JP3281837B2 - Fan motor control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fan motor control circuit for performing variable speed control of a DC brushless motor (hereinafter referred to as a motor) used for a fan or the like.

[0002]

2. Description of the Related Art DC brushless motor type fans are:
Since the control circuit is housed in a limited space, it is required to be small and to be realized at low cost. For this reason, a two-phase half-wave drive with an electrical angle of 180 degrees and a phase difference of switching the two output transistors by using one magnetic detection element to detect the rotor position and use this signal is generally adopted as a method with few circuit components. Have been.

A conventional variable speed control circuit for a motor of this type has a circuit configuration as disclosed in Japanese Patent Application Laid-Open No. 3-190588, for example. FIG. 2 is a typical circuit diagram of a conventional fan motor control circuit. As shown in the figure, the signal of the magnetic sensing element 3 is amplified by an amplifier 21 and is output via a distribution circuit 22 to two output transistors 23a,
23b, and the drive current is supplied to the two-phase motor coil 1a,
1b is energized. The amplifier 21 and the distribution circuit 22 are built in the motor drive control IC 4.

The speed command circuit 24 includes a rotation pulse generation circuit 25, a charging circuit 29 including a resistor 26, a capacitor 27 and a transistor 28, and a comparator 30. The speed switching means 31 operated by a signal from the rotation speed switching signal input terminal 36 is a transistor 32
And a resistor 33. The operation of this control circuit is as follows.

FIG. 3 is a timing chart for explaining the operation. As shown in the figure, (3-1) is the output voltage waveform of the amplifier 21, (3-2) and (3-3) are the output signals of the distribution circuit 22 at full speed, and (3-4) Is (3-
This is an output signal of the rotation pulse generation circuit 25 generated at the zero crossing of 1), and (3-5) is a voltage waveform of the capacitor 27 of the charging circuit 29. Here, the output signal of the rotation pulse generation circuit 25 conducts the transistor 28, extracts the charge of the capacitor 27, sets the voltage to 0, and thereafter,
The charging of the capacitor 27 starts, and the voltage rises linearly. When the voltage of the capacitor 27 reaches the reference voltage Vx divided by the resistors 34 and 35 by the charging circuit 29, the comparator 30 operates and outputs the signal shown in (3-6). Note that the resistor 33 in the speed switching means 31 sets the reference voltage Vx, and the transistor 32, which is operated by a signal from the rotation speed switching signal input terminal 36, is operated when the reference voltage Vx is close to the zero voltage value. .

The output signal (3-6) of the comparator 30 is connected to the distribution circuit 22, and the current is supplied to the transistor 23a.
23b to supply current to the motor coils 1a and 1b. As a result, currents as indicated by solid lines in (3-7) and (3-8) flow in each of the two phases, and the initial energization from the start of energization to a certain time is cut off. (3-7), (3
The dashed line -8) shows the coil current waveform at full speed.

Further, as shown in FIG. 4, the voltage applied to the DC motor 41 is dropped by a variable three-terminal regulator 42 in response to a speed command from a rotation speed switching signal input terminal 36 to reduce the rotation speed of the DC motor 41. There is a variable system (see JP-A-2-223395). If such a method is applied to a two-phase DC brushless motor having a phase difference of 180 degrees in electrical angle, a two-phase DC brushless motor can be driven by a circuit as shown in FIG.

[0008]

A fan used for cooling a copying machine or the like rotates at full speed during operation of the copying machine, and reduces noise and temperature rise of the fan during standby to reduce the length of the fan bearing. The speed is often reduced for the purpose of extending the life. When the motor is operated at a low speed, the wind noise generated by the blades of the fan is reduced, but the vibration and electromagnetic noise of the motor are emphasized, which causes discomfort.

Further, when two-phase half-wave driving with a phase difference of 180 degrees in electrical angle is performed by the conventional control circuit as described above, torque ripple which causes noise and circuit heat which deteriorates the bearing life are generated. There is a problem. The state of occurrence of this torque ripple will be described below.

