Motor drive control device and motor unit

Abstract

To suppress a brake current while quickly stopping a motor during power shutdown.SOLUTION: A motor drive control device 1 comprises: a control circuit 10, which generates a drive control signal Sd; and a drive circuit 2 which drives a motor 3. The drive circuit 2 comprises: a plurality of switching legs 20u, 20v and 20w including high-side transistors Q1, Q3 and Q5 and low-side transistors Q2, Q4 and Q6 connected in series between a power supply line Vcc and a ground potential GND; and pull-up resistors Ru2, Ru4 and Ru6 connected between the power supply line Vcc and respective control electrodes of the low-side transistors Q2, Q4 and Q6. When detecting that a power supply voltage Vcc is lower than a threshold voltage Vth, the control circuit 10 performs brake control to generate the drive control signal Sd for turning off the high-side transistors Q1, Q3 and Q5 and periodically switching the low-side transistors Q2, Q4 and Q6.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a motor drive control device and a motor unit. [Background technology]

[0002] It is desirable for motors such as brushless DC motors mounted on fans to stop quickly when the power is cut off, etc. To quickly stop the rotation of a motor, a known technique is to brake the motor by turning on a low-side transistor that constitutes the inverter circuit that drives the motor.

[0003] Furthermore, in a fan motor, components for controlling the motor must be mounted within the limited space on the control board, so it is desirable for these individual components to be small.For example, Patent Document 1 discloses a method of providing a boost circuit that boosts the operating voltage of a power supply line to generate a boosted voltage, and turning on the low-side transistor by applying this boosted voltage to the gate of the low-side transistor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-269808 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology disclosed in the aforementioned Patent Document 1 requires a boost circuit that generates a voltage higher than the power supply voltage to control the low-side transistor. Some boost circuits are composed of multiple capacitors and an integrated circuit (IC) for controlling the boost operation. Because the components for controlling a fan motor must be mounted within the limited space on a control board, it is anticipated that there may be cases where it is difficult to place a boost circuit on the control board that generates a boost voltage separate from the power supply voltage in order to control the on / off of the transistor that drives the coil, and an improvement was therefore desired.

[0006] Therefore, prior to filing this application, the inventors of the present application considered a new motor drive control device that allows the components that control the motor to be easily arranged, drives the motor with high efficiency, and can quickly stop the motor when the power is cut off.

[0007] Specifically, the motor drive control device in the prior study by the inventor of the present application includes an inverter circuit for driving a motor, a pre-drive circuit for driving the inverter circuit, and a control circuit consisting of a microcontroller that generates a drive control signal for controlling the drive of the motor and controls the pre-drive circuit. Here, the control circuit operates on a power supply voltage (e.g., 5 V) supplied from a first power supply line, and the pre-drive circuit and the inverter circuit operate on a power supply voltage (e.g., 12 V) supplied from a second power supply line.

[0008] In the motor drive control device of the previously studied example, the pre-drive circuit converts (level shifts) the signal level of the drive control signal output from the control circuit to a signal level based on a power supply voltage (12 V) higher than the power supply voltage (5 V) of the control circuit, and drives the high-side transistor and low-side transistor of the inverter circuit.

[0009] This reduces the on-resistance of the high-side transistor and the low-side transistor, enabling highly efficient motor drive. This level shift conversion is achieved by adding a resistor between the control electrode of the low-side transistor (the gate electrode in the case of a MOS transistor) and the power supply voltage (e.g., 12 V). This allows the power supply voltage to be applied to the control electrode of the low-side transistor through a resistor that requires a relatively small area on the control board.

[0010] Furthermore, this allows the low-side transistor to be forcibly turned on by the pull-up resistor when the power is cut off, making it possible to apply a strong brake to the motor and stop it quickly.

[0011] However, further investigation by the inventors of the present application has revealed that the motor drive control device of the above-mentioned prior art study example has the following problems.

[0012] Specifically, when the power supply to the motor drive control device in the previous study example is cut off, the voltage (5V) on the first power supply line of the control circuit drops faster than the voltage (12V) on the second power supply line of the pre-drive circuit and inverter circuit, so the power supply to the control circuit stops before the voltage on the second power supply line drops sufficiently, rendering the control circuit inoperable.

[0013] This stops the supply of drive control signals from the control circuit to the pre-drive circuit, and the pre-drive circuit stops driving the inverter circuit. At this time, the control electrode of the low-side transistor of the inverter circuit is connected to the power supply line (12V) via a pull-up resistor, so the low-side transistor turns on. This applies a strong brake (short brake) to the motor.

[0014] Generally, the current that flows through the motor coil when braking the motor (hereinafter also referred to as "brake current") increases as the motor's rotational speed increases when the brake is applied. In the case of the above-mentioned prior study example, the motor's rotational speed does not decrease sufficiently when the brake is applied, and the voltage of the power supply line (12 V) does not decrease sufficiently. The inventors of this application have discovered that, after the control circuit stops operating, a very large brake current flows through the low-side transistor whose control electrode is pulled up to the power supply line, causing the low-side transistor to become very hot.

