit 42. The detection signal output circuit 46 changes the detection signal DET to L level when the count value of the counter reaches a predetermined value (for example, “4”). When the motor is stopped, the count value of the counter 44 is reset to zero and the detection signal DET is reset to the H level.

  An example of the operation when the motor drive circuit 10 starts rotating from the state where the motor is stopped will be described. FIG. 3 is a diagram illustrating an example of the operation of the rotation detection circuit 24. When the motor is stopped, the voltages Vh1 and Vh2 output from the Hall element 30 do not change, and the signal CMP output from the comparator 40 does not change. In the present embodiment, it is assumed that the signal CMP output from the comparator 40 is at the H level when the motor is stopped.

  When a signal indicating the target rotation speed of the motor is input from the microcomputer 32, the drive voltage generation circuit 20 generates a drive voltage Vm corresponding to the target rotation speed. The pulse generation circuit 22 generates a pulse signal PWM with a duty corresponding to the drive voltage Vm. When the motor is stopped, the count value of the counter 44 is reset to zero, and the detection signal DET output from the detection signal output circuit 46 is reset to H level. Therefore, the drive signal DRV output from the OR circuit 26 is maintained at the H level regardless of the pulse signal PWM. Therefore, the control circuit 28 starts full driving of the motor coil L with the driving voltage Vm. When the motor starts to rotate by full driving, the voltages Vh1 and Vh2 output from the Hall element 30 change according to the rotation of the motor, and the signal CMP output from the comparator 40 also changes. Then, the signal EDGE is output from the edge detection circuit 42 due to the change in the signal CMP, and the count value of the counter 44 increases.

  When the count value of the counter 44 reaches a predetermined value (for example, “4”), it is determined that the motor has started to rotate, and the detection signal DET output from the detection signal output circuit 46 changes to L level. When the detection signal DET becomes L level, the drive signal DRV output from the OR circuit 26 changes according to the pulse signal PWM, and the motor coil L is intermittently driven according to the pulse signal PWM. That is, in the motor drive circuit 10, full driving is performed until the motor starts rotating, and intermittent driving is performed after the motor starts rotating.

  FIG. 4 is a diagram illustrating an example of the relationship between the drive voltage Vm and the rotation speed of the motor. As shown in FIG. 4, the rotational speed increases as the drive voltage Vm increases, and the rotational speed decreases as the drive voltage Vm decreases. In addition, since the duty ratio of the H level increases as the drive voltage Vm increases, the pulse signal PWM has a lower rotation speed in the intermittent drive than in the full drive when the fluctuation range of the drive voltage Vm is the same. Can be controlled. If the duty ratio of the H level of the pulse signal PWM when the drive voltage Vm is at the maximum level (Vmax) is 100%, the maximum rotation speed in the case of intermittent drive becomes the same as that in the case of full drive, and the cooling performance is improved. Can be maintained.

  In a state where the motor is rotating, the rotational speed of the motor can be decreased by decreasing the H level duty ratio of the drive voltage Vm and the pulse signal PWM. When the drive voltage Vm reaches the lowest level (Vmin), the rotation speed of the motor becomes the lowest speed Smin. On the other hand, when it is desired to start the rotation at the rotation speed Smin from the state where the motor is stopped, there is a case where the starting torque exceeding the cogging torque cannot be obtained even if the intermittent driving is started with the drive voltage Vm as Vmin. In other words, when the motor is started by intermittent driving, Va higher than Vmin may be required as the driving voltage Vm. Even in such a case, in the motor drive circuit 10 of the present embodiment, when it is desired to start the rotation at the rotational speed Smin from the state where the motor is stopped, the motor is fully driven until the motor starts rotating. A starting torque exceeding the cogging torque can be obtained, and the rotation of the motor can be started. Then, after the motor starts to rotate, the torque is not required as much as the start-up due to the inertial action, so the motor drive circuit 10 can switch from full drive to intermittent drive, and the rotation speed can be controlled to Smin.

  The motor drive circuit 10 of the present embodiment has been described above. When rotation starts from a state where the motor is stopped, the motor is fully driven by the drive voltage Vm. After the motor starts rotating, the motor is driven by the drive voltage Vm while the PWM signal is at the H level. . Therefore, the motor can be started to rotate even when the drive voltage Vm is such that the motor cannot be rotated only when the PWM signal is at the H level, and the PWM signal is driven only during the period when the PWM signal is at the H level. Compared to the case, the motor can be started at a lower speed.

  By using such a motor drive circuit 10, in an electronic device such as a notebook personal computer, when the heat generation amount of a heat generating component such as a processor is small, the rotation speed of the fan can be made sufficiently low. This makes it possible to reduce power consumption.

  In addition, the said embodiment is for making an understanding of this invention easy, and is not for limiting and interpreting this invention. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes equivalents thereof. For example, in the present embodiment, the drive ratio at the start of rotating the motor is 100%, that is, full drive, but the drive ratio (duty ratio) at the start of rotating the motor is not limited to 100%, and the pulse signal PWM It is sufficient that the ratio is higher than the H level duty ratio. For example, a pulse signal having an H level duty ratio higher than that of the pulse signal PWM may be separately generated, and the motor may be driven by the drive voltage Vm during the H level period of the separately generated pulse signal. For example, in this embodiment, the motor drive circuit 10 is used for driving a single-phase fan motor, but the motor to be driven is not limited to the fan motor, and the number of phases is not limited to a single phase.

It is a figure which shows the structure of the motor drive circuit which is one Embodiment of this invention. It is a figure which shows the structural example of a rotation detection circuit. It is a figure which shows an example of operation | movement of a rotation detection circuit. It is a figure which shows an example of the relationship between a drive voltage and the rotational speed of a motor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Motor drive circuit 11-14 NPN transistor 20 Drive voltage generation circuit 22 Pulse generation circuit 24 Rotation detection circuit 26 OR circuit 28 Control circuit 30 Hall element 32 Microcomputer 40 Comparator 42 Edge detection circuit 44 Counter 46 Detection signal output circuit

Claims (2)

A motor drive circuit for driving a single-phase motor,
A pulse generation circuit that generates a pulse signal in which the duty ratio of one logic level increases as the drive voltage corresponding to the target rotational speed of the motor increases;
Based on a rotation signal corresponding to the rotation of the motor, when the rotation starts from a state where the motor is stopped, the pulse signal has a duty ratio higher than the duty ratio of the pulse signal, and the pulse signal has the one logic level. A drive control circuit that supplies a drive current to the motor coil that increases as the drive voltage increases during the period of
The drive control circuit supplies the drive current to the motor coil so that the motor is fully driven when rotation starts from a state where the motor is stopped. The motor drive circuit according to claim 1,
The drive control circuit includes:
A rotation detection circuit that outputs a rotation detection signal when the motor starts rotating based on the rotation signal;
When the rotation detection signal is not output, the drive current is supplied to the motor coil so that the duty ratio is 100%. When the rotation detection signal is output, the pulse signal is A drive circuit for supplying the drive current to the motor coil during one logic level;
A motor drive circuit comprising:

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