JP2004350461A - Inductive load driving device and vacuum cleaner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress noise, by reducing a large transient voltage that is caused to occur because of the inductivity of a load at the time of switching. <P>SOLUTION: With regard to the structure of a high-voltage-side driving circuit portion 4a, the circuit is structured by connecting a second resistance element 15 with a first resistance element 14 and the collector-emitter path of a first transistor 11 in series between a power supply terminal Pb of a second power source 7 and a ground terminal Pe, by connecting a third resistance element 16 with the collector-emitter path of a second transistor 12 in series between the connection point 18 of a first NchFET 3a and a second NchFET 3d connected in series and the power supply terminal Pb of the second power source 7, and by connecting the anode of a diode 13 and the gate of the first NchFET 3a to the connection point 20 of the second transistor 12 and the third resistance element 16. This circuit structure reduces the transient voltage that is generated when the second NchFET 3d at the low-voltage side is turned off so that the noise can be suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an inductive load driving device and a vacuum cleaner having the inductive load driving device.
[0002]
[Prior art]
FIG. 9 is a circuit diagram showing a high-voltage side driving circuit 100 of a conventional brushless motor driving device disclosed in Patent Document 1, for example. The high-voltage drive circuit 100 includes a bootstrap diode 101, a bootstrap capacitor 102, transistors 103 and 104, resistance elements 105 and 106, a diode 107, and the like.
[0003]
In the high-voltage drive circuit 100, when the low-voltage NchFET (N-channel field effect transistor; the same applies hereinafter) 108 of the brushless motor is on, the bootstrap capacitor 102 is charged via the bootstrap diode 101. You. The high voltage side NchFET 109 is turned on by this charging voltage.
[0004]
[Patent Document 1]
JP-A-5-328792
[Problems to be solved by the invention]
FIG. 10 shows a voltage waveform between the gate and the source of the high voltage side NchFET 109 when the brushless motor is rotationally driven using the conventional high voltage side driving circuit 100 shown in FIG. As can be seen from FIG. 10, at the moment when the low-voltage side NchFET 108 is turned off, a large transient voltage Vm is generated at the connection point 110 between the NchFET 109 and the NchFET 108 due to the inductive property of the brushless motor (winding). Such a large transient voltage causes noise in the circuit system.
[0006]
When the low voltage side NchFET 108 is turned off, the gate potential of the high voltage side NchFET 109 is the ground potential. As a result, a negative transient voltage Vm is generated between the gate and the source of the NchFET 109 as shown in FIG. . Therefore, if the transient voltage Vm is larger than the gate-source breakdown voltage ± Vp of the high-voltage side NchFET 109, the NchFET 109 is destroyed.
[0007]
Therefore, an object of the present invention is to reduce a large transient voltage generated due to load inductiveness at the time of switching and suppress noise.
[0008]
Another object of the present invention is to prevent generation of a transient voltage larger than the gate-source breakdown voltage of the high-voltage side NchFET.
[0009]
[Means for Solving the Problems]
The present invention relates to a plurality of first NchFETs provided on a high potential side of an inductive load (for example, a brushless motor), and a plurality of second NchFETs respectively connected in series to the first NchFET and provided on a low potential side of the inductive load. A high-voltage drive circuit for driving the first NchFET; an inductive load control unit for controlling the high-voltage drive circuit; a first power supply for supplying power to the inductive load; A second power supply that supplies power to the drive circuit unit, wherein the high-voltage-side drive circuit unit includes at least a first transistor, a second transistor, a diode, a first resistance element, and a second power supply. A resistance element and a third resistance element, wherein the first resistance element and the first transistor are connected between a power supply terminal of the second power supply and a ground terminal of the inductive load driving device. A collector-emitter path and the second resistance element are connected in series, a base of the first transistor is connected to an output terminal of the inductive load control unit, and the first NchFET and the second NchFET connected in series are connected. A collector / emitter path of the second transistor and the third resistance element are connected in series between a connection point and a power terminal of the second power supply, and a connection between the first resistance element and the first transistor is provided. A point is connected to a base of the second transistor and a cathode of the diode, and a connection point between the second transistor and the third resistance element is connected to an anode of the diode and a gate of the first NchFET.
