JP2024135298A - Motor driver circuits, electronic devices - Google Patents

Abstract

To provide a motor driver circuit capable of detecting a zero cross of a back electromotive force with high accuracy.SOLUTION: A U-phase output pin VU is connected with a U-phase coil of a three-phase DC motor. A neutral point pin COM is connected so as to receive a neutral point voltage VCOM of the three-phase motor. When a power supply voltage of a three-phase inverter circuit 110 is defined as Vcc, a neutral point clamp circuit 260 outputs a neutral point clamp voltage VCOM' corresponding to a voltage obtained by clamping a neutral point voltage VCOM generated in the neutral point pin so as not to exceed a first clamp level which is determined on the basis of Vcc/2. A U-phase clamp circuit 250U outputs a U-phase clamp voltage VU' corresponding to a voltage obtained by clamping a U-phase voltage VU generated in the U-phase output pin VU so as not to exceed a second clamp level VCL2 which is determined higher than the first clamp level VCL1.SELECTED DRAWING: Figure 2

Description

This disclosure relates to a motor driver circuit.

Half-bridge circuits, H-bridge circuits, and three-phase bridge circuits (collectively referred to as bridge circuits below) that use power transistors are widely used in motor driver circuits, DC/DC converters, power conversion devices, and the like.

The bridge circuit has an upper arm and a lower arm arranged in series between a power supply terminal and a ground terminal for each phase. The upper arm includes a high-side transistor and a flywheel diode connected in parallel. The lower arm includes a low-side transistor and a flywheel diode connected in parallel.

To rotate a brushless DC motor, the drive phase must be switched in sequence according to the rotor position. There are two drive methods for brushless DC motors: a sensor method using a Hall element and a sensorless method that does not use a Hall element. In the sensorless method, the drive phase is switched by detecting the timing when the back electromotive force (BEMF: Back Electromotive Force) generated in the coils of each phase of the motor becomes zero.

The detection of back electromotive force is performed by a comparator. When detecting back electromotive force, the output of the inverter for each phase is set to high impedance. In this state, the comparator detects the timing at which the back electromotive force becomes zero by comparing the voltage at the neutral point of the three-phase motor with the output voltage of the inverter for each phase.

Patent No. 7169815

When the power supply voltage of the inverter is Vcc, the voltage at the neutral point of a three-phase motor is kept near Vcc/2, while the output voltage of the inverter for each phase swings between the power supply voltage Vcc and 0 V. Therefore, if the output of the inverter is to be directly input to a comparator, the comparator is required to have a high withstand voltage.

To lower the voltage resistance required of the comparator, a method is sometimes used in which a voltage divider circuit that divides the inverter's output voltage and a voltage divider circuit that divides the neutral point voltage at the same voltage division ratio are provided on the input side of the comparator, and the divided output voltage and neutral point voltage are input to the comparator. This method can lower the voltage resistance required of the comparator by increasing the voltage division ratio.

However, if there is variation in the voltage division ratio of the voltage divider circuit for the output voltage and the voltage division ratio of the voltage divider circuit for the neutral point voltage, there is a problem that the detection accuracy decreases. In addition, the resistance and parasitic capacitance of the voltage divider circuit form a filter, which may reduce the detection speed.

The present disclosure has been made in light of such circumstances, and one exemplary purpose of one aspect thereof is to provide a motor driver circuit capable of detecting the zero crossing of the back electromotive force with high accuracy.