FIG. 6 shows the torque generated by the motor during rotation at full speed. (6-1a) and (6-1b) show motor coils 1a, which are energized at an electrical angle of 180 degrees at full speed.
The back electromotive forces Ea and Eb induced in the motor coil 1b, and the motor coils 1a and 1b are obtained by subtracting the back electromotive forces Ea and Eb from the power supply voltage Vcc (Vcc-Ea) and (Vcc-Eb) as (6-2a). ),
Is applied as shown in (6-2b). (6-3
a) and (6-3b) are current waveforms Ia and Ib flowing through the motor coils 1a and 1b due to the applied voltage, and the rise of the current is delayed by the inductance components of the motor coils 1a and 1b. Since the rotation torque τ generated in the motor coils 1a and 1b is proportional to the product of the back electromotive force and the motor coil current, the rotation torque generated in the two-phase coil at full speed rotation has a shape like (6-4). . Also, (6-
5) is a coking torque generated by the positional relationship between the rotor magnet and the stator core of the motor, which determines the rotor stop position and ensures the start of the motor.
(6-6) is the motor torque that is the sum of the rotation torque and the coking torque. This motor torque (6-6) is not constant as shown in the figure, but includes torque ripple. Generally, the motor torque is designed to be a constant value to reduce vibration and noise of the motor.

However, in the above-described variable conduction angle method shown in FIG. 2, the current flowing through the two-phase coil during low-speed rotation is as shown in (7-1) and (7-2) of FIG. Is generated as shown in (7-3), the coking torque is the same as at full speed regardless of the number of rotations, and the motor torque which is the sum of the rotation torque and the coking torque is (7-4). become that way. By cutting off the initial stage of coil energization during low-speed rotation, the energization angle becomes 18
The range where the rotation torque of the two-phase coil is zero, which is not 0 degree, is widened, and the magnitude of the motor torque changes during one rotation of the motor, resulting in a large torque ripple. This torque ripple causes the vibration of the motor and is transmitted to the blades of the fan, which causes an increase in noise.

In the conventional regulator system shown in FIG. 5, the current waveform (7-
5), (7-6), rotation torque (7-7), and motor torque (7-8) are as shown in the figure, and the size of the motor torque ripple is smaller than in the variable conduction angle method.
However, the drop voltage of the three-terminal regulator at the time of low speed is a loss of the regulator circuit as a product of the flowing currents and generates heat. This not only significantly lowers the motor efficiency, but also has a problem that the bearing life of the fan is greatly affected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and does not reduce the efficiency even at a low speed.
Inexpensive circuit configuration reduces torque ripple and lowers motor noise.
Not only voltage but also PWM (pulse)
width modulation) It is an object of the present invention to provide a fan motor control circuit capable of changing a pulse duty.

[0014]

In order to achieve this object, according to the present invention, a current detecting resistor for detecting a current flowing through a motor coil as a voltage is compared with a voltage of the current detecting resistor and a rotation speed command voltage. A switching circuit for turning on / off a power supply voltage according to an output of the comparison circuit; and an energy stored in the motor coil when the switching circuit is on as a current when the switching circuit is off. the inner is circulated is provided and a current circulation circuit for release, capacitor to the power supply
Connect the other end of the capacitor to the other end of the capacitor.
Connect one terminal of the resistor to the other end of the resistor.
Is a buffer that converts the rotational speed command voltage into impedance
Connect to the circuit output and connect the resistor and the capacitor
Is connected to the input terminal of the comparison circuit,
The resistor and the capacitor are connected to the differentiation circuit when the motor starts.
And a PWM pulse is input to the rotation speed command terminal.
When it is input, it operates as a primary low-pass filter.

[0015]

In this case , when the motor is locked, the switching circuit may be forcibly turned on by an alarm signal output from the motor drive control IC.