[0010]
Accordingly, with respect to the configuration of the high-voltage side drive circuit section, the second transistor and the third resistor are used in addition to the first transistor, the second transistor, the diode, and the first resistor. A second resistor element is connected in series between the first resistor element and the collector-emitter path of the first transistor between the first resistor element and the ground terminal, and a connection point of the first NchFET / second NchFET connected in series and the second power supply are connected. A third resistor is connected in series between the power supply terminal and the collector-emitter path of the second transistor, and a connection point between the second transistor and the third resistor is connected to an anode of a diode and a first NchFET. Large transient voltage generated when the second NchFET on the low voltage side is turned off is reduced, thereby suppressing noise. It becomes possible to.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to FIGS.
[0012]
First, FIG. 1 shows a circuit diagram of an inductive load driving device 1 according to the present embodiment. A plurality of, for example, three first NchFETs 3a to 3c provided on the high potential side of the inductive load 2 having the windings 2a to 2c, and a plurality of, for example, three second NchFETs 3d provided on the low potential side of the inductive load 2 To 3f are connected in series. The output terminals of the high-voltage drive circuit units 4a to 4c and the low-voltage drive circuit units 4d to 4f are connected to the gates of the respective NchFETs 3a to 3f. Here, when turning on the first NchFETs 3a to 3c and the second NchFETs 3d to 3f, the high voltage side drive circuit units 4a to 4c and the low voltage side drive circuit units 4d to 4f apply a positive voltage to the sources of the respective NchFETs 3a to 3f. To the gates of the respective NchFETs 3a to 3f.
[0013]
Bootstrap circuits 5a to 5c are provided for the high voltage side drive circuit units 4a to 4c for driving the first Nch FETs 3a to 3c on the high voltage side, respectively. As a result, the high-voltage side drive circuit units 4a to 4c receive the supply of the driving DC power from the bootstrap capacitors 6a to 6c in each of the bootstrap circuits 5a to 5c.
[0014]
Here, the bootstrap circuits 5a to 5c include a driving power supply (second power supply) 7, bootstrap capacitors 6a to 6c, and a bootstrap diode connected between the power supply 7 and the bootstrap capacitors 6a to 6c, respectively. 8a to 8c and second NchFETs 3d to 3f. The inductive load control unit 17 turns off the first NchFETs 3a to 3c and turns on the second NchFETs 3d to 3f, thereby turning on the bootstrap circuits 5a to 5c. Then, the power supply 7 charges the bootstrap capacitors 6a to 6c via the bootstrap diodes 8a to 8c.
[0015]
Here, in the present embodiment, the high-voltage-side drive circuit units 4a to 4c include at least the first transistor 11, the second transistor 12, the diode 13, the first resistance element 14, the second resistance element 15, and the third resistance It is composed of an element 16 (in FIG. 1, only the inside of the high voltage side drive circuit section 4a is shown, but the same applies to the high voltage side drive circuit sections 4b and 4c).
[0016]
Next, the circuit configuration of the high voltage side drive circuit units 4a to 4c will be specifically described. A first resistor 14, a collector-emitter path of the first transistor 11, and a power supply terminal Pb (power supply terminal of the power supply 7) of the bootstrap circuit 51 a and a ground terminal Pe of the inductive load driving device 1. The second resistance element 15 is connected in series. Further, the base of the first transistor 11 and the output terminal Pa of the inductive load control unit 17 are connected. Further, a connection point 18 between the first NchFET 3a and the second NchFET 3d (the connection point 18 is connected to each of the windings 2a to 2c of the inductive load 2) and the power supply terminal Pb of the bootstrap circuit 5a. The collector-emitter path of the two transistors 12 and the third resistance element 16 are connected in series. The base of the second transistor 12 and the cathode of the diode 13 are connected to a connection point 19 between the first resistance element 14 and the first transistor 11. The anode of the diode 13 and the gate terminal Pc of the first NchFET 3a are connected to a connection point 20 between the second transistor 12 and the third resistance element 16.
[0017]
Reference numeral 21 denotes a power supply (first power supply) of, for example, about 30 to 40 V that supplies power to the inductive load 2 and the power supply 7.
[0018]
FIG. 2 shows a voltage waveform between the gate and the source of the high-voltage side NchFET 3a when the inductive load 2 is driven by using the high-voltage side drive circuit sections 4a to 4c having such a configuration. At this time, the voltage of the power supply 21 with respect to the inductive load 2 is 35V. A comparison between the circuit of the present embodiment and a conventional circuit has revealed that the transient voltage V1 generated when the low-voltage side NchFET 3d is turned off is small. The same applies to other phases.
