JP2003061366A - Motor driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform high-speed switching while preventing kick back. SOLUTION: A p-channel transistor 26 for drawing charge is connected to the gate of a sink-side n-channel transistor 10b. Drive signals of the transistor 10b are supplied to the gate of the transistor 10b via two inverters 24, 20, and the input signals of the inverters 24 are fed to the gate of the transistor 26. With this structure, when the transistor 10b is turned off, the transistor 26 is turned on, and a voltage at the gate of the transistor 10b drops from a voltage at its 'on' time at high speed. Also, the transistor 26 is turned off automatically when the gate of the transistor 10b reaches the voltage at which it is actually turned off. Therefore, characteristics at the actual turning-off time can be separately adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor drive circuit for controlling a drive current to a motor coil, and more particularly to on / off control of a transistor forming the circuit.

[0002]

2. Description of the Related Art Conventionally, electric motors have been used for various operations in cameras. For example, in a normal camera, a motor is used not only for driving a shutter, auto focus (AF), film, and diaphragm, but also for winding a film. In addition, an actuator may be used to move the lens to prevent camera shake. As described above, although a plurality of motors are used in the digital camera, a voice coil motor, a stepping motor, an ultrasonic motor, or the like is used depending on the application.

Further, these motors control the current supplied to the motor to control the operation thereof.
Transistors are used, especially PWM (pulse width modulation)
Control is utilized.

In this PWM control, the accuracy can be improved by increasing the carrier frequency, and noise can be prevented by setting the frequency above the audible range. On the other hand, a bipolar transistor cannot be turned on and off at high speed, but by using a MOS transistor as the transistor, the transistor can be turned on and off at high speed.

Therefore, by using a MOS transistor in a motor driver and performing PWM control of this MOS transistor, highly accurate and high speed motor drive control can be achieved.

[0006]

However, the motor is driven by energizing the motor coil, and when the MOS transistor is turned on and off at high speed, the energization current of the coil located ahead of it is turned on and off at high speed. When the current for the L component such as in the coil is changed at high speed, kickback occurs correspondingly, which causes a problem that a high voltage is generated at the output terminal of the IC.

To this end, switching of the MOS transistor may be blunted. However, if the switching is blunted, not only the control frequency cannot be increased, but also the possibility that the through current flows increases. That is, when current is supplied to the motor coil from the source side transistor, current is drawn from the sink side transistor, and the transistor is turned on and off, the probability that both the source side and sink side transistors are turned on increases. In particular, when the carrier frequency is high, it is impossible to avoid the generation of shoot-through current when trying to avoid a high voltage due to kickback.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a motor drive circuit capable of effectively reducing the influence of kickback while preventing the occurrence of through current. .

[0009]

The present invention has two output transistors on the source side and the sink side, which are arranged in series between a power supply and ground, and the connection point of these two output transistors is connected to one end of the motor coil. Is a motor drive circuit for controlling a motor drive current by connecting to a gate of the sink-side output transistor to a control transistor whose other end is connected to ground, and turning off the sink-side output transistor. The signal turns on.

As described above, according to the present invention, when the sink-side output transistor is turned off, the control transistor connecting the gate to the ground is turned on. Therefore, the control transistor discharges the electric charge accumulated in the parasitic capacitance between the gate and the ground to the sink side output transistor.

The present invention has two n-channel transistors on the source side and the sink side which are arranged in series between the power source and the ground, and the connection point of these two n-channel transistors is connected to one end of the motor coil. A motor drive circuit for controlling a motor drive current, wherein a p-channel transistor having the other end connected to the ground is connected to the gate of the sink-side n-channel transistor.
The channel transistor is turned on by a signal for turning off the sink side n-channel transistor.