An aspect of the present disclosure relates to a motor driver circuit for driving a three-phase DC motor. The motor driver circuit includes a U-phase output pin to be connected to a U-phase coil of the three-phase DC motor, a V-phase output pin to be connected to a V-phase coil of the three-phase DC motor, a W-phase output pin to be connected to a W-phase coil of the three-phase DC motor, a neutral pin to be connected to receive a neutral point voltage of the three-phase DC motor, a neutral point clamp circuit that outputs a neutral point clamp voltage equivalent to a voltage clamped so as not to exceed a first clamp level determined based on Vcc/2 when the power supply voltage of the three-phase inverter circuit is Vcc, and a U-phase clamp circuit that outputs a U-phase clamp voltage equivalent to a voltage clamped so as not to exceed a second clamp level determined higher than the first clamp level when the power supply voltage of the three-phase inverter circuit is Vcc. The three-phase inverter circuit includes a V-phase clamp circuit, a V-phase clamp circuit that outputs a V-phase clamp voltage equivalent to a voltage obtained by clamping the V-phase voltage generated at the V-phase output pin so that it does not exceed a second clamp level, a W-phase clamp circuit that outputs a W-phase clamp voltage equivalent to a voltage obtained by clamping the W-phase voltage generated at the W-phase output pin so that it does not exceed the second clamp level, a U-phase comparison circuit that compares the U-phase clamp voltage with a neutral point clamp voltage, a V-phase comparison circuit that compares the V-phase clamp voltage with the neutral point clamp voltage, a W-phase comparison circuit that compares the W-phase clamp voltage with the neutral point clamp voltage, and a control circuit that generates a control signal for controlling the three-phase inverter circuit based on the outputs of the U-phase comparison circuit, the V-phase comparison circuit, and the W-phase comparison circuit.

In addition, any combination of the above components, or mutual substitution of components or expressions between methods, devices, systems, etc., are also valid aspects of the present invention.

According to certain aspects of the present disclosure, it is possible to detect the zero crossing of the back electromotive force with high accuracy.

FIG. 1 is a circuit diagram of a motor circuit including a motor driver circuit according to an embodiment. FIG. 2 is a circuit diagram of the motor driver circuit according to the embodiment. FIG. 3 is an operational waveform diagram of the motor driver circuit of FIG. FIG. 4 is a circuit diagram showing an example of the configuration of the U-phase back electromotive force detection circuit. FIG. 5 is a circuit diagram showing an example of the U-phase back electromotive force detection circuit of FIG. FIG. 6 is a circuit diagram showing another example of the U-phase back electromotive force detection circuit of FIG. FIG. 7 is a circuit diagram showing a modification of the U-phase comparator circuit. FIG. 8 is a circuit diagram showing a modification of the U-phase back electromotive force detection circuit.

(Overview of the embodiment)
A summary of some exemplary embodiments of the present disclosure will be described. This summary is intended to provide a simplified description of some concepts of one or more embodiments for the purpose of providing a basic understanding of the embodiments as a prelude to the detailed description that follows, and is not intended to limit the scope of the invention or disclosure. For convenience, the term "one embodiment" may be used to refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed in this specification.

This summary is not an exhaustive overview of all possible embodiments, and is not intended to identify key elements of all embodiments or to delineate the scope of some or all aspects. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

A motor driver circuit according to one embodiment includes a U-phase output pin to be connected to a U-phase coil of a three-phase DC motor, a V-phase output pin to be connected to a V-phase coil of a three-phase DC motor, a W-phase output pin to be connected to a W-phase coil of a three-phase DC motor, a neutral pin to be connected to receive a neutral point voltage of the three-phase DC motor, a neutral point clamp circuit that outputs a neutral point clamp voltage equivalent to a voltage clamped so that the neutral point voltage does not exceed a first clamp level determined based on Vcc/2 when the power supply voltage of the three-phase inverter circuit is Vcc, and a U-phase clamp voltage equivalent to a voltage clamped so that the U-phase voltage generated at the U-phase output pin does not exceed a second clamp level determined to be higher than the first clamp level. The inverter circuit includes a U-phase clamp circuit that outputs a V-phase clamp voltage equivalent to a voltage obtained by clamping the V-phase voltage generated at the V-phase output pin so that it does not exceed a second clamp level, a W-phase clamp circuit that outputs a W-phase clamp voltage equivalent to a voltage obtained by clamping the W-phase voltage generated at the W-phase output pin so that it does not exceed the second clamp level, a U-phase comparison circuit that compares the U-phase clamp voltage with a neutral point clamp voltage, a V-phase comparison circuit that compares the V-phase clamp voltage with the neutral point clamp voltage, a W-phase comparison circuit that compares the W-phase clamp voltage with the neutral point clamp voltage, and a control circuit that generates a control signal for controlling the three-phase inverter circuit based on the outputs of the U-phase comparison circuit, the V-phase comparison circuit, and the W-phase comparison circuit.