[0019]
Thus, instead of the conventional circuit configuration in which the emitter side of the transistor 104 and one end of the resistance element 106 are directly grounded, a book including a configuration in which the second resistance element 15 is added and the connection of the third resistance element 16 is changed. By using the high voltage side drive circuit units 4a to 4c of the embodiment, a large transient voltage generated due to the inductive load 2 when the low voltage side NchFETs 3d to 3f are turned off is reduced, and noise is suppressed. It becomes possible.
[0020]
Next, the resistance value R2 of the second resistance element 15 will be described. FIG. 3 shows the values of the voltages V1 and V2 in FIG. 2 when the resistance values of the first resistance element 14 and the third resistance element 16 are fixed and the resistance value R2 of the second resistance element 15 is changed. Indicates a change. If the resistance value R2 is too small, the value of the voltage V1 exceeds the withstand voltage (± 20 V in this case) of the first NchFETs 3a to 3c. Conversely, if the resistance value R2 is too large, the value of the voltage V2 exceeds the gate threshold voltage (in this case, 2V) of the first NchFETs 3a to 3c. Therefore, the range of the resistance value R2 of the second resistance element 15 is defined by at least the voltage V1 and the voltage V2.
[0021]
Next, the resistance value R3 of the third resistance element 16 will be described. In FIG. 4, when the resistance values of the first resistance element 14 and the second resistance element 15 are fixed and the resistance value R3 of the third resistance element 16 is changed, the voltage V1 and the first NchFETs 3a to 3c in FIG. 3 shows the change in the loss P. If the resistance value R3 is too small, the value of the loss P exceeds the allowable loss (30 W in this case) of the first NchFETs 3a to 3c. Conversely, if the resistance value R3 is too large, the withstand voltage (in this case, ± 20 V) of the first NchFETs 3a to 3c will be exceeded. Therefore, the range of the resistance value R3 of the third resistance element 16 is defined by at least the allowable loss P and the voltage V1.
[0022]
As described above, by adjusting the resistance values R1, R2, and R3 of the first to third resistance elements 14, 15, and 16, the transient voltage V1 generated when the low-voltage-side NchFETs 3d to 3f are turned off can be reduced to the high-voltage side. The gate-source breakdown voltage of the FETs 3a to 3c can be reduced. In particular, in a device in which the power supply voltage of the inductive load 2 is higher than the gate-source withstand voltage of the first Nch FETs 3a to 3c on the high voltage side, and a device in which a larger current flows through the inductive load 2, the transient voltage V1 also increases. Therefore, this embodiment is effective.
[0023]
Next, a cordless type vacuum cleaner will be described as an electric device particularly suitable for using the inductive load driving device 1 of the present embodiment.
[0024]
FIG. 5 is a perspective view showing an external configuration of the vacuum cleaner 31 of the present embodiment. The vacuum cleaner 31 according to the present embodiment includes a housing 32 serving as a base, a hose 33 having one end detachably connected to the housing 32, a hand operation unit 34 provided at the other end of the hose 33, and one end. An extension pipe 35 having a two-part structure detachably connected to the hand operation unit 34, a suction port body 36 detachably attached to the other end of the extension pipe 35, and a fan motor 37 housed and held in the housing 32 ( 7), a dust collection chamber (not shown) formed in the housing 32, and the like.
[0025]
The hose 33 is connected to the housing 32 such that a base end thereof communicates with a suction side of a fan motor 37 via a dust collection chamber (not shown). A hand operation unit 34 provided at the other end of the hose 33 is provided. Is provided with a grip portion 38 extending rearward and operating means 39 located in a range operable by a finger of an operator holding the grip portion 38.
[0026]
The operating means 39 also serves as a power switch for the fan motor 37, and is configured to be able to select a plurality of types of operation modes for setting the fan motor 37 in different driving states. Specifically, as shown in FIG. 7, a stop operation button 39a for setting the operation mode to the stop state and a weak operation operation button for setting the operation mode to the weak operation state, as shown in FIG. 39b, a strong driving operation button 39c for setting the driving mode to a strong driving state is arranged in a line.