Thus, according to the present invention, the sink side n
When turning off the channel transistor, the p-channel transistor that connects its gate to ground is turned on. Therefore, the p-channel transistor discharges the electric charge accumulated in the parasitic capacitance between the gate and the ground to the sink-side n-channel transistor. When the gate potential of the sink-side n-channel transistor becomes low, this p-channel transistor loses its potential difference from its own gate and is turned off. Therefore, sink side n
In the operation of turning off the channel transistor, it is turned off at a preset speed. As a result, high-speed off can be achieved while preventing the occurrence of kickback due to the off of the sink side n-channel transistor. Further, since the charge is rapidly extracted by the p-channel transistor, the time required to turn off the sink-side n-channel transistor does not depend on the change in the power supply voltage,
It becomes easy to control so that a through current does not occur.

A high voltage power source having a voltage higher than the power source voltage and a P channel transistor and an n channel transistor which are arranged in series between the ground and are driven by a control signal to the gate of the sink side n channel transistor. It is preferable to have an inverter and a resistance for current adjustment arranged between the gate of the sink side n-channel transistor and the inverter.

Further, the p-channel transistor is
It is preferable to turn off the sink-side n-channel transistor before turning off.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a motor drive circuit according to an embodiment.

Power supply VM (eg 6V) and ground G
A source side n-channel transistor (source side transistor) 10a, a sink side n-channel transistor (sink side transistor) 10b are connected in series between ND, a source side n-channel transistor (source side transistor) 12a, and a sink side. and an n-channel transistor (sink-side transistor) 12b connected in series. Then, the source side transistor 10a
The motor coil 14 is connected between the intermediate point of the sink side transistor 10b, the intermediate point of the source side transistor 12a, and the intermediate point of the sink side transistor 12b.

Therefore, the source side transistor 10a,
Turning on the sink side transistor 12b causes a current to flow in the motor coil 14 toward the right in the figure, and turning on the source side transistor 12a and the sink side transistor 10b causes a current to flow to the motor coil 14 toward the left in the figure. Flows.

In this example, the motor is a voice coil motor, and the movement of a driven body (for example, a magnet) can be controlled by controlling the energization of one motor coil 14. In particular, in this embodiment, PWM control is performed to turn each transistor on and off at a predetermined duty ratio. For example, the carrier frequency is about 64 kHz, and the duty ratio accuracy is 8 bits (256 divisions). Then, in this way, each transistor is turned on / off by the signal with the duty ratio set.

In this voice coil motor, the duty ratio is set to 50%, and the source side transistor 10a and the sink side transistor 12b are turned on alternately with the source side transistor 12a and the sink side transistor 10b to be turned on. Is stopped. And
By moving the duty ratio, the driven body is moved according to the duty ratio.

A PWM signal is supplied to the gate of the source side transistor 10a via an inverter 16. The gate of the source side transistor 12a is supplied with a PWM signal having a reverse phase to the PWM drive signal supplied to the gate of the source side transistor 10a.

The inverter 16 comprises a p-channel transistor 16a on the power source side and an n-channel transistor 16b on the ground side connected in series. The power source to which the p-channel transistor 16a is connected is the above-mentioned power source VM.
The power source VG has a higher voltage. This power supply VG
Is set to about 9.5V, which is about 3.5V higher than the power supply VM to turn on the n-channel transistor 10a. Then, the signal is input to the gate of the input signal, and the output from the intermediate point between the p-channel transistor 16a and the n-channel transistor 16b is output to the source side transistor 10
a is supplied to the gate.

An inverter 20 is connected to the gate of the sink side transistor 10b via a resistor 18. The inverter 20 includes a p-channel transistor 20a and an n-channel transistor 20b,
The p-channel transistor 20 is connected to the power supply VG. And the midpoint and n-channel transistor 2
A resistor 22 is inserted between 0b and 0b.

The p-channel transistor 20a and the n-channel transistor 20 of this inverter 20 are
The output of the inverter 24 is connected to the gate of b. This inverter 24 is also composed of a p-channel transistor 24a arranged between the power source VG and the ground and an n-channel transistor 24b connected in series. The connection point of both transistors is output, and the PWM drive signal is supplied to the gates of both transistors. To be done.

