JPS6217958B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brushless motor drive circuit,
In particular, the present invention relates to a drive circuit for a two-phase brushless motor having a pair of excitation coils.

A so-called brushless motor detects the rotation angle position of a magnetized rotor using a magnetically sensitive element such as a Hall element placed near the rotor, and operates a drive coil according to the detection result. The structure is such that the rotor is energized to provide rotational force to the rotor.

Here, among such brushless motors, a two-phase brushless motor is defined as one in which a pair of drive coils are arranged with an angular difference of about 90 degrees along the rotational direction of the rotor.

Here, one example of a conventional two-phase brushless motor drive circuit will be described with reference to FIG. In FIG. 1, transistors Q ₁₁ , Q ₁₂ and Q ₁₃ , Q ₁₄ each form a differential pair, one of the output terminals of the Hall element H ₁ is the base of the transistors Q ₁₁ and Q ₁₃ , and the other is the base of the transistor Q ₁₂ , connected to the base of Q ₁₄ . Although not shown, a predetermined bias voltage is supplied to the bias terminal of the Hall element. Therefore, the voltage between the output terminals of the Hall element _H1 changes according to the change in the density of the magnetic flux passing through the Hall element _H1 , and the current distribution in each differential pair changes accordingly. On the other hand, transistor Q ₂₁ ,
Q ₂₂ and transistors Q ₂₃ and Q ₂₄ also form a similar differential pair, and are formed so that the current distribution of each differential pair varies depending on the output voltage of the Hall element H ₂ . The sinking current sources of each differential pair are transistors Q ₁ , Q 2 , Q ₂ , biased by a predetermined voltage E ₁ .
It is composed of Q ₃ , Q ₄ and emitter resistors R ₁ , R ₂ , R ₃ , and R ₄ . Further, a current supply source to each differential pair is constituted by a B power supply and resistors R ₅ , R ₆ , R ₇ , and R ₈ . Therefore, changes in current distribution in each differential pair appear as changes in potential drops across resistors R ₅ , R ₆ , R ₇ , and R ₈ , and this is reflected in the operational amplifiers OP ₁ and OP _{2 .}
and OP ₃ and OP ₄ to increase the width of the drive coil L ₁ ,
_L2 is supplied to provide rotational force to the motor rotor.

In the above-mentioned conventional technology, due to variations in the characteristics of the resistors R ₁ to _{R 4} , the transistors Q ₁ to _{Q 4}
This causes variations in the sink current. This results in variations in the operating current of each differential pair, resulting in uneven rotation of the motor.

Therefore, it is an object of the present invention to provide a drive circuit for a two-phase brushless motor that does not have the above-mentioned problems in the prior art.

A drive circuit for a two-phase brushless motor according to the present invention connects in series a first differential pair consisting of NPN (or PNP) transistors and a second differential pair consisting of PNP (or NPN) transistors. While the differential pairs are driven by a single constant current source, different bias potentials are applied to the magnetically sensitive elements of the motor to cause the base potential of each differential pair to vary depending on the rotor position. The current change in each current path of each differential pair is derived by a current mirror circuit and supplied to the electromagnetic coil of the motor.

Examples of the present invention will be described in detail below.

FIG. 2 schematically shows a two-phase brushless motor and shows a specific circuit of a drive circuit according to the present invention for driving this brushless motor. In this figure, a rotor 1 of a two-phase brushless motor is magnetized so that an appropriate number of north poles and south poles are arranged alternately. H ₁ and H ₂ are subject to magnetic field changes due to the rotation of the rotor 1. Drive coil L ₁ , L ₂
is driven by a drive circuit to apply an appropriate rotational force to the rotor depending on the angular position of the rotor 1.

A drive circuit according to the present invention that drives a two-phase brushless motor having such a configuration uses an NPN transistor.
A first differential pair consisting of Q ₁₁ , Q ₁₂ and resistors R ₁₁ , R ₁₂ , PNP transistors Q ₂₁ , Q ₂₂ and resistors R ₂₁ , R ₂₂
and NPN and PNP transistors Q ₃₁ and Q ₃₂ whose bases are biased by a bias voltage Vb, and the emitter sides of the first and second differential pairs are coupled to each other. It includes a constant current circuit that supplies constant current to the pair. The bases of the transistors, which are the control terminals of the first and second differential pairs, are connected to the output terminals of the Hall elements H ₁ and H ₂ , respectively. Further, the bias terminals of one side of the Hall elements H ₁ and H ₂ are connected in series through a resistor R ₀ , and the power supply voltage +B is connected between the other bias terminals.
is supplied. Power supply voltage +B is resistor R ₁₃ ,
R ₁₄ and diode configuration transistors Q ₁₃ , Q ₁₄
is supplied between the collectors of the first and second differential pairs through a series circuit of resistors R ₂₃ , R ₂₄ and diode-configured transistors Q ₂₃ , Q ₂₄ to the current path of each differential pair. It supplies current. Transistor Q ₁₃ is connected to transistors Q ₁₅ , Q ₁₇ and resistor
Together with R ₁₅ and R ₁₇ they form a first current mirror circuit with two output terminals, and transistor Q ₁₄ forms a similar second current mirror circuit together with transistors Q ₁₆ and Q ₁₈ and resistors R ₁₆ and R ₁₈ . . transistor
Q ₂₅ , Q ₂₇ and resistors R ₂₅ , R ₂₇ and transistors
Q ₂₆ , Q ₂₈ and resistors R ₂₆ , R ₂₈ constitute third and fourth current mirror circuits, respectively. 1st and 3rd
The output terminals of one of the current mirror circuits are coupled together at a coupling point _P1 , and the output terminals of one of the second and fourth current mirror circuits are coupled together at a coupling point _P2 . Further, the other terminals of the first and fourth current mirror circuits are coupled together at a coupling point _P3 , and the other terminals of the second and third current mirror circuits are coupled together at a coupling point _P4 . The potential changes at these connection points P ₁ to P ₄ are
Amplified by the first to fourth emitter follower pairs consisting of Q ₄₁ , Q ₄₂ ; Q ₄₃ , Q ₄₄ ; Q ₄₅ , Q ₄₆ ; Q ₄₇ , Q ₄₈ , and driven by the first and second emitter follower pairs. The coil _L1 is excited, and the drive coil _L2 is excited by the third and fourth emitter follower pair.