[0027]
7, the fan motor 37 includes a brushless motor 40 as the inductive load 2, and a centrifugal fan 41 driven to rotate by the brushless motor 40. FIG. 6 is a schematic diagram showing the shape of the impeller 42 of the centrifugal fan 41. The centrifugal fan 41 has been widely used since it has excellent performance for vacuum cleaners. The impeller 42 is fixed to a rotating shaft 44 of a rotor 43 surrounded by a yoke (not shown) of the brushless motor 40, and includes a main plate 45, side plates 46, and a plurality of blades 47. The blade 47 is provided with a plurality of convex portions, which are fitted into holes provided in the main plate 45 and the side plate 46 and are caulked to fix each. In the vacuum cleaner 31, the impeller 42 is rotated to 30,000 rpm or more to obtain a suction force.
[0028]
Next, a vacuum cleaner control device (fan motor drive device) 51 that drives the fan motor 37 of the vacuum cleaner 31 according to the present embodiment will be described with reference to FIG. The vacuum cleaner control device 49 rotationally drives the fan motor 37 including the brushless motor 40 (the inductive load 2) by an AC current generated from an inverter circuit 52 driven by the power source 21 having a battery configuration as a driving source. Here, the configuration of the vacuum cleaner control device (fan motor drive device) 51 including the inverter circuit 52 and the like basically conforms to the configuration of the inductive load drive device 1 described with reference to FIG. Yes, corresponding parts are indicated using the same reference numerals.
[0029]
That is, the inductive load control unit 17 is used for a vacuum cleaner and is configured as a vacuum cleaner control unit. Specifically, the inductive load control unit 17 includes a motor control unit 53, a main body control unit 54, a memory 55, and the like. The unit 56 is connected. The configuration of each of the NchFETs 3a to 3f and the drive circuit units 4a to 4f is the same as that of FIG. 1, but here, a resistance element 57 for adjustment is added in the high-voltage drive circuit units 4a to 4c. In addition, a transistor 58 for inverting a signal is added to the output of the vacuum cleaner controller 17.
[0030]
As the power source 21, an assembled battery in which a plurality of secondary batteries such as a nickel cadmium (NiCd) battery, a nickel hydride battery, and a lithium ion battery are combined is used. This DC voltage is supplied to the inverter circuit 52. The inverter circuit 52 has a configuration in which six NchFETs 3a to 3f are connected in a three-phase bridge, and based on a pulse signal output by the vacuum cleaner control unit 17 mainly including a microcomputer, the high voltage side drive circuit unit 4a To 4c and the low voltage side drive circuit units 4d to 4f to supply an alternating current to the windings 2a to 2c of the fan motor 37.
[0031]
In addition, the electric vacuum cleaner control device 51 includes an inverter circuit current detecting means 59 for detecting a current flowing through the inverter circuit 52 and an inverter circuit input voltage detecting means 60 for detecting an input voltage to the inverter circuit 52. Connected to the machine control unit 17. The state of the vacuum cleaner 31 is monitored by these detecting means 59 and 60. Further, a display unit 56 such as a garbage sign or a charge sign is connected.
[0032]
Further, the brushless motor 40 includes position detecting means 61 for detecting the position of the permanent magnet of the rotor 43. As such position detecting means 61, three magnetic sensors installed at an electrical angle of 120 ° are used. Examples of the magnetic sensor include a hall sensor and a hall IC. As an example of the relationship between the position detecting means 61 and the states of the NchFETs 3a to 3f, a switching pattern of a 120-degree conduction method is shown in FIG. The position detection means 61 outputs position detection signals 1, 2, 3 according to the permanent magnets arranged at regular intervals of the rotor 43. Then, the microcomputer of the vacuum cleaner control unit 17 outputs a pulse signal to the high voltage side drive circuit units 4a to 4c and the low voltage side drive circuit units 4d to 4f using the position detection signals 1, 2 and 3. Then, the NchFETs 3a to 3f are sequentially switched to supply a current to the windings 2a to 2c of each phase of the brushless motor 40 to generate torque. As other methods for detecting the position of the permanent magnet, although not particularly shown, a method using an optical pulse encoder, a method of detecting a voltage induced in the windings 2a to 2c by a voltage phase detecting means, and the like can be used. is there.
[0033]
Further, it is also possible to calculate the rotation speed of the rotor 43 using the above-described position detection signal. The rotational speed of the rotor 43 can be monitored based on the rotational speed. If an abnormal rotation speed is detected, the vacuum cleaner control unit 17 may stop the rotation of the rotor 43.
[0034]
In the 120-degree conduction method shown in FIG. 8, since there is a 60-degree non-conduction period between the on-period of the first NchFETs 3a to 3c and the on-period of the second NchFETs 3d to 3f in each phase, trouble such as dead band control is troublesome. No settings are required. Further, it is possible to easily control the rotation of the fan motor 37 using a simple position detecting means. Therefore, it is particularly useful in applications such as the fan motor 37 of the vacuum cleaner 31 in which the required rotation speed is as high as 30000 rpm or more and the switching of the NchFETs 3a to 3f is performed at high speed.
[0035]
In a cordless type vacuum cleaner equipped with an assembled battery in which a plurality of secondary batteries are combined, the voltage of the assembled battery is increased (around 30 V) in order to improve the dust suction force. Therefore, in that case, the voltage becomes higher than the gate-source voltage (for example, ± 20 V) of the first NchFETs 3a to 38c used on the high voltage side. Therefore, by applying the present embodiment, it is possible to reduce the value of the peak voltage generated at the time of switching, which is very effective for the above-described cordless type vacuum cleaner. .
[0036]
【The invention's effect】
According to the present invention, a large transient voltage generated at the time of switching when an inductive load is used can be reduced.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an inductive load driving device according to an embodiment of the present invention.
FIG. 2 is a time chart showing operating states of a first NchFET and a second NchFET and a voltage waveform between a source and a gate of the first NchFET.
FIG. 3 is a characteristic diagram illustrating a relationship between voltages V1 and V2 and a resistance value R2 of a second resistance element.
FIG. 4 is a characteristic diagram illustrating a relationship between a voltage V1, a loss of a first NchFET, and a resistance value R3 of a third resistance element.
FIG. 5 is a perspective view showing an external configuration of the vacuum cleaner.
6A and 6B schematically show an impeller of a centrifugal fan, wherein FIG. 6A is a front view, and FIG. 6B is a sectional view taken along line AA.
FIG. 7 is a circuit diagram showing a vacuum cleaner driving device.
FIG. 8 is an explanatory diagram showing a relationship between a position detection signal and operation states of first and second NchFETs.
FIG. 9 is a circuit configuration diagram showing a conventional example.
FIG. 10 is a time chart showing an operation state of a high-side NchFET and a low-side NchFET and a voltage waveform between a source and a gate of the high-side NchFET, showing a conventional example.
[Explanation of symbols]
2 Inductive loads 3a to 3c First NchFET
3d-3f 2nd NchFET
4a-4c High voltage side drive circuit section 4d-4f Low voltage side drive circuit section 7 Second power supply 11 First transistor 12 Second transistor 13 Diode 14 First resistance element 15 Second resistance element 16 Third resistance element 17 Inductive Load controller 18, 19, 20 Connection point 21 First power supply 30 Brushless motor (inductive load)
32 Housing 37 Fan motor 51 Fan motor drive

Claims (5)

A plurality of first NchFETs provided on the high potential side of the inductive load, a plurality of second NchFETs each connected in series to the first NchFET and provided on the low potential side of the inductive load, and a high voltage side for driving the first NchFET A drive circuit unit, an inductive load control unit for controlling the high voltage side drive circuit unit, a first power supply for supplying power to the inductive load, and a second power supply for supplying power to the high voltage side drive circuit unit A power supply, comprising:
The high-voltage side drive circuit unit includes at least a first transistor, a second transistor, a diode, a first resistor, a second resistor, and a third resistor.
Connecting the first resistance element, the collector-emitter path of the first transistor, and the second resistance element in series between a power terminal of the second power supply and a ground terminal of the inductive load driving device;
Connecting a base of the first transistor and an output terminal of the inductive load control unit,
A collector-emitter path of the second transistor and the third resistance element are connected in series between a connection point between the first NchFET and the second NchFET connected in series and a power supply terminal of the second power supply;
Connecting a base of the second transistor and a cathode of the diode to a connection point between the first resistance element and the first transistor;
An inductive load driving device, wherein an anode of the diode and a gate of the first NchFET are connected to a connection point between the second transistor and the third resistance element. 2. The inductive load driving device according to claim 1, wherein a voltage of the first power supply is higher than a source-gate breakdown voltage of the first NchFET. 2. The inductive load driving device according to claim 1, wherein the inductive load is a brushless motor. A housing to which the suction port body is connected,
A fan motor drive device having the inductive load drive device according to claim 3 housed in the housing;
An electric vacuum cleaner comprising: The vacuum cleaner according to claim 5, wherein the inductive load is a brushless motor having a three-phase structure, and is driven by a 120-degree conduction method.

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