[0017]

FIG. 1 is a diagram showing an embodiment of a control circuit for a fan motor according to the present invention. As shown in the figure, when a current having a phase difference of 180 degrees in electrical angle is applied to the two-phase motor coils 1a and 1b, a rotor including a permanent magnet (not shown) and a blade rotate.

An output signal of the magnetic detecting element 3 for detecting the position of the rotor is input to a motor drive control IC 4 including an amplifier and a distribution circuit, which is an energization command signal generation circuit. By turning on / off the two transistors 5a and 5b, a periodic current flows through the motor. The current flowing through the motor coils 1a and 1b is converted into a voltage value by a current detection resistor 9 and connected to a positive input terminal of a comparator (comparison circuit) 8, while a rotation speed command voltage input from a rotation speed command terminal 18 is provided. Reference numeral 18a is connected to the negative input terminal of the comparator 8 via the buffer circuit 7 and the resistor 13. The output section of the comparator 8 is an open collector of an output transistor (not shown). When the voltage of the current detection resistor 9 is smaller than the rotation speed command voltage 18a, the output transistor of the comparator 8 is turned on. The output of the comparator 8 is turned on by a switching circuit 19 including a PNP-type transistor 11 and base resistors 6 and 15,
The power supply voltage Vcc is applied to the motor coils 1a and 1b. Then, the current increases, and the voltage of the current detection resistor 9 increases. When the voltage exceeds the rotation speed command voltage 18a, the output transistor of the comparator 8 is turned off, and the transistor 1
1 is turned off, and no voltage is applied to the motor coils 1a and 1b.

When the transistor 11 is turned on, a current flows through the motor coils 1a and 1b,
b stores energy, but when the transistor 11 is turned off, a circulating current flows through the current circulating circuit 20 including the transistors 5a and 5b, the current detection resistor 9, the diode 12, and the motor coils 1a and 1b.
The stored energy is released. As described above, by turning on / off the transistor 11, the current of the motor coils 1a and 1b is controlled to a current value corresponding to the rotation speed command voltage 18a, as shown in (7-9) and (7-10) of FIG. It becomes a constant value without being affected by the motor induced voltage.

As a result, as described above, the motor torque during rotation is as shown in FIG. 7 (7-12), the torque ripple becomes very small, and the motor vibration is reduced.

FIG. 9 shows the state at the moment when the power supply voltage Vcc is applied. In FIG. 9, (9-1) is the voltage value of the power supply in the circuit, and (9-2) Is the capacitor 14
A voltage waveform obtained by a differentiating circuit of the comparator 13 and the resistor 13. The voltage of the negative input terminal of the comparator 8 rises to a value equal to or higher than the full-speed rotation command voltage for a short time. The same phenomenon occurs even when the low-speed rotation command is set to a low voltage value, and the starting torque of the motor is the same as at full speed, and the motor can be started reliably.

When the fan is mechanically locked, an alarm signal (8-2) shown in FIG. 8 is generated from the motor drive control IC 4, the transistor 10 is turned on, and the transistor 11 is unrelated to the comparator 8. At the same time, a starting torque similar to that at the time of full speed is generated, and starting can be surely performed.

FIG. 9 (9-3) shows a case where the rotational speed command value is supplied not by a DC voltage but by a PWM pulse of a certain frequency from a microcomputer or the like. It operates as a primary low-pass filter, and the negative input terminal of the comparator 8 is converted into a DC voltage as shown in (9-4), and the operation is the same as that in the case where the rotational speed command is a DC voltage.

In the above-described configuration, the motor coil 1a, the motor coil 1a,
When the current flowing through 1b is large, the switching circuit 19 is turned off by the comparison circuit 8. At this time, the energy stored in the motor coils 1a and 1b while the switching circuit 19 is on is circulated and released as current by the circulation circuit 20 in the motor coils 1a and 1b, and the motor coil current is attenuated. When the motor coil current value falls below the current command value, the switching circuit 19 shifts to the ON state. Thus, the switching circuit 19
Oscillates at a frequency determined by the inductance of the motor and the response speed of the comparator 8, and repeatedly turns on and off to keep the motor coil current constant.

