JPH0621396U - Brushless motor drive circuit - Google Patents

Abstract

(57) [Summary] [Purpose] Without using external parts such as capacitors,
Provided is a brushless motor that can suppress switching pulses. [Configuration] The output signal of the position signal amplification circuit 2 stabilized by the AGC circuit 3 is used, and the switching circuit 5 configured in parallel prevents the output circuits 7 from being energized simultaneously during phase switching. Further, the output current is monitored by the resistance of the pre-drive circuit 6, the voltage is divided by the resistance of the NF circuit 8, and negative feedback is applied by the NF circuit 8 only during phase switching. Therefore, the time change of the output current is alleviated,
The switching pulse can be effectively suppressed.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a drive circuit for a brushless motor, and more particularly to reduction of switching pulses when switching phases.

[0002]

[Prior art]

 In recent years, small DC motors have been recognized for their good controllability not only in the acoustic field but also in the information and industrial fields, and their applications are expanding with great momentum. Among them, brushless motors have no contact parts such as brushes and commutators, and have the advantage of long life. Therefore, their applications are expanding as industrial motors where reliability is particularly important.

Under such circumstances, the driving method of the small axial fan has been switched from AC to DC in recent years, and the number of DC axial fans using brushless motors has been increasing.

The DC axial fan is required to house the drive circuit in a limited space and to be low in cost. In order to realize these things, a two-phase half-wave method that can be driven by one magnetic detection element and has simple wiring is adopted. In addition, in order to simplify the circuit and increase efficiency, the output circuit generally performs a switching operation and suppresses the generated switching pulse with a capacitor or a Zener diode.

FIG. 4 shows a conventional brushless motor drive circuit, which is a method in which a capacitor is inserted, and FIG. 6 shows output waveforms of FIG. 4 and FIG. 5 described later. As shown in FIG. 4, the collector of the transistor 82 whose base is connected to the output terminal of the Hall IC 81 has one end of the resistor 83 whose other end is connected to VCC and the diode 84 of the diodes 84, 85 connected in series. Is connected to the anode, the emitter is connected to one end of a resistor 86 whose other end is connected to GND, and the base of an output transistor 87 whose emitter is connected to GND.

The collector of the output transistor 87 is connected to one end of a capacitor 88 whose other end is connected to GND and is also connected to VCC via a drive coil 89 of the motor. The base of the output transistor 91 whose emitter is connected to GND is connected to one end of a resistor 90 whose other end is connected to GND and is connected to the cathode side of the diode 85, and the other end of which is connected to GND. The capacitor 92 is connected to one end of the capacitor 92, and is also connected to VCC through the drive coil 93 of the motor. The output circuit 94 is formed within the frame surrounded by the broken line.

In the drive circuit of FIG. 4, the output current waveform shown in FIG. 6 (a) is a switching pulse (virtual induced voltage B) as shown in FIG. 6 (b) which is generated at the time of phase switching if no measures are taken. The output voltage waveform has. The switching pulse generated at the time of phase switching can be reduced by obtaining the switching pulse (virtual induced voltage C) as shown in FIG. 6 (c) by optimally selecting the capacitances of the capacitors 88 and 92. , I do not get a satisfactory result.

That is, if the capacitances of the capacitors 88 and 92 are small, there is no effect. If the capacitances are increased, a time delay occurs as shown in FIG. 6 (c), which hinders the switching timing or drives the motor. The resonance energy with the coil increases and it may flow back to the power supply. Therefore, the current situation is that a compromise of about several μF is made.

[0009]

[Problems to be solved by the device]

 As described above, in the axial fan motor, circuit components must be mounted in a limited space, so it is necessary to reduce external components and promote IC integration. In such a case, there is a method of using a Zener diode instead of the capacitor as a method of not using the two capacitors 88 and 92 of several μF as shown in FIG. FIG. 5 shows another brushless motor drive circuit, which is an output circuit obtained by changing one phase of the output circuit 94 in FIG. That is, the collector of the output transistor 104, whose emitter is connected to GND, is connected to VCC via the motor drive coil 105 and to the cathode side of the Zener diode group 103, and the base is connected to GND via the resistor 101. They are connected and connected to the anode side of the Zener diode group 103 via the resistor 102. Although such a drive circuit can be integrated into an IC without problems, the switching noise (virtual induced voltage D) generated during phase switching becomes rather large as shown in FIG. 6 (d). was there.

It is an object of the present invention to provide a drive circuit for a brushless motor which is suitable for use as an IC, while suppressing the switching pulse without using external parts to prevent the generation of switching noise.