When the motor circuit is operating normally, the neutral point voltage of the three-phase DC motor is maintained near the midpoint voltage Vcc/2 of the power supply voltage Vcc. In addition, since what is required for zero-cross detection of the back electromotive force is the timing at which each phase voltage crosses the neutral point voltage, there is no need to monitor phase voltages that are significantly higher than the neutral point voltage. Therefore, using the midpoint voltage Vcc/2 under normal conditions as a reference, the neutral point voltage is clamped by setting a first clamp level at a level equal to or slightly higher than the midpoint voltage Vcc/2, and the phase voltages are clamped by setting a second clamp level at a level higher than the first clamp level. The neutral point voltage and phase voltages after clamping are compared, thereby enabling zero-cross detection of the back electromotive force. Since the maximum voltage of the neutral point voltage and phase voltages after clamping that are to be compared is a clamp level close to the midpoint voltage Vcc/2, the withstand voltage required for the comparison circuit can be reduced.

In one embodiment, the neutral clamp circuit may include a first voltage clamp element connected between the neutral pin and ground.

In one embodiment, the U-phase clamp circuit, the V-phase clamp circuit, and the W-phase clamp circuit may each include a second voltage clamp element connected between the corresponding output pin and ground.

In one embodiment, the neutral point clamp circuit may further include a first resistor connected between the neutral point pin and the first voltage clamp element. Each of the U-phase clamp circuit, the V-phase clamp circuit, and the W-phase clamp circuit may further include a second resistor connected between the corresponding output pin and the second voltage clamp element. The first resistor and the second resistor of each phase may be paired.

In one embodiment, the U-phase clamp circuit, the V-phase clamp circuit, and the W-phase clamp circuit may each include a third voltage clamp element connected between the corresponding output pin and the neutral pin.

In one embodiment, the neutral point clamp circuit may further include a first resistor connected between the neutral point pin and the first voltage clamp element. Each of the U-phase clamp circuit, the V-phase clamp circuit, and the W-phase clamp circuit may further include a third resistor connected between the corresponding output pin and the third voltage clamp element. The first resistor and the third resistor of each phase may be paired.

In one embodiment, the U-phase comparison circuit, the V-phase comparison circuit, and the W-phase comparison circuit may each include a voltage comparator having a first input that receives the clamp voltage of the corresponding phase and a second input that receives the neutral point clamp voltage.

In one embodiment, the U-phase comparison circuit, the V-phase comparison circuit, and the W-phase comparison circuit may each include a neutral point voltage divider circuit that divides the neutral point clamp voltage, a phase voltage divider circuit that divides the clamp voltage of the corresponding phase, and a voltage comparator having a first input that receives the output voltage of the phase voltage divider circuit, and a second input that receives the output voltage of the neutral point voltage divider circuit.

In one embodiment, the phase voltage divider circuit may be shared by the U-phase comparison circuit, the V-phase comparison circuit, and the W-phase comparison circuit.

In one embodiment, the motor driver circuit may be monolithically integrated on a single semiconductor substrate. "Monolithic integration" includes cases where all of the circuit components are formed on a semiconductor substrate, and cases where the main components of the circuit are monolithically integrated, and some resistors, capacitors, etc. may be provided outside the semiconductor substrate for adjusting the circuit constants. By integrating the circuit on a single chip, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

In one embodiment, the three-phase inverter circuit may be constructed using discrete elements outside the motor driver circuit.

(Embodiment)
Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and duplicated descriptions will be omitted as appropriate. In addition, the embodiments are illustrative and do not limit the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, "a state in which component A is connected to component B" includes not only cases in which component A and component B are directly physically connected, but also cases in which component A and component B are indirectly connected via other components that do not substantially affect their electrical connection state or impair the function or effect achieved by their combination.

Similarly, "a state in which component C is provided between components A and B" includes not only cases in which components A and C, or components B and C, are directly connected, but also cases in which they are indirectly connected via other components that do not substantially affect their electrical connection state or impair the function or effect achieved by their combination.