As described above, it is possible to obtain a circuit configuration in which the current waveform applied to the motor coils 1a and 1b has a constant current value without being affected by the induced voltage of the motor coils 1a and 1b. Therefore, the motor coil current waveform during low-speed rotation is (7-
9), becomes constant as shown in (7-10), the rotational torque of the two-phase coil becomes as shown in (7-11), and the motor torque which is the sum of the coking torque as shown in (7-12) Therefore, the torque ripple can be held very low.

Further, since the power supply voltage is switched and applied to the motor coils 1a and 1b, there is no loss in voltage drop, the motor efficiency is remarkably improved, and the heat generation of a circuit built in the fan motor is reduced. Also, the bearing life is extended.

When the power supply voltage is turned on in the low-speed rotation command state, as shown in FIG. 7, the rotation torque (7-11) generated in the motor coil is small and the negative coking torque value (6-5) is hatched. In some cases, the motor cannot be started because the motor cannot get over the motor. For that measure,
If the power supply voltage is turned on even in the low-speed rotation command state, the rotation speed command voltage 1 corresponding to the full-speed rotation for a short time
8a through a differentiating circuit including a resistor and a capacitor,
Generates full-speed rotation torque.

When the rotational speed command value is supplied not by a DC voltage but by a PWM pulse of a certain frequency from a microcomputer or the like, the resistor / capacitor constituting the above-described differentiation circuit operates as a primary low-pass filter, and The same operation as when the command value is a DC voltage is performed.

In the motor drive control IC 4, FIG.
When the motor is mechanically constrained, the output of the amplifier 21 is fixed at a certain voltage value as shown in (8-1). At this time, in order to suppress the temperature rise of the motor coil, the energization of the motor coil is performed. It has a function of turning on and off at a certain time interval, and simultaneously outputs an alarm signal (8-2) in a restricted state. When the motor is mechanically locked in the low-speed rotation command state, the rotation torque is small as described above even if the power is turned on, and the motor may not be able to start. As a countermeasure, while the motor drive control IC 4 is generating the alarm signal, it is possible to generate a rotation torque corresponding to the full-speed rotation, and to smoothly start the motor.

[0030]

As described above, in the fan motor control circuit according to the present invention, the torque ripple during the rotation of the motor is very small, and the electromagnetic noise and vibration are small even when the rotation speed of the fan is low. . As a result, vibration of the fan blades is reduced, and low noise is possible. In addition, the variable speed method is not a power supply voltage drop method, but a method that uses the energy stored in the motor coil efficiently, so it is efficient and the circuit temperature rise inside the fan is very low. The life of the fan itself is significantly increased.

In addition, by connecting a resistor and a capacitor between the buffer circuit and the comparison circuit, the operation can be performed with a simplified circuit configuration regardless of whether the rotation speed command value is a DC voltage value or a PWM method, and the usage range is increased. Become wider.

In addition, an alarm signal output from the motor drive control IC reliably generates a starting torque at the time of restraint, at the time of starting, at the time of starting the lock recovery, and the like, so that the starting can be performed smoothly and the reliability can be improved. Can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a control circuit for a fan motor according to the present invention.

FIG. 2 is a typical circuit diagram of a conventional fan motor control circuit.

FIG. 3 is a timing chart illustrating the operation of FIG. 2;

FIG. 4 is another circuit diagram of the conventional variable speed control circuit.

FIG. 5 is another circuit diagram of a conventional fan motor control circuit.

FIG. 6 is a diagram showing characteristics of a motor generated torque.

FIG. 7 is a diagram showing characteristics of a motor-generated torque during low-speed rotation.

FIG. 8 is a diagram illustrating an operation of an alarm signal of a motor drive control IC.

FIG. 9 is an operation waveform diagram of a differentiating circuit and a first-order low-pass filter according to the present invention.

