JP4217052B2 - Motor drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a single-phase full-wave drive type motor drive circuit for rotationally driving a brushless motor.
[0002]
[Prior art]
As a driving method of a single-phase full-wave brushless fan motor, the rotational position of the rotor to which the permanent magnet is fixed is detected by a hall element, and the detection voltage output from the hall element is amplified and supplied to the stator coil of the motor. The method is used. In addition, the motor drive signal slew rate (driving per unit time) is used to reduce noise (suppression of rotational noise) and to suppress flyback voltage (voltage generated by the coil inductance component when the current flowing through the stator coil is reversed). A so-called soft switching drive system in which the signal change amount) is reduced is used. As an example of the prior art, a method disclosed in Japanese Patent Application No. 2001-128804 is used.
[0003]
FIG. 3 shows a motor driving circuit of the soft switching driving system described in the above specification. In FIG. 3, reference numerals 21 and 22 denote push-pull output operational amplifiers, and a stator coil of the brushless fan motor 23 is connected between their output terminals. A common connection point between the inverting input terminal (−) of the operational amplifier 21 and the non-inverting input terminal (+) of the operational amplifier 22, and the non-inverting input terminal (+) of the operational amplifier 21 and the inverting input terminal (−) of the operational amplifier 22. Hall element 24 is connected to the common connection point. A feedback resistor 25 (resistance value RF) is provided between the inverting input terminal (−) and the output terminal of the operational amplifier 21, and a feedback resistor 26 (between the inverting input terminal (−) and the output terminal of the operational amplifier 22. Resistance values RF) are respectively connected. Reference numerals 27 and 28 denote bias resistors of the Hall element.
[0004]
Here, in the motor drive circuit shown in FIG. 3, the Hall element 24 is equivalently represented by a signal source 24a that outputs voltages VH1 and VH2 (usually sine waves and opposite phases) and an output resistance value RH. Is shown in FIG. The operational amplifiers 21 and 22 constitute inverting amplifiers in which RH is an input resistance value and RF is a resistance value of feedback resistors 25 and 26, respectively. Since the operational amplifiers 21 and 22 output voltages obtained by multiplying the output voltages VH1 and VH2 of the Hall element 24 by “−RF / RH”, respectively, by setting the closed loop voltage gain to an appropriate value, the pseudo trapezoid can be obtained from the sine wave waveform. Soft switching drive with reduced slew rate by converting the waveform into a wave is realized.
[0005]
As described above, in the motor drive circuit shown in FIG. 3, the slew rate of the drive signal is determined by the ratio of the amplitude A of the output voltages VH1 and VH2 of the Hall element 24 to the output resistance value RH of the Hall element 24 and the feedback resistance value RF. The closed-loop voltage gain determined by When the operating frequency of the motor drive circuit is f and the time is t, the magnitude of the slew rate | SR |
| SR | = 2πfA | cos2πft | × (RF / RH) (1)
It can be expressed as.
[0006]
[Problems to be solved by the invention]
However, variations in voltage amplitude A and variations in voltage gain due to variations in resistance values RH and RF have caused variations in slew rate | SR |. That is, from the above equation (1), there are four types of parameters, A, RF, RH, and f, that determine the slew rate | SR |. Therefore, the slew rate | SR | was there.
[0007]
Here, a specific example of the slew rate | SR | when the operational amplifiers 21 and 22 and the feedback resistors 25 and 26 of FIG. 3 are formed of a semiconductor integrated circuit is shown. When an indium antimony type Hall element 24 is used for constant current bias, the output voltage amplitude A of the Hall element 24 has a variation of about ± 40%, and the output resistance value RH has a variation of about ± 30%. Yes. The feedback resistance value RF generally has a variation of about ± 30% when it is formed of a diffusion layer or polysilicon in the semiconductor integrated circuit manufacturing process. Therefore, when the variation of the slew rate | SR | is calculated from the equation (1), it can be seen that it has a range of −68% to + 160%. Further, since A, RF, and RH each have temperature characteristics, the fluctuation range of the slew rate | SR | further increases.
[0008]
The starting torque when the brushless fan motor is turned on is generally determined by the magnitude of the magnetic field generated by the current flowing in the stator coil and the magnitude of the magnetic field generated by the permanent magnet fixed to the rotor. It is necessary to generate a sufficient torque for starting. In the conventional soft switching drive system, the coil current, which is an element for determining the starting torque, includes the output voltages VH1 and VH2 of the Hall element at the stop position of the rotor, and the closed loop voltages of the operational amplifiers 21 and 22 expressed by RF / RH. It is determined by the gain and the offset voltage of the operational amplifiers 21 and 22. Since these variations lead to variations in coil current, that is, starting torque, it is necessary to design in such a way that no starting failure occurs in consideration thereof. From the above, conventionally, it has been necessary to ensure a large design margin for the motor drive circuit.