[0015] The present invention is intended to solve at least the above-mentioned problems, and aims to enable the components that control the motor to be easily arranged within the limited space on the control board, and to quickly stop the motor when the power is cut off while suppressing the brake current. [Means for solving the problem]

[0016] A motor drive control device according to a representative embodiment of the present invention includes a control circuit that outputs drive control signals for driving a motor having coils of multiple phases, and a drive circuit that drives the coils based on the drive control signals output from the control circuit, the drive circuit having an inverter circuit with multiple switching legs that drive the coils, a pull-up resistor, and a pre-drive circuit, the switching legs including high-side transistors and low-side transistors connected in series between a power supply line to which a power supply voltage is supplied and a ground potential, a node to which the low-side transistors and the high-side transistors are commonly connected is connected to one end of the corresponding coil, and the low-side transistors the low-side transistor and the high-side transistor have control electrodes for controlling the on / off of the low-side transistor and the high-side transistor, respectively; the pull-up resistor is connected between the control electrode of the low-side transistor and the power supply line; the pre-drive circuit drives the control electrode of the low-side transistor and the control electrode of the high-side transistor in response to the drive control signal; and the control circuit, when detecting that the power supply voltage is lower than a threshold voltage, performs brake control to turn off the high-side transistor in the plurality of switching legs and generate the drive control signal to periodically switch the low-side transistor. [Effects of the Invention]

[0017] According to one aspect of the present invention, the components that control the motor can be easily arranged within the limited space on the control board, making it possible to quickly stop the motor when the power is cut off while suppressing the brake current. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram showing the configuration of a motor unit equipped with a motor drive control device according to an embodiment; [Figure 2]FIG. 2 is a diagram showing a functional block configuration of a control circuit in the motor drive control device according to the embodiment. [Figure 3] 4 is a timing chart showing an example of a drive signal in brake control. [Figure 4A] FIG. 10 is a diagram showing a simulation result of the current of the motor when the power supply is cut off in the motor drive control device according to the embodiment. [Figure 4B] FIG. 10 is a diagram showing the results of a simulation of the current in the motor when the power supply is cut off in a motor drive control device (comparative example) according to a prior study by the inventors of the present application. [Figure 5] FIG. 5 is a diagram showing an example of a temperature change of the low-side transistor of the inverter circuit when the power supply is shut off. DETAILED DESCRIPTION OF THE INVENTION

[0019] 1. Overview of the embodiment First, a typical embodiment of the invention disclosed in this application will be outlined. In the following description, for example, reference numerals in the drawings corresponding to components of the invention are written in parentheses.

[0020] [1] A motor drive control device (1) according to a representative embodiment of the present invention includes a control circuit (10) that outputs a drive control signal (Sd) for driving a motor (3) having coils (Lu, Lv, Lw) of multiple phases, and a drive circuit (2) that drives the coils based on the drive control signal output from the control circuit, the drive circuit including an inverter circuit (2a) having a plurality of switching legs (20u, 20v, 20w) that drive the coils, pull-up resistors (Ru2, Ru4, Ru6), and a pre-drive circuit (2b), the switching legs including high-side transistors (Q1, Q3, Q5) and low-side transistors (Q2, Q4, Q6) connected in series between a power supply line (Vcc) to which a power supply voltage (Vcc) is supplied and a ground potential (GND), and a node where the low-side transistors and the high-side transistors are commonly connected. (Nu, Nv, Nw) are connected to one end of the corresponding coil, the low-side transistor and the high-side transistor have control electrodes (Vuh, Vul, Vvh, Vvl, Vwh, Vwl) for controlling the on / off of the low-side transistor and the high-side transistor, respectively, the pull-up resistor is connected between the control electrode of the low-side transistor and the power supply line, the pre-drive circuit drives the control electrode of the low-side transistor and the control electrode of the high-side transistor in response to the drive control signal, and the control circuit, when detecting that the power supply voltage is lower than a threshold voltage (Vth), performs brake control to turn off the high-side transistor in the multiple switching legs and generate the drive control signal to periodically switch the low-side transistor.

[0021] [2] In the motor drive control device described in [1] above, the control circuit may continue the brake control from the time it detects that the power supply voltage is lower than a threshold voltage until the control circuit becomes inoperable.

[0022] [3] In the motor drive control device described in [1] above, the control circuit may continue the brake control for a predetermined period after detecting that the power supply voltage is lower than the threshold voltage.

[0023] [4] In the motor drive control device according to any one of [1] to [3] above, the signal for driving the low-side transistor among the drive control signals for turning off the high-side transistor and periodically switching the low-side transistor may have a duty ratio of 50% or less.

[0024] [5] A motor unit (100) according to a representative embodiment of the present invention is characterized by comprising the motor drive control device described in any one of [1] to [4] above, and the motor (3).

[0025] 2. Specific examples of embodiments Hereinafter, specific examples of embodiments of the present invention will be described with reference to the drawings. In the following description, components common to the embodiments will be designated by the same reference numerals, and repeated description will be omitted.

[0026] <Embodiment> FIG. 1 is a diagram showing the configuration of a motor unit 100 equipped with a motor drive control device 1 according to an embodiment.

[0027] 1, the motor unit 100 includes a motor 3 and a motor drive control device 1 that controls the rotation of the motor 3. The motor unit 100 can be applied to various devices that use a motor as a drive source, such as a fan.

[0028] The motor 3 is, for example, a permanent magnet synchronous motor. In this embodiment, the motor 3 is, for example, a brushless DC motor having three-phase coils Lu, Lv, and Lw. The coils Lu, Lv, and Lw are, for example, Y-connected to each other.