In the drive circuit described above, when one of the magnetic poles of the rotor faces the Hall element _H1 , the Hall element
If a voltage develops across the output terminals of H ₁ and, for example, when transistor Q ₂₁ is on and transistor Q ₂₂ is off, the current flowing through transistor Q ₁₂ increases and the current flowing through transistor Q ₁₁ decreases, then the node P Since the potential at the node _P2 decreases and the potential at the node _P2 increases, a current flows in the drive coil _L1 from the transistor _Q43 to the transistor _Q42 . Hall element
When different magnetic poles face H ₁ , current flows in the coil L ₁ in the opposite direction. Similarly, when the magnetic pole faces the Hall element H ₂ , excitation currents in opposite directions alternately flow through the drive coil L ₂ .

In FIGS. 3A to 3D, Hall elements H ₁ , H ₂
2 shows waveforms showing changes in the output voltage of the drive coils L ₁ and the excitation current of the drive coils L 1 and L ₂ .

It is clear from the above that in the brushless motor drive circuit according to the present invention, two differential pairs are connected in series and current is supplied by a single constant current source. There are no problems such as uneven rotation due to variations.

Furthermore, since the current change in the differential pair is derived by a mirror circuit, a large dynamic range can be achieved.

Further, even if the power supply voltage +B varies with respect to the power supply E of the constant current circuit, the total current flowing through the differential pair does not change, so the excitation current is not affected, so the operation is stable.

Furthermore, by changing the base bias Vb of the transistors Q ₃₁ and Q ₃₂ of the constant current circuit, the current supplied to the first and second differential pairs can be increased or decreased, and the current supplied to the first and second differential pairs can be increased or _decreased . L ₂
By changing the amplitude of the excitation current flowing through the motor, speed control can be achieved. In this case, the circuit of transistors Q ₃₁ and Q ₃₂ and the power supply circuit work together as current supply means for speed control.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional brushless motor drive circuit, FIG. 2 is a circuit diagram showing a brushless motor drive circuit according to the present invention, and FIG. 3 is a circuit diagram showing a brushless motor drive circuit according to the present invention.
FIG. 3 is a diagram showing operating waveforms of the circuit shown in the figure. Explanation of symbols of main parts, 1...Motor rotor,
L ₁ , L ₂ ... Drive coil, H ₁ , H ₂ ... Hall element, Q ₁₁ , Q ₁₂ ... Transistors forming the first differential pair, Q ₂₁ , Q ₂₂ ... The second differential pair. Constituent transistors, _Q31 , _Q32 ...Transistors that compose the constant current circuit.

Claims (1)

[Claims] 1. A magnetized rotor, first and second magnetically sensitive elements disposed near the rotor, and a pair of drive coils disposed near the rotor. A drive circuit for a two-phase brushless motor consisting of a bias circuit that applies a predetermined bias voltage to each of the bias terminals of the magnetically sensitive element, and an NPN (or
a first differential pair consisting of a PNP (PNP) transistor and controlled by the output voltage of the first magnetically sensitive element; and a second differential pair consisting of a PNP (or NPN) transistor connected in series with the first differential pair. a second differential pair controlled by the output voltage of the magnetic element; a constant current supply circuit that supplies a predetermined current to the first and second differential pairs; and each of the first and second differential pairs. A drive circuit comprising: current mirror means for outputting a current proportional to a current flowing in a current path; and an excitation circuit for exciting the drive coil according to each output current of the current mirror means. 2. The current mirror means includes first and second current mirror circuits that output currents proportional to the currents flowing in each current path of the first differential pair, and currents flowing in each current path of the second differential pair. The excitation circuit is comprised of third and fourth current mirror circuits each outputting a current proportional to the current, and the excitation circuit is configured to supply a current to the drive coil according to a difference in output current of each of the current mirror circuits. A drive circuit according to claim 1, characterized in that: