JP2003164184A - Drive circuit for brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a drive circuit for a brushless DC motor which prevents overheating/burnout of an energizing control transistor and a stator winding, by decreasing an energizing current when heavily loaded or locked. <P>SOLUTION: The drive circuit for a brushless DC motor is provided with a comparison circuit to compare an output voltage of a revolution speed detection circuit with a reference voltage corresponding to a revolution speed when heavily loaded, and is constituted so as to decrease the base current of the energizing control transistor, by detecting that the output voltage of the revolution speed detection circuit is lower than the reference voltage by the comparison circuit, and to decrease the energizing current. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a brushless DC motor, and more particularly to a drive circuit provided with a protection circuit against a heavy load or a lock. 2. Description of the Related Art FIG. 2 shows a small brushless D according to the prior art.
A main part circuit diagram of an example of a drive circuit of the C motor is shown. As shown in the figure, a Hall element 1 for detecting a magnetic pole position of a permanent magnet provided in a rotor and an output of the Hall element 1 are processed. An energization control signal generation circuit 2 for outputting an energization signal, energization control transistors 3 and 4 driven by the energization signal of the energization control signal generation circuit 2,
A logic signal generating circuit 2-1 for processing the output of the Hall element 1 and generating an energizing control signal. A pulse signal generating circuit 2-2 for obtaining an output of the logic signal generating circuit 2-1 to generate a pulse signal proportional to the rotation speed of the rotor; a lock detecting capacitor 2-5; A discharge circuit 2-3 and a voltage detection circuit 2-4 for detecting the voltage of the capacitor are provided. FIG. 2 shows a prior art brushless DC.
The operation of the motor drive circuit is as follows. The Hall element 1 detects the position of the magnetic pole of the permanent magnet constituting the rotor, and the energization control signal generation circuit 2 processes the output of the Hall element 1 in the logic signal generation circuit 2-1. To generate two energization signals,
The current is sent to the energization control transistors 3 and 4, and the energization control transistors 3 and 4 are alternately turned on to alternately energize the two stator windings 5 to rotate the rotor in a predetermined direction. However, when the rotor is mechanically locked in the rotating operation state, the conduction control transistors 3, 4
Large current flows, and the conduction control transistors 3, 4 and the stator winding 5 may be overheated and burnt out. In preparation for such a case, the energization control signal generation circuit 2 includes a pulse signal generation circuit 2-2 for detecting rotation based on the output of the logic signal generation circuit 2-1 and a lock detection capacitor 2-5.
And a charging / discharging circuit 2- of the lock detecting capacitor 2-5.
3 and a voltage detection circuit 2-4 for the lock detection capacitor 2-5.
Is constantly charged by the charge / discharge circuit 2-3 and discharged by the signal of the pulse signal generation circuit 2-2, and the voltage of the lock detection capacitor 2-5 is detected by the voltage detection circuit 2-4. When it is detected that the voltage has reached the predetermined lock detection voltage value by charging, the signal of the logic signal generation circuit 2-1 is cut off, and when it is detected that the voltage has reached the predetermined automatic return voltage value by discharging, a logic signal is generated. The circuit 2-1 is configured to output a signal. When the brushless DC motor is rotating normally, the charge / discharge circuit 2-3 discharges the lock detecting capacitor 2-5 by the signal of the pulse signal generating circuit 2-2, so that the voltage rises. No, voltage detection circuit 2-4
Is less than a predetermined automatic return voltage value,
The logic signal generation circuit 2-1 sends an energization signal to the energization control transistors 3 and 4, and the motor continues to rotate. On the other hand, when the rotor is locked, no signal is output from the pulse signal generation circuit 2-2.