Figure 1 is a circuit diagram of a motor circuit 100 including a motor driver circuit 200 according to an embodiment. The motor circuit 100 includes a three-phase DC motor 2, a three-phase inverter circuit 110, and a motor driver circuit 200. The three-phase DC motor 2 includes a U-phase coil, a V-phase coil, and a W-phase coil. A tap is drawn from the neutral point, which is the connection point of the U-phase coil, the V-phase coil, and the W-phase coil.

The three-phase inverter circuit 110 is a three-phase bridge circuit and includes inverters (legs) of U, V, and W phases. In the following, for ease of explanation, U, V, and W will be represented as # and generalized. The #-phase inverter includes a high-side transistor MH# and a low-side transistor ML# connected between the power supply line 112 and the ground line 114. The connection node between the high-side transistor MH# and the low-side transistor ML# is the output of the #-phase inverter and is connected to the corresponding #-phase coil.

The motor driver circuit 200 is an integrated circuit (IC) integrated on a single semiconductor substrate, and controls the three-phase inverter circuit 110 so that the three-phase DC motor 2 rotates in a target state. For example, the motor driver circuit 200 may stabilize the rotation speed of the three-phase DC motor 2, or may stabilize the rotor position of the three-phase DC motor 2, and the control method is not particularly limited. The energization method is also not particularly limited, and may be a 120-degree energization method (rectangular wave drive method) or a 180-degree energization method (sine wave drive method).

The motor driver circuit 200 has a U-phase output pin VU, a V-phase output pin VV, a W-phase output pin VW, and a neutral pin COM. The U-phase output pin VU is connected to the U-phase coil of the three-phase DC motor 2, in other words, the output of the U-phase inverter. Similarly, the V-phase output pin VV is connected to the V-phase coil, and the W-phase output pin VW is connected to the W-phase coil.

The neutral pin COM is connected to receive a neutral voltage _VCOM of the three-phase DC motor 2. In this example, the neutral pin COM is connected to an actual neutral point of the three-phase DC motor 2, but the present disclosure is not limited thereto, and the neutral pin COM may be connected to a virtual neutral point.

The U-phase back electromotive force detection circuit 240U compares the U-phase voltage _VU with the neutral point voltage _VCOM and outputs a detection signal BEMFU indicating the comparison result. In the case of the 120-degree conduction method, the U-phase back electromotive force detection circuit 240U operates during a period when no current flows through the U-phase coil. In the case of the 180-degree conduction method, a time window is set by predicting the timing of the zero crossing of the back electromotive force, and during this time window, the output of the U-phase inverter is made high impedance and the back electromotive force is monitored.

The V-phase back electromotive force detection circuit 240V compares the V-phase voltage _VV with the neutral point voltage _VCOM and outputs a detection signal BEMFV indicative of the comparison result. The W-phase back electromotive force detection circuit 240W compares the W-phase voltage _VW with the neutral point voltage _VCOM and outputs a detection signal BEMFW indicative of the comparison result.

The control circuit 230 generates control signals HCTRLU, HCTRLV, HCTRLW, LCTRLU, LCTRLV, and LCTRLW for controlling the three-phase inverter circuit 110 based on the detection signals BEMFU, BEMFV, and BEMFW generated by the U-phase comparison circuit 270U, V-phase comparison circuit 270V, and W-phase comparison circuit 270W.

The U-phase high-side pre-driver 210U drives the high-side transistor MHU of the corresponding phase based on a control signal HCTRLU. The same is true for the V-phase low-side pre-driver 210V and the W-phase low-side pre-driver 210W. In general, the high-side pre-driver 210# drives the high-side transistor MH# based on a control signal HCTRL#.

The U-phase low-side pre-driver 220U drives the low-side transistor MLU of the corresponding phase based on a control signal LCTRLU. The same is true for the V-phase low-side pre-driver 220V and the W-phase low-side pre-driver 220W. In general, the low-side pre-driver 220# drives the low-side transistor ML# based on a control signal LCTRL#.

The above is the configuration of the motor driver circuit 200.

Figure 2 is a circuit diagram of a motor driver circuit 200 according to an embodiment. Figure 2 shows the configurations of the U-phase back electromotive force detection circuit 240U, the V-phase back electromotive force detection circuit 240V, and the W-phase back electromotive force detection circuit 240W in Figure 1.