[0009]
The present invention is intended to improve the above problems, and provides a motor drive circuit that reduces variations in the slew rate of a motor drive signal and does not require a large design margin for obtaining a starting torque. Objective.
[0010]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a magnetic detection element for detecting a magnetic flux distribution of a rotor of a brushless motor and an in-phase output and / or an anti-phase output of the magnetic detection element, and a full swing in a power supply voltage range. A pulse generation means for outputting a rectangular wave, an integration circuit for integrating the output of the pulse generation means to output a trapezoidal wave signal, and an in-phase amplification section for amplifying and outputting the voltage output of the integration circuit in positive phase , and a reverse phase amplifier for outputting the reversed phase amplifies the voltage output of the integrating circuit, supplied with each voltage output of the in-phase amplifier section and opposite phase amplifier unit across the stator coils of the brushless motor the motor drive circuit, the integrating circuit includes an operational amplifier, a feedback capacitor C1 inverting input terminal and connected between the output terminal of the operational amplifier, the pulse generating means and said inverting input terminal An input resistor R3 connected to the power terminal and a voltage source of the voltage Vref connected to the non-inverting input terminal of the operational amplifier. The peak voltage of the rectangular wave is Vp, and Vref = Vp / 2. In this case, the motor drive circuit is characterized in that the slew rate | SR | is set as | SR | = (Vp / 2) / (C1 · R3) .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a brushless fan motor drive circuit according to one embodiment of the present invention, and FIG. 2 is a waveform diagram of its operation. Reference numeral 11 denotes a comparator (pulse generating means), which has an output voltage VH1 of one polarity and an output voltage of the other polarity of a Hall element (magnetic detection element) 14 biased by resistors 12, 13 (resistance values R1, R2). VH2 is input to the inverting input terminal (−) and the non-inverting input terminal (+), amplified, and converted into a rectangular wave that fully swings within the power supply voltage range. The output voltage of the comparator 11 is input to the integrating circuit 15.
[0014]
The integrating circuit 15 includes an operational amplifier 151, an input resistor 152 (resistance value R3) connected to the inverting input terminal (−) of the operational amplifier 151, an inverting input terminal (−) and an output terminal of the operational amplifier 151. And a voltage source 154 whose voltage is Vref connected to the non-inverting input terminal (+) of the operational amplifier 151, and the output of the comparator 11 is connected to the feedback capacitor 153 (capacitance value C1). A voltage obtained by integrating the time with Vref as a reference voltage is output.
[0015]
Reference numeral 16 denotes a non-inverting power amplifier (in-phase amplifier) composed of a differential amplifier circuit having a push-pull output that inputs the output voltage of the integrating circuit 15 to a non-inverting input terminal and amplifies the power in phase, and 17 denotes an output of the integrating circuit 15. This is an inverting power amplifier (anti-phase amplification unit) composed of a differential amplifier of push-pull output that inputs voltage to an inverting input terminal and amplifies power in the opposite phase, and a brushless fan motor between the output terminals of these power amplifiers Eighteen stator coils are connected.
[0016]
The rise / fall time in the soft switching operation takes a value of several to 10% of one cycle of the drive signal, and the slew rate required for this is 0.01 to 0.1 V / μsec. This value is as small as 1/10 to 1/100 or less of the slew rate of a general-purpose operational amplifier IC. Although this slew rate can also be used as a phase compensation circuit unit of the comparator 11 on the circuit, it is not practical when incorporated in an IC because the available capacitor is small.
[0017]
Therefore, in this embodiment, the integration circuit 15 that can set a large time constant is used, and a slew rate that is suitable for soft switching drive and has little variation is set here. In this integration circuit 15, when the peak voltage of the rectangular wave output from the comparator 11 is Vp, when Vref = Vp / 2, the slew rate | SR | of the output voltage of the integration circuit 15 is
| SR | = (Vp / 2) / (C1 · R3) (2)
Given in.
[0018]
Here, a specific example of variation in the slew rate | SR | when the comparator 11, the integration circuit 15, and the power amplifiers 16 and 17 of FIG. 1 are formed of a semiconductor integrated circuit is shown. From equation (2), there are three types of variation elements: Vp, C1, and R3. Vp is substantially equal to the power supply voltage if the output stage of the comparator 11 has sufficient current supply capability to drive the resistor 152 (R3), and its variation is substantially zero. The feedback capacitance value C1 is formed by a combination of polysilicon and silicon substrate, polysilicon and polysilicon, etc., but generally has a variation of about ± 10%. The resistance value R3 is formed by polysilicon, a silicon substrate, a diffusion layer, or the like, but generally has a variation of about ± 30%.
[0019]
From the above, when the variation of the slew rate | SR | is calculated from the equation (2), the variation is in the range of −31% to + 59%, which can be suppressed to about half or less of the conventional one. Further considering the temperature characteristics, the output voltage amplitude A of the Hall element, the output resistance value RH of the Hall element, and the feedback resistance value RF have temperature characteristics in the past, and these are due to variations in the slew rate | SR | On the other hand, in this embodiment, only the resistance value R3 has temperature characteristics, and variations due to temperature characteristics can be reduced.
[0020]
Further, in the conventional motor drive circuit, it is necessary to increase the design margin so as not to cause a start-up failure in consideration of variations in the offset voltages of the operational amplifiers 21 and 22 and VH1, VH2, RF, and RH in FIG. However, in this embodiment, after the output voltage of the Hall element 14 is converted into a rectangular wave that fully swings in the power supply voltage range by the comparator 11, the slew rate is converted by the integrating circuit 15 and the push-pull output is converted. The power amplifiers 16 and 17 amplify the power and supply the current to the stator coil of the motor 18, so that the maximum starting current, that is, the maximum starting torque can be generated, and the variation is small, so that the design margin is increased. There is no need to make it bigger.
[0021]
In the embodiment described above, voltages VH1 and VH2 of both polarities of the Hall element 14 are input and shaped into a rectangular wave by the comparator 11, but only one of the voltages VH1 and VH2 is shaped into a rectangular wave. Then, this may be integrated by the integrating circuit 15 and converted into a trapezoidal wave having a slew rate suitable for soft switching drive. The motor to be driven is not limited to a fan motor as long as it is a brushless motor using a magnetic detection element.
[0022]
【The invention's effect】
As described above, according to the first and second aspects of the present invention, when the brushless motor is driven by soft switching, the range of variation in the slew rate of the motor drive signal is conventionally large from −68% to + 160%. On the other hand, the variation range can be greatly reduced. In particular, according to the invention of claim 3, it can be suppressed to a small variation range of −31% to + 59%, which is less than half. Further, it is possible to generate the maximum starting torque at the time of starting, and it is not necessary to increase the design margin because the variation range is small.
[Brief description of the drawings]
FIG. 1 is a block diagram of a motor drive circuit according to an embodiment of the present invention.
FIG. 2 is a waveform diagram of the operation of the motor drive circuit of FIG.
FIG. 3 is a block diagram of a conventional motor drive circuit.
4 is an equivalent circuit diagram of the motor drive circuit of FIG. 3;
[Explanation of symbols]
11: Comparator 12, 13: Bias resistor 14: Hall element (magnetic detection element)
15: integration circuit, 151: operational amplifier, 152: input resistance, 153: feedback capacitor, 154: voltage source 16: in-phase power amplifier (in-phase amplifier)
17: Antiphase power amplifier (antiphase amplifier)
18: Brushless fan motor

Claims (1)

Magnetic detection element that detects the magnetic flux distribution of the rotor of a brushless motor, and pulse generation that outputs a rectangular wave that fully swings in the power supply voltage range by inputting the same phase output and / or opposite phase output of the magnetic detection element Means, an integration circuit that integrates the output of the pulse generation means to output a trapezoidal wave signal, an in-phase amplification unit that amplifies and outputs the voltage output of the integration circuit in the positive phase, and a voltage output of the integration circuit. In a motor drive circuit comprising a reverse phase amplification unit for performing reverse phase amplification and outputting, and supplying each voltage output of the in-phase amplification unit and the reverse phase amplification unit between both ends of the stator coil of the brushless motor,
The integrating circuit includes an operational amplifier, a feedback capacitor C1 connected between the inverting input terminal and the output terminal of the operational amplifier, and an input connected between the inverting input terminal and the output terminal of the pulse generating means. The resistor R3 and a voltage source of the voltage Vref connected to the non-inverting input terminal of the operational amplifier. When the peak voltage of the rectangular wave is Vp and Vref = Vp / 2, the slew rate | SR |
| SR | = (Vp / 2) / (C1 · R3)
A motor drive circuit characterized by being set in (1 ).

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