JPH03285593A - Position detecting circuit for dc brushless motor - Google Patents

Abstract

PURPOSE:To generate an output voltage within an allowable range even when Hall elements, exhibiting fluctuation when being subjected to constant current driving, is employed by a method wherein a voltage dividing circuit is formed by connecting a resistor between the output terminals of the Hall element. CONSTITUTION:Resistors Ru, Rv, Rw, having the same resistance value R, are connected to the output voltage terminals of Hall elements Hu, Hv, Hw while the output voltage terminals are connected to an IC 10 for driving a motor. When the internal resistance of the Hall element is high and the output voltage is high, the dividing ratio of a voltage, divided by an internal resistor and an external resistor R, becomes small and a voltage inputted into the IC 10 for driving motor is contracted. When the internal resistance of the Hall element is low and the output voltage is low, the voltage dividing ratio between the internal resistor and the external resistor R is increased and the voltage, inputted into the IC 10 for driving the motor, is increased relatively. According to this method, the voltage, inputted into the IC 10 for driving the motor, is averaged inspite of the variety of the Hall element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the control of a DC brushless motor, and more particularly to a control circuit for controlling a DC brushless motor using a voltage-driven motor drive IC.

[Prior Art] A DC brushless motor rotates the rotor by applying a force to the permanent magnets of the rotor by supplying a current with a controlled phase to the coils of the stator.

Here, it is important to know the rotation angle of the rotor and supply current to the coil. A commonly used method for detecting the rotational angle (position) of the rotor is to place a Hall element near the rotor orbit and detect changes in the strength of the magnetic field formed by the permanent magnets of the rotor. A voltage-driven motor drive I that inputs such a voltage signal to control the flow of the motor drive.
C is often used.

Figure 2 shows a conventional DC brushless motor.
Three Hall elements Hu, Hv, H are used to detect the position (rotation angle) of the rotor, which indicates the connection of each part of the detection unit.
w is used. Each Hall element has a pair of current input terminals and a pair of voltage output terminals. The hall element is
Usually, a path for a current I is formed in a thin piece of semiconductor, a magnetic field with a magnetic flux density B is applied in the thickness direction of the thin piece, and a Hall voltage vH is generated in a direction perpendicular to I and B.

If the thickness of the thin section is t and the Hall constant is K), then the Hall voltage V) is expressed as VH = KHBI/l. Here, the Hall constant KH is inversely proportional to the carrier density. In the case of constant current drive, The Hall voltage is proportional to the magnetic flux density B and inversely proportional to the carrier density and thickness.Hall element H
For the sake of convenience, u, Hv, and Hw are connected in series as shown in the figure, and are supplied with a driving current from a power source of voltage Vs through resistors R1 and R2. Hall elements Hu, Hv,
The Hall voltage generated in Hw is supplied to the Hall voltage input terminal of the motor drive IC 10, and the respective operational amplifiers
It is increased by P1, O20, and oP3.

Based on the three Hall voltage signals obtained in this way, the motor drive ICl0 determines the position of the rotor of the brushless motor and supplies driving current to each coil.

[Problem to be solved by the invention] Generally, the specifications of a Hall element are a pair of! They are ranked based on the magnitude of the output voltage generated under a constant magnetic flux density when a constant voltage power source is connected to the current input terminal. In such a usage method, even if there are variations in the carrier density n or thickness t of the Hall element, the flowing current I is proportional to n and t, the Hall voltage VH is inversely proportional to n and t, and Since they are proportional, variations in n and t cancel each other out.

However, when multiple Hall elements are used in a connection as shown in Figure 2 (A>), constant current drive occurs, and variations in n and t directly appear in the output voltage.In this case, the current output of the Hall elements The voltage drop between terminals is not necessarily constant, so the performance of Hall elements grouped together under a constant voltage application will vary widely, and the input resistance of Hall elements may vary by more than ±50%. For this reason, which is not rare, if Hall elements with uniform output voltages are used in the connection shown in Figure 2 (A) under constant voltage drive conditions, the Hall voltage will vary by more than ±50%. .

In other words, the equivalent circuit of the output section of the Hall element is shown in Figure 2 (B
), the electromotive force e of the voltage generating part of the Hall element varies by more than ±50% from that voltage under constant current drive. However, if the input impedance of the operational amplifier is sufficiently larger than the internal resistance R)t, the voltage applied to the operational amplifier will be approximately e and will vary widely. In order to prevent variations, it is necessary to select the input resistance of the elements or to connect them in parallel and drive them at a constant voltage.