The U-phase clamp circuit 250U and the U-phase comparison circuit 270U, together with the neutral point clamp circuit 260, constitute the U-phase back EMF detection circuit 240U in FIG. 1. The same is true for the V-phase and W-phase, so the configuration of the U-phase will be explained as a representative.

The power supply voltage of the three-phase inverter circuit 110 in a normal state is Vcc. The neutral point clamp circuit 260 clamps the neutral point voltage _VCOM generated at the neutral point pin COM so that it does not exceed a first clamp level _VCL1 determined based on Vcc/2, and outputs a neutral point clamp voltage _VCOM ' generated as a result of the clamping.

The U-phase clamp circuit 250U outputs a U-phase clamp voltage _VU ' equivalent to a voltage obtained by clamping the U-phase voltage _VU generated at the U-phase output pin VU so that it does not exceed a second clamp level _VCL2 . The second clamp level _VCL2 is set higher than the first clamp level _VCL1 .

The U-phase comparison circuit 270U compares the U-phase clamp voltage V _U ' with the neutral point clamp voltage V _COM ', and outputs a detection signal BEMFU indicative of the comparison result.

The above is the configuration of the motor driver circuit 200. Next, we will explain its operation.

Fig. 3 is an operation waveform diagram of the motor driver circuit 200 in Fig. 2. Here, detection of U-phase back electromotive force will be described using the 120-degree energization method as an example. Fig. 3 shows the three-phase back electromotive forces _VBEMFU to _VBEMFW , the states of the three-phase high-side transistors MHU to MHW, the states of the three-phase low-side transistors MLU to MLW, the U-phase voltage _VU , the energization state of the U-phase, the U-phase clamp voltage VU', and the detection signal BEMFU.

In the energized section of the U-phase, the U-phase voltage _VU is the power supply voltage _VCC or the ground voltage 0 V. In the non-energized section, the U-phase voltage _VU is the back electromotive force _VBEMFU of the U-phase coil.

The neutral point voltage V _COM is lower than the first clamp level V _CL1 , so the neutral point clamp voltage V _COM ' is equal to the neutral point voltage V _COM .

The U-phase clamp voltage _VU ' is a voltage obtained by clamping the U-phase voltage _VU at a second clamp level _VCL2 . In the non-energized section of the U-phase, the U-phase clamp voltage _VU ' is compared with the clamped neutral point voltage _VCOM ' (= _VCOM ), and a detection signal BEMFU is generated according to the comparison result. The edges of the detection signal BEMFU marked with arrows indicate the timing at which detection should be performed.

The above is the operation of the motor driver circuit 200. Next, we will explain its advantages.

According to the motor driver circuit 200, the neutral point clamp voltage V _COM ' input to the U-phase comparison circuit 270U is guaranteed to be lower than the first clamp level V _CL1 , and the U-phase clamp voltage V _U ' is guaranteed to be lower than the second clamp level V _CL2 . Therefore, the withstand voltage of the U-phase comparison circuit 270U may be designed assuming the second clamp level V _CL2 .

In the motor driver circuit 200 in FIG. 2, a resistive voltage divider circuit is not directly connected to the U-phase output pin VU. As a result, high-speed back electromotive force detection is possible.

Furthermore, compared to a configuration in which the phase voltage and neutral voltage are divided at the same voltage division ratio, this configuration is not affected by errors in the voltage division ratio caused by manufacturing variability, making it possible to detect back EMF with high accuracy.

This disclosure covers various devices and methods that can be understood as the block diagram or circuit diagram of FIG. 2 or derived from the above description, and is not limited to a specific configuration. Below, more specific configuration examples and examples are described, not to narrow the scope of this disclosure, but to aid in understanding and clarify the essence and operation of this disclosure and the present invention.

Figure 4 is a circuit diagram showing an example of the configuration of the U-phase back electromotive force detection circuit 240U. Here, the U-phase is explained, but U can be read as V or W.

The U-phase clamp circuit 250U includes a second resistor R2 and a second voltage clamp circuit 252. The second voltage clamp circuit 252 is connected to the neutral pin COM via the first resistor R1. The second voltage clamp circuit 252 clamps the potential of a node 253. As shown in FIG. 3, the phase voltage _VU rises to near the power supply voltage _Vcc in the conduction section. By inserting the first resistor R1, the potential of the node 253 can be clamped without affecting the switching operation.