-3 stops discharging and charges only, the voltage of the lock detection capacitor 2-5 rises, and the voltage detection circuit 2-4
, The output of the logic signal generation circuit 2-1 is cut off, the energization control transistors 3 and 4 are shut off, the motor stops, and is fixed to the energization control transistors 3 and 4. The overheating of the child winding 5 is prevented. Then, when the voltage detection circuit 2-4 detects that a predetermined lock detection voltage value has been reached by charging, the lock detection capacitor 2-5 discharges by the discharge circuit having a long time constant of the charge / discharge circuit 2-3. When the voltage detection circuit 2-4 detects that the discharge has reached a predetermined automatic return voltage value after a predetermined time, the logic signal generation circuit 2
The signal of -1 is input to the energization control transistors 3 and 4,
The rotation of the motor is automatically restored. The circuit provided in the energization control signal generating circuit 2 for detecting the lock and automatically returning the lock is detected while the power is supplied while the locked state is maintained. The operation current must be within a range where the temperatures of the conduction control transistor and the stator winding do not exceed the limit value. However, demands for smaller and higher performance brushless DC motors are increasing, and higher output is required for existing sizes. As a countermeasure, by increasing the input by lowering the impedance of the winding to increase the output, the current at the time of lock increases, and the lock detection circuit according to the prior art uses the lock detection circuit at the time of high load or lock. There has been a problem that the temperature rise is high and the winding cannot be protected. In an energizing circuit between the energizing control transistor and the stator winding in the locked state of the drive circuit of the brushless DC motor, assuming that the supply voltage is V, the winding resistance is Ra, the current is Ia, and the transistor CE is If the saturation voltage between them is Vce (sat), V = RaIa + Vce (sat), and the saturation voltage Vce (sat) between C and E when the transistor is driven to the saturation current is usually less than 1V. Therefore, in the locked state, the supply voltage is almost applied to the windings, and the windings bear the entire loss.In a high-output brushless DC motor with a low winding impedance, the winding temperature exceeds the limit value and overheating burns out. There was a danger to do. The present invention reduces the temperature at the time of locking, reduces the temperature rise of the stator winding by sharing the loss between the stator winding and the conduction control transistor, and has a high output without fear of overheating and burning. An object of the present invention is to provide a brushless DC motor drive circuit that can cope with the above. A drive circuit for a brushless DC motor according to the present invention compares a voltage whose speed is detected by a rotation speed detection circuit with a reference voltage corresponding to a rotation speed under a high load. A comparison circuit is provided, which detects that the voltage of the rotation speed detection circuit is equal to or lower than the reference voltage, reduces the base current of the conduction control transistor, increases the voltage drop Vce of the conduction control transistor, and limits the current. ,
The configuration is such that the stator winding and the conduction control transistor share the burden of loss during high load and locking. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a main part of an example of a brushless DC motor driving circuit according to the present invention. In FIG. 2, the output of an energization control signal generating circuit 2 is added to the circuit of the prior art shown in FIG. The energization control signal generation circuit 2 includes an output of the logic signal generation circuit 2-1 and an output of the rotation speed detection circuit 10. The output of the FV conversion circuit 11 is input to one of the comparison circuits 12 and the output of the reference voltage generation circuit 13 is input to the other of the comparison circuits 12, and the output of the comparison circuit 12 is It is configured to be input to the other of the base current control circuit 14 and to connect the output terminal of the base current control circuit 14 to the bases of the conduction control transistors 3 and 4. The operation of the drive circuit of the brushless DC motor according to the present invention shown in FIG. 1 is as follows. The signal of the Hall element 1 is processed by the logic signal generation circuit 2-1 of the conduction control signal generation circuit 2 and the base current control circuit 14 , And outputs the output of the base current control circuit 14 to the conduction control transistors 3 and 4.