The output of the inverter 20 is connected to an extraction p-channel transistor (extraction transistor) 26 having the other end connected to the ground. The extraction transistor 26 has a gate connected to the inverter 24. Is supplied with the PWM signal.

Although illustration is omitted, a circuit similar to the inverter 16 is connected to the gate of the source side transistor 12a, and a circuit similar to the inverters 20 and 24 and the transistor 26 is connected to the gate of the sink side transistor 12b. Are connected.

Next, the operation of the circuit of this embodiment will be described. First, a signal (a CPU, for example) for controlling the overall operation of the digital camera outputs a signal for determining the operation of the voice coil. If the CPU has a PWM output port, a PWM signal (first and second PWM signals) is output from this. The duty ratio of this PWM signal is determined by the CPU based on various signals.

The first PWM signal is supplied to the gate of the transistor 10a via the inverter 16 and also via the inverters 24 and 20 to the transistor 10b.
Is supplied to the gate. Therefore, the transistor 10a,
10b is driven in reverse phase.

Here, when the transistor 10b is rapidly turned off, so-called kickback occurs due to the interruption of the current flowing through the motor coil 14, and the end portion of the motor coil 14 (the intermediate point between the transistors 10a and 10b). The voltage rises. Then, the power source VM may rise due to the parasitic diode formed in parallel with the transistor 10a, and a voltage higher than the withstand voltage may be applied to various members.

Of course, although the regeneration capacitor C1 is arranged in the immediate vicinity of the VM terminal, if the kickback energy is strong, the VM may rise.

Therefore, in this embodiment, the resistor 22 is provided to adjust the change in the gate potential of the transistor 10b. That is, the transistor 10b
A parasitic capacitance is formed between the gate and the ground. In the ON state of the transistor 10b, the gate is raised to the voltage of the power source VG, and this voltage charges the parasitic capacitance. Then, the degree to which the transistor 20b of the inverter 20 is turned on and the gate potential of the transistor 10b drops can be adjusted by the size of the resistor 22. Therefore, by adjusting the size of the resistor 22, the speed at which the transistor 10b is switched from on to off can be set to an appropriate speed to prevent the above-mentioned adverse effects of kickback.

However, as mentioned above, the transistor 10
The gate potential of b is raised to the power supply voltage VG. Therefore, it takes a considerable time to decrease from the power supply voltage VG (for example, 9.5 V) to the voltage Ve (threshold value) until the transistor 10b is turned off. That is, as shown by the broken line in FIG.
It takes quite a while to turn off the 10b.

On the other hand, the transistor 10b starts to be turned off only when the gate voltage becomes about 3V or less. Therefore, in order to slowly turn off the transistor 10b and reduce kickback, it is sufficient to turn off slowly from 3.5V.

In this embodiment, the transistor 26 is provided. The gate of the transistor 26 is
The first PWM signal is supplied as it is. Therefore, when the transistor 10b is turned on, the transistor 2
Although 6 is off, it turns on immediately when the first PWM signal goes to L to turn off the transistor 10b. As a result, a current flows from the gate of the transistor 10b to the ground via the transistor 26, and the gate of the transistor 10b rapidly drops. Then, when the gate potential of the transistor 10b becomes about 4 V or less, the potential difference between the gate and the drain of the transistor 26 becomes insufficient and the transistor 26 is turned off.

Therefore, as indicated by the solid line in FIG. 2, when the transistor 10b is turned off, the gate potential of the transistor 10b is lowered at a high speed by the transistor 26 being turned on initially, and when the transistor 10b is actually turned off, the resistor 22 is turned on. The current flows at the speed set by the function of and is turned off.

Further, in the structure of this embodiment, the gate potential of the transistor 10b decreases to 4V for a very short time, and the off time thereafter is constant. Therefore,
Even if the power supply voltage VG fluctuates, the time required to turn off the transistor 10b can always be kept substantially constant.