The neutral point clamp circuit 260 includes a first resistor R1 and a first voltage clamp circuit 262. The first voltage clamp circuit 262 is connected to the neutral point pin COM via the first resistor R1. The first voltage clamp circuit 262 clamps the potential of the node 263. The first resistor R1 has the same resistance value as the second resistor R2.

During normal operation, the neutral point voltage _VCOM is lower than the first clamp level _VCL1 , so the first resistor R1 of the neutral point clamp circuit 260 is not necessary, but by adding the first resistor R1, the U-phase clamp circuit 250U and the neutral point clamp circuit 260 have the same configuration, so the accuracy of voltage detection can be improved. It is preferable that the first resistor R1 and the second resistor R2 have the same element configuration on the semiconductor substrate and are arranged adjacent to each other. This is called pairing.

The U-phase comparison circuit 270U includes a voltage comparator 272. The voltage comparator 272 receives the U-phase clamp voltage V _U ' at a first input and the neutral point clamp voltage V _COM ' at a second input. The voltage comparator 272 outputs a detection signal BEMFU that indicates the magnitude relationship between the two voltages V _U ' and V _COM '.

Fig. 5 is a circuit diagram showing an example of the U-phase back electromotive force detection circuit 240U of Fig. 4. The first voltage clamp circuit 262 includes a Zener diode ZD1 that is a first voltage clamp element connected between a node 263 and the ground. When the Zener voltage of the Zener diode ZD1 is Vz, the voltage V _COM ' at the node 263 is clamped with _VZ as the upper limit level. In other words, V _CL1 = _VZ .

The second voltage clamp circuit 252 includes a Zener diode ZD2 and a diode D2 that are second voltage clamp elements connected in series between the node 253 and ground. When the Zener voltage of the Zener diode ZD2 is Vz and the forward voltage of the diode D2 is Vf, the voltage V _U ' at the node 253 is clamped with V _Z +Vf as the upper limit level. In other words, V _CL2 =V _Z +Vf.

Fig. 6 is a circuit diagram showing another example of the U-phase back electromotive force detection circuit 240U of Fig. 4. The second voltage clamp circuit 252 of Fig. 6 includes a diode D3 serving as a third voltage clamp element connected between the node 253 and the node 263. A third resistor R3 is connected between the node 253 and the U-phase output pin VU. The third resistor R3 and the first resistor R1 are paired. With this configuration as well, the voltage _VU ' of the node 253 can be clamped with _VZ +Vf as the upper limit level.

The configuration of the clamp circuit is not limited to using rectifying elements such as Zener diodes or diodes, and may be configured as a source follower circuit or an emitter follower circuit.

The embodiments are merely examples, and those skilled in the art will understand that various modifications are possible in the combination of each component and each processing process, and that such modifications are also within the scope of this disclosure or the present invention. The following describes such modifications.

7 is a circuit diagram showing a modified example of the U-phase comparison circuit 270U. This modified example is useful when the neutral point voltage V _COM is higher than the withstand voltage of the voltage comparator 272. The U-phase comparison circuit 270U includes a neutral point voltage dividing circuit 274 and a phase voltage dividing circuit 276 in addition to the voltage comparator 272. The neutral point voltage dividing circuit 274 divides the neutral point clamp voltage V _COM '. The phase voltage dividing circuit 276 divides the U-phase clamp voltage V _U ' at the same voltage division ratio. The voltage comparator 272 compares the neutral point clamp voltage V _COM " after voltage division with the U-phase clamp voltage V _U " after voltage division.

The neutral point voltage dividing circuit 274 is shared by the U-phase comparison circuit 270U, the V-phase comparison circuit 270V, and the W-phase comparison circuit 270W, and the neutral point clamp voltage V _COM ″ after voltage division is also supplied to the voltage comparators 272 of the V-phase comparison circuit 270V and the W-phase comparison circuit 270W.

The advantages of the configuration in Fig. 7 will be described in comparison with a comparative technique. The comparative technique is a configuration in which the U-phase clamp circuit 250U and the neutral point clamp circuit 260 are omitted from the configuration in Fig. 7, and the U-phase voltage _VU is directly input to the phase voltage U dividing circuit 276, and the neutral point voltage _VCOM is directly input to the neutral point dividing circuit 274.