[0011]

[Means for Solving the Problems]

 The present invention is directed to a position signal amplification circuit for correcting variations in the output sensitivity of a magnetic detection element for detecting the rotational position of a rotor by an automatic amplification degree control circuit (hereinafter referred to as AGC circuit), and an output of the position signal amplification circuit. A switching circuit that distributes a signal to each phase via a buffer circuit, a predrive circuit that includes a resistor that is provided to monitor the output current that is distributed by the switching circuit, and a resistance of the predrive circuit. A negative feedback (NF) circuit that divides the voltage generated at the end by resistance division and negatively feeds back to the output end of the buffer circuit is provided, and negative feedback is applied while the predrive circuit is switched from on to off. It was done.

[0012]

[Action]

 According to the present invention, by having an NF circuit, it is possible to prevent the generation of switching pulses without using external parts, and the circuit configuration is optimal for IC implementation, so it can be mounted in a limited space. A compact IC can be obtained.

Further, since the external parts are eliminated, the material cost of the drive circuit and the man-hours can be reduced, and an inexpensive motor can be obtained.

[0014]

【Example】

 FIG. 1 shows a driving circuit according to an embodiment of the present invention. Reference numeral 1 is a magnetic detection circuit composed of a magnetic detection element 11 and a resistor 12. The output terminal of the magnetic detection element 11 is a position signal described later. They are connected to the bases of the transistors 19 and 20 which form the differential amplifier in the amplifier circuit 2, respectively.

Reference numeral 2 is a position signal amplifier circuit composed of the transistors 19 and 20 and resistors 17, 18, 21 and 22. The collectors of the transistors 19 and 20 are located on the anode side of the detection diodes 15 and 16. They are each connected and connected to V CC through resistors 17 and 18, respectively.

Reference numeral 3 denotes transistors 26 and 27 forming a differential amplifier, transistors 24 and 25 forming a current mirror, a control transistor 14, the detection diodes 15 and 16 and an external capacitor 13. The configured AGC circuit compares the reference voltage FE applied to the base of the transistor 27 with the detection output D E of the detection diodes 15 and 16 to stabilize the output of the position signal amplification circuit 2.

Reference numeral 4 denotes a buffer circuit composed of transistors 29 and 30, the bases of which are connected to the collectors of the transistors 20 and 19, respectively.

Reference numeral 5 is composed of transistors 37, 38, 45 and 46, transistors 33 and 34, 35 and 36, 41 and 42, 43 and 44, and resistors 39, 40, 47 and 48, which form a current mirror circuit. In the switching circuit described above, the common bases of the transistors 37, 38 and 45, 46 are respectively connected to the emitters of the transistors 29 and 30 of the buffer circuit 4, and the collector of the transistor 37 is connected to the collectors of the transistors 33 and 41. The collector of the transistor 38 is connected to the collector of the transistor 35, the collector of the transistor 45 is connected to the collector of the transistor 42, and the collector of the transistor 46 is connected to the collectors of the transistors 36 and 43. There is.

Reference numeral 6 is a pre-drive circuit composed of transistors 50, 51, 54 and 55 and resistors 52 and 53 which form a current mirror circuit, and the collector of the transistors 50 and 54 is the collector of the transistors 44 and 34. The collectors of the transistors 51 and 55 are connected to VCC through the resistors 52 and 53 for monitoring the output current.

Reference numeral 7 is an output circuit for driving the drive coils 66 and 67 of the motor, which is composed of transistors 56 and 57, 58 and 59 which form a current mirror circuit, and the collectors of the transistors 56 and 58 are The transistors 50 and 51 are connected to the common emitters of 51 and 54 and 55, respectively, and the collectors of the transistors 57 and 59 are connected to VCC via drive coils 66 and 67 of the motor, respectively.

Reference numeral 8 divides the voltage generated across the resistors 53 and 52 of the predrive circuit 6 by the resistors 62, 63 and 64 and 65, and negatively feeds it back to the emitters (output ends) of the transistors 29 and 30 of the buffer circuit 4. It is a negative feedback (NF) circuit.

Further, 23, 28, 31, 32 and 49 are constant current sources. Although the dot-dash line 9 represents an integrated circuit, the magnetic detection circuit 1 may be incorporated in the integrated circuit 9.

FIG. 2 is a block diagram showing each circuit unit shown in FIGS. 1 to 8. In FIG. 2, 71 is a constant current circuit composed of the constant current sources 23, 28, 31, 32 and 49 shown in FIG. 1, and 72 is a general term for the drive coils 66 and 67 of the motor shown in FIG. is there.

The operation of the present invention configured as above will be described.

In the case of the two-phase half-wave drive, the induced voltage is not generated when the phases are switched, so that the current becomes large and a switching pulse determined by the rate of change of the current with time is generated. Therefore, in order to suppress this switching pulse, the magnitude of the current and the slope of the current change must be considered. Sine wave drive may be used to suppress the slope of the current change during phase switching, but if a differential amplifier with a simple configuration is used as the switching circuit, the signal levels will be the same during phase switching and Each half of the supplied current I flows to the output circuit, and both phases are turned on. In order to improve this, the applicant provided a cancel circuit as described in Japanese Patent Laid-Open No. 3-7136 and distributed the current, and always applied a current of I / 2 to the collector of the transistor so that no current was supplied to the output at the time of switching. I tried not to flow.