[0029] The motor drive control device 1 rotates the rotor of the motor 3 by driving the three-phase coils Lu, Lv, and Lw of the motor 3. For example, the motor drive control device 1 applies a sinusoidal drive signal to the motor 3, thereby causing periodic sinusoidal phase currents to flow through the three-phase coils Lu, Lv, and Lw of the motor 3, thereby rotating the rotor.

[0030] The motor drive control device 1 includes, for example, a control circuit 10, a drive circuit 2, a voltage generation circuit 5, and a voltage detection circuit 6. Note that the components of the motor drive control device 1 shown in FIG. 1 are only a part of the whole, and the motor drive control device 1 may have other components in addition to those shown in FIG.

[0031] The voltage generating circuit 5 is a circuit that generates a power supply voltage for the control circuit 10. For example, the voltage generating circuit 5 generates a DC voltage based on a DC voltage Vcc supplied from an external source and supplies the generated DC voltage to the control circuit 10 as a power supply voltage. For example, the voltage generating circuit 5 steps down the DC voltage Vcc (for example, 12 V) to generate a DC voltage Vdd (for example, 5 V). The voltage generating circuit 5 includes a power supply circuit such as a series regulator or a switching regulator.

[0032] The DC voltage Vcc is supplied as a power supply voltage for the drive circuit 2. As described above, the DC voltage Vdd is supplied as a power supply voltage for the control circuit 10. For example, Vdd <Vccである。

[0033] Hereinafter, DC voltage Vcc may be referred to as "power supply voltage Vcc," and DC voltage Vdd may be referred to as "power supply voltage Vdd." Furthermore, the wiring to which power supply voltage Vcc is supplied may be referred to as "power supply line Vcc," and the wiring to which power supply voltage Vdd is supplied may be referred to as "power supply line Vdd."

[0034] The voltage detection circuit 6 is a circuit that detects the power supply voltage Vcc of the drive circuit 2. The voltage detection circuit 6 includes, for example, a resistive voltage divider circuit connected between the power supply line Vcc and the ground potential GND. For example, as shown in FIG. 1, the resistive voltage divider circuit is formed by resistors R1 and R2 connected in series between the power supply line Vcc and the ground potential GND. The voltage detection circuit 6 divides the power supply voltage Vcc and outputs the divided voltage as a voltage detection signal Sv.

[0035] The voltage division ratio based on the resistors R1 and R2 only needs to be adjusted so that the signal level (voltage) of the voltage detection signal Sv is large enough to be input to the control circuit 10. The circuit configuration of the voltage detection circuit 6 is not limited to the above example, and various circuit configurations capable of generating a signal indicating the magnitude of the power supply voltage Vcc can be adopted.

[0036] The drive circuit 2 drives the motor 3 based on a drive control signal Sd output from the control circuit 10. The drive circuit 2 includes, for example, an inverter circuit 2a, a pre-drive circuit 2b, a current detection circuit 2c, and pull-up resistors Ru2, Ru4, and Ru6.

[0037] The inverter circuit 2a is arranged between the power supply line Vcc (power supply voltage Vcc) and ground potential, and drives the multi-phase coils Lu, Lv, and Lw of the motor 3 as a load based on the input drive control signal Sd.

[0038] Specifically, the inverter circuit 2a has a switching leg including at least two drive transistors connected in series, and the two drive transistors alternately perform on / off operations (switching operations) based on the input drive control signal Sd, thereby driving the coils Lu, Lv, and Lw of the motor 3 as a load.

[0039] More specifically, the inverter circuit 2a has switching legs 20u, 20v, and 20w corresponding to the U-phase, V-phase, and W-phase of the motor 3, respectively.

[0040] 1, the switching leg 20u corresponding to the U phase has two drive transistors Q1 and Q2 connected in series between a power supply line Vcc and a ground potential GND via a current detection circuit 2c. A node Nu to which the drive transistors Q1 and Q2 are commonly connected is connected to one end of a coil Lu serving as a load.

[0041] The switching leg 20v corresponding to the V phase has two drive transistors Q3 and Q4 connected in series between the power supply line Vcc and the ground potential GND via a current detection circuit 2c. A node Nv to which the drive transistors Q3 and Q4 are commonly connected is connected to one end of a coil Lv serving as a load.

[0042] The switching leg 20w corresponding to the W phase has two drive transistors Q5 and Q6 connected in series between the power supply line Vcc and the ground potential GND via a current detection circuit 2c. A node Nw to which the drive transistors Q5 and Q6 are commonly connected is connected to one end of a coil Lw as a load.

[0043] The drive transistors Q1 to Q6 each have a control electrode for controlling the drive (on / off) of the drive transistors Q1 to Q6. The drive transistors Q1, Q3, and Q5 are, for example, P-channel MOSFETs, and the gate electrodes of each transistor serve as control electrodes Vuh, Vvh, and Vwh, respectively. The drive transistors Q2, Q4, and Q6 are, for example, N-channel MOSFETs, and the gate electrodes of each transistor serve as control electrodes Vul, Vvl, and Vwl. The drive transistors Q1 to Q6 may also be other types of transistors, such as IGBTs (Insulated Gate Bipolar Transistors).