Assume now that the withstand voltage of the voltage comparator 272 is 10V, and the power supply voltage V _CC of the three-phase inverter circuit 110 is 40V. In this case, the maximum level of the U-phase voltage V _U is 40V, and the neutral point voltage V _COM is about 20V. In the comparison technique, the U-phase voltage V _U of 40V needs to be reduced to 10V or less, so the voltage division ratio of the voltage divider circuit 276 needs to be 1/4 (or less). The voltage division ratio of the neutral point voltage divider circuit 274 also needs to be 1/4. In this case, the neutral point voltage V _COM '' input to the voltage comparator 272 is 20V x 1/4 = 5V. In other words, in the comparison technique, two voltages V _COM '' and V _U '' near 5V are compared.

7, the U-phase clamp voltage V _U ', which is the input to the phase voltage U voltage dividing circuit 276, is clamped to a voltage level slightly higher than the neutral point voltage V _COM , and therefore its maximum level is about 20V. Therefore, in the configuration of FIG. 7, the phase voltage U voltage dividing circuit 276 only needs to lower the U-phase clamp voltage V _U ' of 20V to 10V or less, and the voltage dividing ratio of the voltage dividing circuit 276 can be set to 1/2 (or less). The voltage dividing ratio of the neutral point voltage dividing circuit 274 is similar and can be set to 1/2. At this time, the neutral point voltage V _COM '' input to the voltage comparator 272 is 20V x 1/2 = 10V. That is, in the configuration of FIG. 7, two voltages V _COM '' and V _U '' near 10V are compared.

The voltage comparator 272 has an input offset voltage, and the smaller the input voltage, the more significant the effect of the input offset voltage becomes, and the lower the accuracy of the voltage comparison becomes. In the configuration of FIG. 7, the input voltage is doubled compared to the comparison technique, making it possible to perform a more accurate voltage comparison.

Figure 8 is a circuit diagram showing a modified example of the U-phase back electromotive force detection circuit 240U. In this modified example, the first resistor R1 is replaced with a first switch SW1, and the second resistor R2 or the third resistor R3 is replaced with a second switch SW2. The first switch SW1 and the second switch SW2 are turned on only during the back electromotive force detection interval and are turned off during other intervals.

In the embodiment, the bridge circuit 110 is configured with discrete components, but this is not limited thereto, and the bridge circuit 110 may be integrated into the drive circuit 400.

The embodiments are illustrative, and it will be understood by those skilled in the art that there are various variations in the combination of each component and each processing process, and that such variations are also included within the scope of this disclosure or the present invention.

100 Motor circuit 2 Three-phase DC motor 110 Three-phase inverter circuit 112 Inverter circuit 200 Motor driver circuit 210U U-phase high-side pre-driver 210V V-phase high-side pre-driver 210W W-phase high-side pre-driver 220U U-phase low-side pre-driver 220V V-phase low-side pre-driver 220W W-phase low-side pre-driver 230 Control circuit 240U U-phase back electromotive force detection circuit 240V V-phase back electromotive force detection circuit 240W W-phase back electromotive force detection circuit 250U U-phase clamp circuit 250V V-phase clamp circuit 250W W-phase clamp circuit 252 Second voltage clamp circuit 260 Neutral point clamp circuit 262 First voltage clamp circuit 270U U-phase comparison circuit 270V V-phase comparison circuit 270W W-phase comparison circuit 272 Voltage comparator 274 Neutral point voltage divider circuit 276 Phase voltage divider circuit R1 First resistor R2 Second resistor R3 Third resistor SW1 First switch SW2 Second switch

Claims (14)