These measures result in increased costs and increased power supply current.

An object of the present invention is to provide a position detection circuit for a DC brushless motor that can generate an output voltage within the allowable range of a motor drive IC even when using a Hall element with variations when driven with a constant current. be.

[Means for Solving Problem 1] According to the conventional technology, a plurality of Hall elements with greatly different output voltages e were connected as they were to the motor drive IC, so variations in the output voltage were directly connected to the input signal of the motor drive IC. There was a variation in the number of

According to the present invention, as shown in FIG. 1(A), a plurality of Hall elements are connected in series f#, and resistors Ru, Rv, having a constant resistance value R, Rw
or connected.

If we show the equivalent circuit of the output part of such a Hall element, the first
In other words, the internal resistance RH-RH is connected to the voltage output e of the Hall element, the external resistance R is connected between both terminals, and the voltage between the terminals of the external resistance R (R /
(2RH1R))e is input to the motor drive IC. In this way, variations in the output voltage are reduced.

As described above, the output voltage e of the Hall element is inversely proportional to the carrier density and film thickness of the Hall element. Incidentally, factors such as carrier density and film thickness occur in both the output section of the Hall element and the current input section of the Hall element. When the carrier density is low and the film thickness is thin, the resistance between the current terminals is high, and a high output voltage is generated when driven with a constant current. At this time, the internal resistance RH of the output section is also large, and this large output resistance R
If we create a voltage divider circuit with H and a small resistor R"C" and output the voltage between the terminals of the resistor R, the output voltage will be small. Conversely, if the carrier density is high and the film thickness is thick, the internal resistance of the Hall element will be low, and the output voltage when driven with a constant current will be small, but the internal resistance RH of the output section will also be small. When a voltage dividing circuit is formed by externally connecting R, the voltage appearing across the resistor R becomes relatively large.

In this way, the magnitude of the output voltage of the Hall element is averaged by connecting a certain resistance between the output terminals.

Embodiment 3] The input portion of a position detection circuit for a DC brushless motor according to an embodiment of the present invention is a circuit as shown in FIG. 1(A). A plurality of Hall elements, three Hall elements Hu, Hv, and Hw in the illustrated case, are connected in series and driven with a constant current. That is, three Hall elements Hu, Hv,
Hw is connected. Resistors Ru, Rv, and Rw having the same resistance value R are connected to the output voltage terminals of these Hall elements, and the voltage between the terminals of these resistors Ru, Rv, and Rw is applied to the three input terminal pairs of the motor drive ICl0. and to the input terminals of the respective operational amplifiers OPI, OR2, and OR3. The value R of the resistance is selected to be approximately equal to the average value of the internal resistance 2R) of the output circuit of the Hall element.In other words, in the equivalent circuit shown in Fig. 1(B), the output voltage e is selected to be the most effective for the external R and R) (+
At this time, the input voltage input to the operational amplifier is (R/(2RH+R))e.

A more specific embodiment of the present invention is shown in FIG.

The motor drive ICl0 is the stator coil Lw of the motor.
-Terminals P2 and R for supplying driving current to Lv-Lu
8, pH. Currents supplied to these three-phase coils are supplied from the power supply line 2 through the resistor R9 from the bin P12. These three phase coils Lw-Lv-Lu
@ current supplied to three Hall elements Hw, Hv, Hu
It is controlled by a position detection signal formed by the Hall voltage supplied from the sensor. Hall elements Hw, Hv, and Hu are connected in series between power supply line 2 and ground line 1 via resistors R111 and R112. That is, the three Hall elements are driven with the same current.

The voltage output terminals of the Hall elements Hw, Hv, and Hu are short-circuited by resistors Rw, Rv, and Ru with a resistance value R, and these resistors Rw,
The voltages between the Rv and Ru terminals are R3-R4, R5-R6, and R9- of the Hall voltage input terminals of the motor drive IC, respectively.
10 is input. When the internal resistance of the Hall element is high and the output voltage is high, the voltage division ratio between the internal resistance and the external resistor R becomes small, and the voltage input to the motor driving RCIO is reduced. Compared to this, when the internal resistance of the Hall element is low and the output voltage is low, the voltage division ratio between the internal resistance and external resistor R becomes large, and the voltage input to the motor drive ICl0 becomes relatively large. . In this way, the voltage input to the motor drive IC is averaged, regardless of variations in the Hall elements.