[0044] Hereinafter, the drive transistors Q2, Q4, and Q6 will also be referred to as "low-side transistors Q2, Q4, and Q6," and the drive transistors Q1, Q3, and Q5 will also be referred to as "high-side transistors Q1, Q3, and Q5." Furthermore, Vuh, Vvh, Vwh, Vul, Vvl, and Vwl represent not only the control electrodes but also the drive signals (voltages) applied to each control electrode.

[0045] The pull-up resistors Ru2, Ru4, and Ru6 are resistors that pull up the control electrodes of the low-side transistors Q2, Q4, and Q6 to the power supply voltage Vcc. Specifically, the pull-up resistor Ru2 is connected between the control electrode Vul of the low-side transistor Q2 and the power supply line Vcc. The pull-up resistor Ru4 is connected between the control electrode Vvl of the low-side transistor Q4 and the power supply line Vcc. The pull-up resistor Ru6 is connected between the control electrode Vwl of the low-side transistor Q6 and the power supply line Vcc.

[0046] Although pull-up resistors are connected between the control electrodes Vuh, Vvh, and Vwh of the high-side transistors Q1, Q3, and Q5 and the power supply line Vcc, these pull-up resistors are not shown in FIG.

[0047] The pre-drive circuit 2b drives the control electrodes Vuh, Vvh, Vwh, Vul, Vvl, and Vwl of the drive transistors Q1 to Q6 in response to the drive control signal Sd output from the control circuit .

[0048] Here, the drive control signal Sd is a signal for controlling the drive of the motor 3, and is, for example, a PWM (Pulse Width Modulation) signal. Specifically, the drive control signal Sd is a signal for switching the current conduction pattern of the coils Lu, Lv, and Lw of the motor 3, which is determined by the on / off states of the drive transistors Q1 to Q6 that make up the inverter circuit 2a. More specifically, the drive control signal Sd includes six types of PWM signals corresponding to the drive transistors Q1 to Q6 of the inverter circuit 2a.

[0049] The pre-drive circuit 2b generates six types of drive signals Vuh, Vul, Vvh, Vvl, Vwh, and Vwl that can supply sufficient power to drive the control electrodes (gate electrodes) of the drive transistors Q1 to Q6 of the inverter circuit 2a, based on six types of PWM signals as drive control signals Sd supplied from the control circuit 10.

[0050] These drive signals Vuh, Vul, Vvh, Vvl, Vwh, and Vwl are input to the control electrodes (gate electrodes) of the drive transistors Q1 to Q6 of the inverter circuit 2a, causing the drive transistors Q1 to Q6 to perform on-off operations (switching operations). For example, the high-side transistors Q1, Q3, and Q5 of the upper arm and the low-side transistors Q2, Q4, and Q6 of the lower arm of the switching leg corresponding to each phase alternately perform on-off operations. As a result, power is supplied from the power supply line Vcc to the coils of each phase of the motor 3, causing the motor 3 to rotate.

[0051] The pre-drive circuit 2b may be provided within the control circuit .

[0052] The current detection circuit 2c is a circuit for detecting currents flowing through the coils Lu, Lv, and Lw of multiple phases of the motor 3. The current detection circuit 2c detects currents (phase currents) flowing through the coils Lu, Lv, and Lw of each phase, and outputs a current detection signal Si corresponding to the detected currents.

[0053] The current detection circuit 2c is connected in series with the inverter circuit 2a, for example, and outputs a signal indicating the phase current of each of the coils Lu, Lv, and Lw as a current detection signal Si.

[0054] For example, the current detection circuit 2c includes at least one resistor (shunt resistor) as a current detection element. The shunt resistor is connected in series with the inverter circuit 2a between the power supply line Vcc and the ground potential (single shunt system). In the present embodiment, as an example, the shunt resistor as the current detection circuit 2c is connected to the negative side (ground side) of the inverter circuit 2a. The current detection circuit 2c converts the phase currents of the coils Lu, Lv, and Lw of the motor 3 into voltages using the resistors, and inputs the voltages to the control circuit 10 as current detection signals Si.

[0055] The position sensor 4 is a device for detecting the rotational position of the rotor of the motor 3. The position sensor 4 outputs a signal corresponding to the rotational position of the rotor. The position sensor 4 is, for example, a Hall element. FIG. 1 shows, as an example, a case where Hall elements are provided as position sensors 4u, 4v, and 4w for the U-phase, V-phase, and W-phase of the motor 3. Hereinafter, the position sensors 4u, 4v, and 4w are also referred to as "Hall elements 4u, 4v, and 4w."

[0056] The Hall elements 4u, 4v, and 4w are arranged, for example, at approximately equal intervals (for example, 120 degrees from adjacent elements) around the rotor of the motor 3. The Hall elements 4u, 4v, and 4w each detect the magnetic poles of the rotor and output Hall signals whose voltages change in response to the rotation of the rotor as rotational position detection signals Hu, Hv, and Hw. The rotational position detection signals Hu, Hv, and Hw are input to the control circuit 10.

[0057] Instead of such a Hall signal, the control circuit 10 may be configured to receive, as a rotational position detection signal, another signal corresponding to the rotational position of the rotor of the motor 3. For example, an encoder, resolver, or the like may be provided, and the detection signal thereof may be input to the control circuit 10.