However, in this method, it is difficult to balance the circuit to I / 2 because the current conditions of the cancel circuit and the switching circuit are different.

In the present invention, the differential amplifier of the switching circuit 5 is a parallel type. That is, the bases of the transistors 37 and 38 and the transistors 45 and 46 are connected in common, respectively, and the collectors of the transistors 37 and 46 are connected to the output circuit 7 through the transistors 33, 34, 43 and 44 forming the current mirror. ing. Further, the collectors of the transistors 38 and 45 are connected to the collectors of the transistors 46 and 37 via the transistors 35, 36 and 41, 42 forming a current mirror, and serve to cancel the current flowing to the output. Therefore, the current flowing out from the switching circuit 5 is 0 to I / 2 for each phase. This circuit configuration is symmetrical, so it is easy to balance the circuit.

Next, since the output transistors 57 and 59 of the output circuit 7 do not operate in the saturated state as they are, heat generation becomes large, and therefore the gain needs to be increased in order to saturate them. When the gain is increased, the time change of the current becomes sharp and the switching pulse is likely to occur. Therefore, the output current (Fig. 3 (a)) is monitored by the resistors 52 and 53, and the values of the resistors 62 and 63 and 64 and 65 are set so as to divide the voltage generated across the output current to a predetermined value. . This value is negatively fed back to the emitters of the transistors 29 and 30 of the buffer circuit 4 via the resistors 61 and 60. In this way, while one of the phases of the output circuit 7 is switched from ON to OFF, negative feedback is applied and the gain is compressed. Therefore, the switching pulse suppresses the virtual induced voltage (B) as shown in FIG. 3 (b). The amount of this negative feedback is arbitrarily determined by appropriately selecting the values of the resistors 62 and 63 and 64 and 65.

Further, although not shown in the present invention, when the rotor is locked, the current of the motor drive coil is shut off and a restart pulse is periodically generated, and this lock detection circuit. It is equipped with a lock protection circuit that interrupts the current flowing in the motor drive coil in response to an output signal from the motor drive coil to prevent burnout due to overcurrent of the motor drive coil when the rotor is locked and to suppress switching pulses due to restart pulses. May be.

Of course, the one-phase full-wave drive method can also be applied.

[0031]

[Effect of device]

 As described above, the drive circuit of the brushless motor of the present invention has the NF circuit, so that switching pulses are prevented during normal rotation and when the rotor is locked without using a large external component. It is possible to provide a highly efficient drive circuit with no switching noise and a small reactive current at the time of phase switching, which is ideal for IC implementation. Therefore, the effects such as reduction of the number of parts and securing of extra space are great.

[Brief description of drawings]

FIG. 1 is a drive circuit diagram of a brushless motor according to an embodiment of the present invention.

FIG. 2 is a block diagram of FIG.

FIG. 3 is a diagram showing an output voltage waveform of FIG.

FIG. 4 is a drive circuit diagram of a brushless motor in a conventional example.

FIG. 5 is an output circuit diagram in another conventional brushless motor drive circuit.

6 is a diagram showing an output voltage waveform when the capacitor of FIG. 4 is used as a countermeasure and an output voltage waveform when the Zener diode of FIG. 5 is used as a countermeasure.

[Explanation of symbols]

1 ... Magnetic detection circuit, 2 ... Position signal amplification circuit, 3 ... A
GC circuit, 4 ... Buffer circuit, 5 ... Switching circuit, 6
... Pre-drive circuit, 7 ... Output circuit, 8 ... NF circuit, 71 ... Constant current circuit, 72 ... Coil.

Claims (2)

[Scope of utility model registration request] 1. A position signal amplifier circuit configured to correct an output sensitivity variation of a magnetic detection element for detecting a rotational position of a rotor by an automatic amplification degree control circuit, and a buffer circuit for an output signal of the position signal amplifier circuit. A switching circuit for distributing to each phase via a pre-drive circuit including a resistor provided for monitoring the output current distributed by the switching circuit, and a voltage generated across both ends of the resistance of the pre-drive circuit is resistance-divided. And a negative feedback circuit for performing negative feedback to the output end of the buffer circuit, until the predrive circuit is switched from on to off,
A drive circuit for a brushless motor, characterized in that negative feedback is applied. 2. A lock detection circuit that cuts off the current of the motor drive coil when the rotor is locked and periodically generates a restart pulse, and receives an output signal from the lock detection circuit and flows to the motor drive coil. 2. A brushless according to claim 1, further comprising: a lock protection circuit for connecting and disconnecting a current to prevent burnout due to an overcurrent of the motor drive coil when the rotor is locked and to suppress a switching pulse due to a restart pulse. Motor drive circuit.