Note that a resistor R7 and a capacitor C are connected between the coil Lw and the ground.
Similarly, a resistor R6 is connected between the coils Lv and Lu and the ground, and serves to absorb voltage changes when noise occurs in the coil Lw. and a capacitor C6 are connected in series, and a resistor R5 and a capacitor C5 are connected in series. Incidentally, capacitors C8 and C9 are connected between the phase compensation circuit terminal bin P15, the coil drive current flowing through the bin P12, and the power supply line, and together with R1 connected between the bin P15 and the ground, form a phase compensation circuit. are doing. The signal at the voltage output terminal of the Hall element Hw is connected to the resistor RIO
, capacitor C12, resistor R11, and capacitor C1
3, the AC components are respectively input to input terminals P23 and R22 of the rotation speed detector. Also,
The amplifier output of terminal P1 is connected to resistor R102 and capacitor C.
The signal is supplied to an integral signal input terminal P26 via an integrating circuit formed of l0I and ClO2.

Note that capacitors Cl01C1l are elements that determine the constant of the filter, capacitors C1 and 02 are capacitors for stabilizing the +12V power supply line, and capacitors C3 and C
4 is a capacitor for stabilizing the -i-5V power supply line. Switch 4 is a switch that instructs the motor to turn on and off. When this switch is turned on, the voltage at terminal 5 is set to ground potential, and when it is turned off, the potential at terminal 5 is set to ground potential.
2 to the 5v power supply. Pin P17 receives a clock signal from clock signal input terminal 7 via resistor R3.

The motor drive ICl0 can be configured with an IC called HA13476 available from Hitachi, Ltd., for example. In this case, the operating input voltage range of the Hall input is 60 to 200
mVp-p, and when considering changes in the power supply voltage, the variation in Hall output voltage must be suppressed to approximately 70 to 180 mV. Moreover, variations in the dimensions between the Hall element and the magnet, and the magnetic flux density of the magnet must be suppressed. Since there are variations in voltage, it is almost impossible to satisfy this voltage range by using general standard Hall elements available on the market without proper selection. In the circuit shown in FIG. 3, by connecting the output resistors Rw, Rv, and Ru, it is easy to keep the output standard of the Hall element within an allowable range without any special selection.

Therefore, costs required for selecting and managing Hall elements can be saved. Furthermore, compared to the case where Hall elements are driven in parallel, it is now possible to obtain stable output without using a large current.

Although the present invention has been described above in accordance with the examples, the present invention is not limited to these examples. For example, various modifications,
It will be obvious to those skilled in the art that improvements, combinations, etc. are possible.

[Effect of the invention] When supplying input to a plurality of standardized Hall input terminals using a plurality of Hall elements with varying performance,
It is possible to equalize the Hall signal voltage.

Therefore, various problems caused by variations in performance of Hall elements can be solved.

[Brief explanation of the drawing]

Fig. 1 shows the basic configuration of the present invention, Fig. 1 (A) is a circuit diagram showing connections, Fig. 1 (B) is a circuit diagram showing an equivalent circuit of the Hall element output section, Fig. 2 (A) , (B) are circuit diagrams showing a conventional technique corresponding to FIGS. 1(A) and (B), and FIG. 3 is a circuit diagram showing a motor drive circuit according to a more specific embodiment of the present invention. Ground line Power line Switch on/off signal terminal Motor drive IC Capacitor resistor Hall element coil IC pin

Claims (2)

[Claims] (1) A circuit for detecting the rotational position of a rotor of a DC brushless motor, comprising a plurality of Hall elements each having a current input terminal and a voltage output terminal, and for detecting a magnetic field formed by the rotor. A position detection circuit for a DC brushless motor, comprising: a resistor connected between output terminals of each of the Hall elements; and a plurality of amplifiers connected to the output terminals of the plurality of Hall elements and amplifying input voltage. (2) The D according to claim 1, wherein the resistor has a resistance value approximately equal to an average value of output resistances of the plurality of Hall elements.
C brushless motor position detection circuit.