[0058] The control circuit 10 generates a drive control signal Sd for controlling the operation of the motor 3. The control circuit 10 generates the drive control signal Sd for driving the motor 3 based on, for example, an externally input drive command signal Sc indicating a target state of operation of the motor 3, and controls the operation of the motor 3. For example, the control circuit 10 monitors the rotation state of the motor 3 by obtaining information such as the rotation speed and torque of the rotor of the motor 3 based on the current detection signal Si from the current detection circuit 2c and the rotation position detection signals Hu, Hv, and Hw from the position sensors 4u, 4v, and 4w, and generates a drive control signal Sd to provide the drive circuit 2 so that the motor 3 is in the operating state specified by the drive command signal Sc. The control circuit 10 also monitors the power supply voltage Vcc (power line Vcc) of the drive circuit 2, and performs brake control (described later) when it detects a drop in the power supply voltage Vcc.

[0059] The control circuit 10 is a program processing device (e.g., a microcontroller) having a configuration in which a processor such as a CPU, various storage devices such as RAM and ROM, and peripheral circuits such as a counter (timer), an A / D conversion circuit, a D / A conversion circuit, a clock generation circuit, and an input / output I / F circuit are connected to each other via a bus or dedicated lines.

[0060] In the motor drive control device 1, the control circuit 10 and the drive circuit 2 may each be packaged as separate integrated circuit devices, or at least a portion of the control circuit 10 and at least a portion of the drive circuit 2 may be packaged as a single integrated circuit device (IC).

[0061] FIG. 2 is a diagram showing a functional block configuration of the control circuit 10 in the motor drive control device 1 according to the embodiment.

[0062] As shown in FIG. 2, the control circuit 10 has, for example, a drive command acquisition unit 11, a rotation speed acquisition unit 12, a power supply voltage monitoring unit 13, and a drive control signal generation unit 14 as functional blocks for generating the drive control signal Sd.

[0063] These functional blocks are realized, for example, by a processor in a program processing device serving as the control circuit 10, which executes various arithmetic processes in accordance with programs stored in a memory and controls peripheral circuits such as a counter and an A / D conversion circuit. Note that at least some of these functional blocks may be realized by dedicated hardware logic circuits.

[0064] The drive command acquisition unit 11 receives a drive command signal Sc, for example, from an external source, and analyzes the received drive command signal Sc to acquire a value specifying the target operating state of the motor 3 specified by the drive command signal Sc.

[0065] The drive command signal Sc includes a value indicating a target state of operation of the motor 3. The drive command signal Sc is, for example, a signal output from a higher-level device that is provided outside the motor drive control device 1 and that controls the motor unit 100.

[0066] The drive command signal Sc is, for example, a speed command signal that specifies the rotation speed of the rotor of the motor 3. For example, the drive command signal Sc includes a value of a target rotation speed (target rotation speed) of the rotor of the motor 3. The drive command signal Sc is, for example, a PWM signal having a duty ratio according to the specified target rotation speed. The drive command acquisition unit 11 measures, for example, the duty ratio of the PWM signal serving as the drive command signal Sc, and outputs a rotation speed according to the measured duty ratio as the target rotation speed.

[0067] The rotational speed acquisition unit 12 is a functional unit that acquires a measurement value of the rotational speed of the rotor of the motor 3. The rotational speed acquisition unit 12 calculates the rotational speed of the rotor of the motor 3 by a known calculation method based on the rotational position detection signals Hu, Hv, and Hw output from the position sensors 4u, 4v, and 4w.

[0068] The power supply voltage monitor 13 is a functional unit that monitors the power supply voltage Vcc of the drive circuit 2. The power supply voltage monitor 13 measures the magnitude of the power supply voltage Vcc based on the voltage detection signal Sv output from the voltage detection circuit 6, determines whether the power supply voltage Vcc is lower than a threshold voltage Vth, and outputs a voltage determination signal Sm that indicates the determination result. For example, when the power supply voltage Vcc is higher than the threshold voltage Vth, the power supply voltage monitor 13 outputs a voltage determination signal Sm whose signal level is a first logic level (e.g., low level), and when the power supply voltage Vcc is equal to or lower than the threshold voltage Vth, the power supply voltage monitor 13 outputs a voltage determination signal Sm whose signal level is a second logic level (e.g., high level).

[0069] When the power supply voltage monitor 13 detects that the power supply voltage Vcc has fallen below the threshold voltage Vth, the power supply voltage monitor 13 may fix the signal level of the voltage evaluation signal Sm to the second logic level or reset the threshold voltage Vth to a higher value (hysteresis characteristic). This makes it possible to prevent the signal level of the voltage evaluation signal Sm from frequently switching due to fluctuations in the power supply voltage Vcc.

[0070] The drive control signal generation unit 14 is a functional unit that generates the drive control signal Sd based on at least one of the voltage determination signal Sm output from the power supply voltage monitoring unit 13, the target rotation speed output from the drive command acquisition unit 11, the rotation speed output from the rotation speed acquisition unit 12, and the current detection signal Si output from the current detection circuit 2c.

[0071] Here, the drive control signal Sd includes six types of PWM signals corresponding to the drive signals Vuh, Vvh, Vwh, Vul, Vvl, and Vwl for driving the drive transistors Q1 to Q6 of the inverter circuit 2a, respectively.