[Explanation of symbols]

1a: Motor coil 1b: Motor coil 2 ...: Conventional circuit with fixed rotation speed 3 ...: Magnetic detection element 4 ...: Motor drive control IC 5a: Transistor 5b: Transistor 6 ...: Base resistance 7 ...: Buffer circuit 8 ...: Comparator (comparison circuit) 9 ...: Current detection resistor 10 ...: Transistor 11 ...: Transistor 12 ...: Diode 13 ...: Resistor 14 ...: Capacitor 15 ...: Bias resistor 16 ...: Power switch 17 ...: Power supply voltage (Vcc) 18 ...: rotation speed command terminal 18a: rotation speed command voltage 19 ...: switching circuit 20 ...: current circulation circuit 21 ...: amplifier 22 ...: distribution circuit 23 ...: output transistor 24 ...: speed command circuit 25 ...: rotation pulse generation circuit 26, 33, 34, 35 ...: resistor 27 ...: capacitor 28 ...: transistor 29 ...: charging circuit 30: comparator 31 ...: speed switching means 32 ...: transistor 36 ...: rotation speed switching signal input terminal 41 ...: DC motor 42 ...: three-terminal regulator (3-1) ... amplifier output waveform (3-2), (3-3) Output waveform of distribution circuit (3-4) Rotation pulse generation circuit (3-5) Charge voltage waveform (3-6) Comparator output (3-7), (3-8) Current waveform flowing in two-phase coil (6-1a), (6-1b) Induced voltage waveform generated in two-phase coil during rotation (6-2a), (6-2b) Applied to motor coil during rotation (6-3a), (6-3b): Current waveform flowing in the motor coil (6-4): Rotating torque generated in the motor coil (6-5): Coking torque generated between the rotor magnet and the stator core ( 6-6) Motor Luc (7-1), (7-2): Current waveform flowing through two-phase coil during low-speed rotation (7-3): Rotational torque generated in motor coil during low-speed rotation (7-4): Low-speed rotation (7-5): Current waveform flowing in two-phase coil during low-speed rotation (7-7): Rotation torque generated in motor coil during low-speed rotation (7-8): Motor torque generated in motor coil during low-speed rotation (7-9), (7-10): Current waveform flowing through two-phase coil during high-speed rotation (7-11): Low-speed rotation (7-12) Motor torque generated in motor coil during low-speed rotation (8-1) Amplifier output (8-2) Alarm output output from motor drive control IC (9-1) ... Circuit power supply line voltage (9 2) ... differential circuit output (9-3) ... rotation command by PWM pulses (9-4) ... first-order low-pass filter output

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-205581 (JP, A) JP-A-7-274586 (JP, A) JP-A 8-182381 (JP, A) JP-A 9-204 56194 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02P 6/10 F04D 27/00 H02P 6/08

Claims (2)

(57) [Claims] A magnetic detecting element for detecting a position of a rotor having a multi-polarized permanent magnet; an energizing command signal generating circuit for generating an energizing command signal based on an output signal of the magnetic detecting element; In a control circuit for a fan motor having a plurality of transistors that are turned on and off by a command signal, a current detection resistor that detects a current flowing through a motor coil as a voltage, a voltage of the current detection resistor, a rotation speed command voltage, A switching circuit for turning on / off a power supply voltage by an output of the comparison circuit; and an energy stored in the motor coil when the switching circuit is on as a current when the switching circuit is off. A current circulating circuit that circulates through the motor coil and discharges it is provided.
Terminal, and connect a resistor to the other terminal of the above capacitor.
One terminal of the resistor is connected, and the other terminal of the above resistor is rotated
Buffer output for impedance conversion of several command voltages
And connect the connection point of the resistor and the capacitor with the above ratio.
By connecting to the input terminal of the
The capacitor operates as a differentiation circuit when the motor starts.
And a PWM pulse is input to the rotation speed command voltage.
A fan motor control circuit, which is sometimes operated as a primary low-pass filter . 2. The fan motor control circuit according to claim 1, wherein when the motor is restrained, the switching circuit is forcibly turned on by an alarm signal output from a motor drive control IC.