Without the transistor 26, the time until the gate voltage of the transistor 10b reaches 4V is greatly affected by the power supply voltage VG, and therefore the off time of the transistor 10b changes due to the fluctuation of the power supply voltage VG, and various This variation had to be taken into account in the treatment. However, according to this embodiment, such a problem can be solved. Therefore, since the MOS transistor can be turned off gently, generation of an excessive kick-up voltage can be suppressed and high-speed PWM control can be performed.

In the above description, the transistors 10a, 1
Although it has been described that 0b is driven by a signal having a completely opposite phase, a through current is generated in the off time of the transistor 10b. Therefore, a delay corresponding to the off time is added to the PWM signal to the gate of the source side transistor 10a,
In addition, it is preferable to add a circuit that turns off the transistor 10a when the transistor 10b turns on. The delay circuit can be configured by connecting a suitable number of inverters in series, for example. Further, by inputting the input signal to the inverter 16 through the OR gate and connecting the gate of the transistor 10b to the other input terminal of this OR gate, the transistor 10a is not turned on when the gate of the transistor 10b is at the H level. Can be configured as

In the above description, the transistors 10a, 1
Although only 0b is described, the transistors 12a, 1
The same applies to 2b.

Furthermore, although the voice coil motor has been described in the above example, the present invention can be similarly applied to a stepping motor, a DC motor with a brush, or the like. In this case, the number of coils increases, and the number of source side transistors and sink side transistors increases correspondingly.

In the above example, the source side transistors 10a and 12a are not provided with the extraction transistor 26, but the sink side transistor 10b and
A transistor for extraction may be provided as a drive circuit configuration similar to that of 12b.

[0041]

As described above, according to the present invention,
When the sink-side n-channel transistor is turned off, the p-channel transistor that connects its gate to ground is turned on. Therefore, the p-channel transistor pulls out the charge accumulated in the parasitic capacitance between the gate and the ground on the sink-side n-channel transistor. When the gate potential of the sink-side n-channel transistor becomes low, this p-channel transistor loses its potential difference from its own gate and is turned off. Therefore,
In the operation of turning off the sink-side n-channel transistor, the turning-off is performed at a preset speed.
As a result, it is possible to achieve high-speed off while preventing the occurrence of excessive kickback due to the off of the sink side n-channel transistor. Further, since the charge is extracted at a high speed by the p-channel transistor, the time required for turning off the sink-side n-channel transistor does not depend on the change in the power supply voltage, and it is easy to control so that a through current does not occur.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment.

FIG. 2 is a diagram showing a change in gate potential when a sink-side n-channel transistor is off.

[Explanation of symbols]

10, 12, 26 transistors, 14 motor coils, 18, 22 resistors, 16, 20, 24 inverters.

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Claims (4)

[Claims] 1. A power source and a ground side have two output transistors of a source side and a sink side which are arranged in series, and a connection point of these two output transistors is connected to one end of a motor coil to supply a motor drive current. A motor drive circuit for controlling, wherein the gate of the sink-side output transistor is connected to a control transistor whose other end is connected to ground, and the control transistor is turned on by a signal for turning off the sink-side output transistor. . 2. A motor drive device having two source-side and sink-side n-channel transistors arranged in series between a power supply and a ground, and connecting a connection point of the two n-channel transistors to one end of a motor coil. A motor drive circuit for controlling current, wherein a p-channel transistor having the other end connected to ground is connected to the gate of the sink-side n-channel transistor, and the p-channel transistor is connected to the sink-side n-channel transistor.
A motor drive circuit that is turned on by a signal that turns off the channel transistor. 3. The circuit according to claim 2, comprising a P-channel transistor and an n-channel transistor arranged in series between a high-voltage power supply having a voltage higher than the power supply voltage and a ground, and the sink-side n-channel transistor. A motor drive circuit having an inverter driven by a control signal to the gate and a resistor for current adjustment arranged between the gate of the sink side n-channel transistor and the inverter. 4. The motor drive circuit according to claim 2, wherein the p-channel transistor is turned off before the sink-side n-channel transistor is turned off.