[0072] For example, when the power supply voltage Vcc is higher than the threshold voltage Vth (for example, when the voltage determination signal Sm is at a low level), the drive control signal generation unit 14 performs normal control. The normal control is a control in which a PWM signal whose duty ratio is adjusted so that the target rotation speed and the rotation speed output from the rotation speed acquisition unit 12 match, using a known calculation method such as a PID control calculation or a vector control calculation, is generated and output as the drive control signal Sd.

[0073] In normal control, the drive control signal generator 14 may generate a PWM signal with an adjusted duty ratio so that the phase current based on the current detection signal Si does not exceed a predetermined value, and output the PWM signal as the drive control signal Sd.

[0074] On the other hand, when the power supply voltage Vcc is equal to or lower than the threshold voltage Vth (for example, when the voltage determination signal Sm is at a high level), the drive control signal generator 14 performs brake control. The brake control is control that generates a drive control signal Sd that turns off the high-side transistors Q1, Q3, and Q5 and periodically switches the low-side transistors Q2, Q4, and Q6 in the multiple switching legs 20u, 20v, and 20w.

[0075] The drive control signal generating unit 14 continues brake control from the time the control circuit 10 (power supply voltage monitoring unit 13) detects that the power supply voltage Vcc is lower than the threshold voltage Vth (for example, Vcc≦Vth) until the control circuit 10 becomes inoperable.

[0076] Here, the state in which the control circuit 10 is inoperable refers to a state in which the control circuit 10 cannot perform the functions (specifications) required of the control circuit 10 due to, for example, a drop in the power supply voltage Vdd of the control circuit 10.

[0077] The brake control will be described in detail below with reference to the drawings.

[0078] FIG. 3 is a timing chart showing an example of the drive signals Vuh, Vvh, Vwh, Vul, Vvl, and Vwl in brake control.

[0079] In Fig. 3, the horizontal axis represents time and the vertical axis represents the signal level of each signal. From top to bottom, Fig. 3 shows the waveforms of the power supply voltage Vcc, the voltage determination signal Sm, the drive signal Vuh for the high-side transistor Q1, the drive signal Vvh for the high-side transistor Q3, the drive signal Vwh for the high-side transistor Q5, the drive signal Vul for the low-side transistor Q2, the drive signal Vvl for the low-side transistor Q4, and the drive signal Vwl for the low-side transistor Q6.

[0080] For example, the high-side transistors Q1, Q3, and Q5 are turned off when the corresponding drive signals Vuh, Vvh, and Vwh are at a high level and turned on when they are at a low level. The low-side transistors Q2, Q4, and Q6 are turned off when the corresponding drive signals Vul, Vvl, and Vwl are at a low level and turned on when they are at a high level.

[0081] It should be noted that the waveforms of the voltages shown in FIG. 3 are schematic and may differ from the actual waveforms.

[0082] For example, consider a case where the power supply voltage Vcc is higher than the threshold voltage Vth as an initial state. In this case, the power supply voltage monitor 13 outputs a low-level voltage determination signal Sm, and the drive control signal generator 14 generates a drive control signal Sd by normal control to drive the motor 3.

[0083] 3, the supply of power (DC voltage) from the outside to the motor drive control device 1 is stopped. At this time, the voltage of the power supply line Vcc, i.e., the power supply voltage Vcc, begins to gradually decrease due to a stabilizing capacitance connected to the power supply line Vcc, etc.

[0084] For example, when the power supply voltage Vcc becomes equal to or lower than the threshold voltage Vth at time t2, the power supply voltage monitor 13 switches the signal level of the voltage determination signal Sm from low to high. This causes the drive control signal generator 14 to switch from normal control to brake control and generate the drive control signal Sd. More preferably, the drive control signal generator 14 switches from normal control to brake control and generates the drive control signal Sd after a period (dead time) Td during which the high-side transistors Q1, Q3, and Q5 and the low-side transistors Q2, Q4, and Q6 are all turned off has elapsed.

[0085] For example, at time t2, when the drive control signal generator 14 detects that the signal level of the voltage determination signal Sm has switched from low to high, it first turns off both the high-side transistors Q1, Q3, and Q5 and the low-side transistors Q2, Q4, and Q6. Then, at time t3, a predetermined time after time t2, the drive control signal generator 14 starts brake control. During brake control, the drive control signal generator 14 sets the drive signals Vuh, Vvh, and Vwh for the high-side transistors Q1, Q3, and Q5 to high levels and sets the drive signals Vul, Vvl, and Vwl for the low-side transistors Q2, Q4, and Q6 to PWM signals with a predetermined duty ratio. While not particularly limited, the duty ratio of the drive signals Vul, Vvl, and Vwl for the low-side transistors Q2, Q4, and Q6 during brake control is preferably, for example, 50% or less. This prevents the power supply voltage Vcc from rising too much immediately after the start of brake control.

[0086] Thereafter, the drive control signal generator 14 continues to generate the drive control signal Sd by brake control until time t4 when the power supply voltage Vdd drops, the power supply to the control circuit 10 is cut off, and the control circuit 10 becomes inoperable.

[0087] During brake control, while the low-side transistors Q2, Q4, and Q6 are on, the coils Lu, Lv, and Lw of each phase are short-circuited to ground potential, which applies a brake (short brake) to the motor 3, reducing the rotation speed of the motor 3 (rotor).

[0088] On the other hand, during braking control, the rotor rotates by inertia while the low-side transistors Q2, Q4, and Q6 are off. At this time, current flows from the coils Lu, Lv, and Lw of each phase to the power supply line Vcc, causing the power supply voltage Vcc to rise. This causes the power supply voltage Vcc to drop more slowly, which in turn causes the power supply voltage Vdd supplied from the voltage generating circuit 5 to the control circuit 10 to drop more slowly, thereby extending the time the control circuit 10 can operate. In other words, the period during which braking control is performed is longer.

[0089] In this way, the brake control alternately brakes the motor 3 (rotor) while the low-side transistors Q2, Q4, and Q6 are on, and rotates the motor 3 (rotor) by inertia while the low-side transistors Q2, Q4, and Q6 are off. This makes it possible to sufficiently reduce the rotational speed of the motor 3 between when the power is cut off and when the control circuit 10 stops operating, thereby reducing the brake current after the control circuit 10 stops operating.

[0090] FIG. 4A is a diagram showing the simulation results of the current in the motor when the power supply is cut off in the motor drive control device 1 according to the embodiment.

[0091] FIG. 4B is a diagram showing the simulation results of the motor current when the power supply is cut off in the motor drive control device (comparative example) according to the prior study example by the inventor of the present application.

[0092] 4A and 4B, the horizontal axis represents time, and the vertical axis represents the signal level of each signal. In each of the figures, the waveforms of the power supply voltage Vcc, the voltage Vcoil between the two coil phases, and the coil phase current Icoil are shown from top to bottom.

[0093] 4B, in the motor drive control device of the prior study example by the inventor of the present application, when the external power supply is stopped at time tb1 and the control circuit (microcomputer) is powered off at time tb2, the rotation speed of the motor does not decrease sufficiently because brake control is not performed. Therefore, at time tb2, the low-side transistor of the inverter circuit is forcibly turned on by the pull-up resistor, causing a large brake current (current in the coil) to flow.

[0094] In contrast, as shown in Figure 4A, with the motor drive control device 1 according to this embodiment, the brake current generated in the motor after power is shut off from the control circuit 10 is smaller than that in the above-mentioned prior art example. Specifically, when the external power supply is stopped at time ta1 and the power supply voltage Vcc drops below the threshold voltage at time ta2, the control circuit 10 initiates brake control, turning off the high-side transistors Q1, Q3, and Q5 of the inverter circuit 2a and switching the low-side transistors Q2, Q4, and Q6 with a PWM signal having a predetermined duty ratio. This causes the motor 3 to repeatedly brake and coast, thereby facilitating a reduction in the rotational speed of the motor 3.

[0095] Furthermore, as described above, the decrease in the power supply voltage Vcc is gradual due to the brake control, so the control circuit 10 is operable for a longer period of time than in the prior study example. This lengthens the period during which the brake control is performed, further accelerating the decrease in the rotation speed.

[0096] After that, when the control circuit 10 is powered off at time ta3, the low-side transistors Q2, Q4, and Q6 of the inverter circuit 2a are forcibly turned on by the pull-up resistors, and a brake current flows, as in the previous study. At this time, the rotation speed of the motor 3 has sufficiently decreased, so the brake current is significantly smaller than in the previous study, as shown in Figure 4A.

[0097] FIG. 5 is a diagram showing an example of a temperature change of the low-side transistor of the inverter circuit when the power supply is shut off.

[0098] 5, the horizontal axis represents time and the vertical axis represents temperature. Reference numeral 501 represents the change in maximum temperature of the low-side transistor of the inverter circuit before and after power-off in the motor drive control device according to the prior study example, and reference numeral 502 represents the change in maximum temperature of the low-side transistor of the inverter circuit before and after power-off in the motor drive control device 1 according to this embodiment.

[0099] As can be seen from FIG. 5, the motor drive control device 1 according to this embodiment can significantly reduce the brake current of the motor 3 that flows through the low-side transistor after power is cut off, as described above, and therefore can suppress the temperature rise of the low-side transistor compared to the previous study example.

[0100] As described above, the motor drive control device 1 according to this embodiment includes pull-up resistors Ru2, Ru4, and Ru6 connected between the power supply line Vcc and the control electrodes Vul, Vvl, and Vwl of the low-side transistors Q2, Q4, and Q6 of the inverter circuit 2a that drives the motor 3. When the power supply voltage Vcc is lower than the threshold voltage Vth, the motor drive control device 1 performs braking control by turning off the high-side transistors Q1, Q3, and Q5 of the inverter circuit 2a and generating a drive control signal Sd that periodically switches the low-side transistors Q2, Q4, and Q6.

[0101] As described above, this allows the braking operation of the motor 3 and the inertial rotation of the motor 3 to be repeated alternately during the period from when the power supply to the motor drive control device 1 is stopped until the power to the control circuit 10 is shut off, thereby making it possible to sufficiently reduce the rotational speed of the motor 3. As a result, it is possible to suppress the braking current flowing through the motor 3 when the low-side transistors Q2, Q4, and Q6 are forcibly turned on by the pull-up resistors Ru2, Ru4, and Ru6 after the power is shut off.

[0102] As described above, the motor drive control device 1 according to this embodiment makes it possible to quickly stop the motor 3 when the power supply is cut off, while suppressing the brake current.

[0103] Furthermore, the control circuit 10 continues the brake control from when it detects that the power supply voltage Vcc is lower than the threshold voltage Vth until the control circuit 10 becomes inoperable. This allows the period during which the brake control is performed to be extended as much as possible, making it possible to further reduce the rotation speed of the motor 3.