A motor driver circuit for driving a three-phase DC motor, comprising:
a U-phase output pin to be connected to a U-phase coil of the three-phase DC motor;
a V-phase output pin to be connected to a V-phase coil of the three-phase DC motor;
a W-phase output pin to be connected to a W-phase coil of the three-phase DC motor;
a neutral pin to be connected to receive a neutral voltage of the three-phase DC motor;
a neutral point clamp circuit that outputs a neutral point clamp voltage corresponding to a voltage obtained by clamping the neutral point voltage so as not to exceed a first clamp level determined based on Vcc/2, when a power supply voltage of the three-phase inverter circuit is Vcc;
a U-phase clamp circuit that outputs a U-phase clamp voltage corresponding to a voltage obtained by clamping a U-phase voltage generated at the U-phase output pin so as not to exceed a second clamp level that is set higher than the first clamp level;
a V-phase clamp circuit that outputs a V-phase clamp voltage corresponding to a voltage obtained by clamping a V-phase voltage generated at the V-phase output pin so as not to exceed the second clamp level;
a W-phase clamp circuit that outputs a W-phase clamp voltage corresponding to a voltage obtained by clamping a W-phase voltage generated at the W-phase output pin so as not to exceed the second clamp level;
a U-phase comparison circuit for comparing the U-phase clamp voltage with the neutral point clamp voltage;
a V-phase comparison circuit for comparing the V-phase clamp voltage with the neutral point clamp voltage;
a W-phase comparison circuit for comparing the W-phase clamp voltage with the neutral point clamp voltage;
a control circuit that generates a control signal for controlling the three-phase inverter circuit based on outputs of the U-phase comparison circuit, the V-phase comparison circuit, and the W-phase comparison circuit;
A motor driver circuit comprising: The motor driver circuit of claim 1, wherein the neutral point clamp circuit includes a first voltage clamp element connected between the neutral point pin and ground. The U-phase clamp circuit, the V-phase clamp circuit, and the W-phase clamp circuit each include
3. The motor driver circuit of claim 2, further comprising a second voltage clamp element connected between the corresponding output pin and ground. the neutral point clamp circuit further includes a first resistor connected between the neutral point pin and the first voltage clamp element;
each of the U-phase clamp circuit, the V-phase clamp circuit, and the W-phase clamp circuit further includes a second resistor connected between the corresponding output pin and the second voltage clamp element;
The motor driver circuit according to claim 3 , wherein the first resistor and the second resistor of each phase are paired. The U-phase clamp circuit, the V-phase clamp circuit, and the W-phase clamp circuit each include
3. The motor driver circuit of claim 2, further comprising a third voltage clamp element connected between a corresponding output pin and said neutral pin. the neutral point clamp circuit further includes a first resistor connected between the neutral point pin and the first voltage clamp element;
each of the U-phase clamp circuit, the V-phase clamp circuit, and the W-phase clamp circuit further includes a third resistor connected between the corresponding output pin and the third voltage clamp element;
The motor driver circuit according to claim 5 , wherein the first resistor and the third resistor of each phase are paired. The U-phase comparison circuit, the V-phase comparison circuit, and the W-phase comparison circuit each include
7. A motor driver circuit as claimed in claim 1, including a voltage comparator having a first input receiving a corresponding phase clamp voltage and a second input receiving the neutral point clamp voltage. The U-phase comparison circuit, the V-phase comparison circuit, and the W-phase comparison circuit each include
a neutral point voltage dividing circuit that divides the neutral point clamp voltage;
a phase voltage divider circuit for dividing a clamp voltage of a corresponding phase;
a voltage comparator having a first input for receiving the output voltage of the phase voltage divider circuit and a second input for receiving the output voltage of the neutral point voltage divider circuit;
4. The motor driver circuit according to claim 1, comprising: The motor driver circuit of claim 8, wherein the phase voltage divider circuit is shared by the U-phase comparison circuit, the V-phase comparison circuit, and the W-phase comparison circuit. A motor driver circuit according to any one of claims 1 to 8, which is integrated on a single semiconductor substrate. The motor driver circuit of claim 10, wherein the three-phase inverter circuit is configured using discrete elements outside the motor driver circuit. The motor driver circuit of claim 10 further comprising the three-phase inverter circuit. A three-phase DC motor;
a three-phase inverter circuit connected to the three-phase DC motor;
A motor driver circuit according to claim 11, which controls the three-phase inverter circuit;
An electronic device comprising: A three-phase DC motor;
A motor driver circuit according to claim 12 for driving the three-phase inverter circuit;
An electronic device comprising:

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