[0104] Furthermore, according to the motor drive control device 1 of this embodiment, a boost circuit for driving the inverter circuit 2a is not required, so it is possible to easily arrange the components that control the motor within the limited space on the control board.

[0105] <<Extension of Embodiment>> The invention made by the inventor has been specifically described above based on an embodiment, but it goes without saying that the invention is not limited thereto and can be modified in various ways without departing from the spirit of the invention.

[0106] For example, in the above embodiment, the control circuit 10 continues brake control from when it detects that the power supply voltage Vcc is lower than the threshold voltage Vth until the control circuit 10 becomes inoperable. However, this is not limited to this. Specifically, the control circuit 10 may continue brake control for a predetermined period after it detects that the power supply voltage Vcc is lower than the threshold voltage Vth. For example, information specifying the implementation period of brake control is stored in advance in a storage device (not shown) within the control circuit 10. The control circuit 10 starts timing using a timer when brake control is started, and stops the brake control when the measured time reaches the implementation period stored in the storage device. This makes it possible to implement brake control for an appropriate period depending on the application to which the motor unit 100 is applied. Furthermore, by rewriting the information specifying the implementation period of brake control, a user or the like can arbitrarily set the implementation period of brake control.

[0107] In the above embodiment, the rotation speed of the motor 3 is calculated based on the position detection signals from the position sensors 4u, 4v, and 4w. However, the present invention is not limited to this. The control circuit 10 (rotation speed acquisition unit 12) may calculate the rotation speed by calculation based on a known sensorless control of the motor. In this case, the position sensors 4u, 4v, and 4w are not required.

[0108] In the above embodiment, the current detection circuit 2c detects the currents of each phase using shunt resistors connected in series to the inverter circuit 2a. However, other known current detection techniques may be used to detect the currents of each phase. For example, the currents of each phase may be detected using shunt resistors connected between the coils of each phase and the common connection point of the drive transistors of the inverter circuit 2a connected to the coils (three-shunt method). Note that if the motor unit 100 is used in an application that does not require current detection, the current detection circuit 2c may not be provided.

[0109] In the above embodiment, the drive command signal Sc is a speed command signal including a target value (target rotation speed) of the rotation speed of the motor 3, but this is not limiting. For example, the drive command signal Sc may be a torque command signal that specifies the torque of the motor 3.

[0110] Furthermore, in the above embodiment, the number of phases of the motor 3 driven by the motor drive control device is not limited to three. [Explanation of symbols]

[0111] 1...motor drive control device, 2...drive circuit, 2a...inverter circuit, 2b...pre-drive circuit, 2c...current detection circuit, 3...motor, 4u, 4v, 4w...position sensor (hall element), 5...voltage generation circuit, 6...voltage detection circuit, 10...control circuit, 11...drive command acquisition unit, 12...rotation speed acquisition unit, 13...power supply voltage monitoring unit, 14...drive control signal generation unit, 20u, 20v, 20w...switching legs, Nu, Nv, Nw...nodes, Q1, Q 3, Q5...high-side transistor, Q2, Q4, Q5...low-side transistor, R1, R2...resistor, Ru2, Ru4, Ru6...pull-up resistor, Vcc...power supply voltage, Vdd...power supply voltage, Vuh, Vul, Vvh, Vvl, Vwh, Vwl...control electrode (drive signal), Sc...drive command signal, Sd...drive control signal, Si...current detection signal, Sm...voltage judgment signal, Sv...voltage detection signal, Hu, Hv, Hw...rotational position detection signal.

Claims

1. a control circuit that outputs a drive control signal for driving a motor having coils of multiple phases; a drive circuit that drives the coil based on the drive control signal output from the control circuit, The drive circuit an inverter circuit having a plurality of switching legs for driving the coil, a pull-up resistor, and a pre-drive circuit; the switching leg includes a high-side transistor and a low-side transistor connected in series between a power supply line to which a power supply voltage is supplied and a ground potential; a node to which the low-side transistor and the high-side transistor are commonly connected is connected to one end of the corresponding coil; the low-side transistor and the high-side transistor each have a control electrode for controlling the low-side transistor and the high-side transistor to be turned on and off; the pull-up resistor is connected between the control electrode of the low-side transistor and the power supply line; the pre-drive circuit drives the control electrode of the low-side transistor and the control electrode of the high-side transistor in response to the drive control signal; When the control circuit detects that the power supply voltage is lower than a threshold voltage, the control circuit performs brake control to turn off the high-side transistors in the plurality of switching legs and generate the drive control signal to periodically switch the low-side transistors. Motor drive control device.

2. 2. The motor drive control device according to claim 1, The control circuit continues the brake control from when it detects that the power supply voltage is lower than a threshold voltage until the control circuit becomes inoperable. Motor drive control device.

3. 2. The motor drive control device according to claim 1, The control circuit continues the brake control for a predetermined period after detecting that the power supply voltage is lower than the threshold voltage. Motor drive control device.

4. 2. The motor drive control device according to claim 1, The signal for driving the low-side transistor among the drive control signals for turning off the high-side transistor and periodically switching the low-side transistor has a duty ratio of 50% or less. Motor drive control device.

5. A motor drive control device according to any one of claims 1 to 4; the motor; Motor unit.

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