Is applied to the stator winding 5 to rotate the rotor by rotating the pulse signal obtained from the logic signal generation circuit 2-1 of the conduction control signal generation circuit 2 in the same manner as in the above-described prior art. The number detection circuit 10 converts the voltage into an AC voltage proportional to the number of revolutions, and inputs the F-V conversion circuit 11 to convert the voltage into a voltage proportional to the frequency of the AC voltage. Output voltage of conversion circuit 11 and reference voltage generation circuit 13
The output voltage of the FV conversion circuit 11 is higher than the output voltage of the reference voltage generation circuit 13. If the output voltage of the FV conversion circuit 11 is higher than the output voltage of the reference voltage generation circuit 13, the base current control circuit 14 When a large current flows to the base and a saturation current flows between C and E of the conduction control transistor, and the output voltage of the FV conversion circuit 11 is lower than the output voltage of the reference voltage generation circuit 13, The base current control circuit 14 controls a small current to flow through the bases of the conduction control transistors 3 and 4 so that an unsaturated current flows between C and E of the conduction control transistors. When the brushless DC motor is rotating normally, the output voltage of the rotation speed detection circuit 10 is a normal value, the output voltage of the FV conversion circuit 11 is also a normal value, and the FV conversion The normal value voltage is input from the circuit 11 to one of the comparison circuits 12 and the output voltage of the reference voltage generation circuit 13 corresponding to the rotation speed under a high load is input to the other one. When detecting that the voltage of the -V conversion circuit 11 is higher than the output voltage of the reference voltage generation circuit 13, the output signal of the comparison circuit 12 controls the base current control circuit 14 so that the conduction control transistors 3 and 4 To allow a saturation current to flow between C and E. In such control, the energization control transistors 3 and 4 perform switching control, and the voltage drop Vce between C and E is reduced, and a normal operation state with high efficiency is achieved. When the load of the brushless DC motor increases and the rotation speed decreases, and the output voltage of the FV conversion circuit 11 becomes lower than the voltage of the reference voltage generation circuit 13, the output signal of the comparison circuit 12 The current control circuit 14 is controlled to supply a small base current to the conduction control transistors 3 and 4 so that an unsaturated current flows between CE. In such a control, the energization control transistors 3 and 4 are CE-
Since the unsaturated current flows between them, the CE-to-CE voltage drop Vce increases, and the average current decreases, the conduction control transistor 3,
4 and the current flowing through the stator windings decrease, the temperature decreases and the motor continues to rotate while avoiding overheating and burning. When the rotor is locked, the output voltage of the FV conversion circuit 11 becomes zero.
Controls the base current control circuit 14 to cause an unsaturated current to flow between C and E to the bases of the conduction control transistors 3 and 4, and to generate a pulse signal provided in the conduction control signal generation circuit 2. When the output of the circuit 2-2 stops and the lock detection capacitor 2-5 is charged and its voltage rises, and the voltage detection circuit 2-4 detects that the voltage has reached a predetermined lock detection voltage or more, a logic Signal generation circuit 2
Since the signal of -1 is cut off and the conduction control transistors 3 and 4 are cut off and no current flows through the stator windings, the temperature rise of the stator windings and the conduction control transistors 3 and 4 is suppressed. When the voltage detection circuit 2-4 detects that the lock detection voltage has reached a predetermined lock detection voltage value, the charge / discharge circuit 2-3 starts discharging via a discharge circuit having a long time constant, and a predetermined time. When the voltage detection circuit 2-4 later detects that the voltage has reached the predetermined automatic return voltage value, the signal of the logic signal generation circuit 2-1 is input to the base current control circuit 14, and the base current control circuit 14 As described above, since the signal is input so that the base current flows through the unsaturated current between C and E, the current flowing by the operation of the automatic return circuit is maintained at a lower value than in the normal state. 3, 4 and the temperature rise of the stator winding can be suppressed. As described above, at the time of high load or lock, the base current of the conduction control transistors 3 and 4 is reduced to achieve CE.
By reducing the conduction current by using the current between them as the unsaturated current, the loss inside the conduction control transistors 3 and 4 increases, but the current in the stator winding 5 decreases and the current in the stator winding decreases. , The total loss is shared between the stator winding and the conduction control transistors 3 and 4,
Temperature rises of the stator winding and the conduction control transistors 3 and 4 are suppressed, and overheating and burning can be prevented. Since the rotation speed of the rotor is zero at the time of starting, the output of the rotation speed comparison circuit 12 controls the output of the base current control circuit 14 so that an unsaturated current flows through the conduction control transistors 3 and 4. However, the FV conversion circuit 1 in which the rotation speed has increased after startup and the output of the rotation speed detection circuit 10 has been obtained.
1 is compared with the output of the reference voltage generation circuit by the comparison circuit 12, and when it is detected that the output of the FV conversion circuit 11 exceeds the output of the reference voltage generation circuit 13, the base current control circuit 14 Output a large base current to the conduction control transistors 3 and 4, and control so that a saturation current flows between C and E of the transistors to maintain normal rotation. The drive circuit of the brushless DC motor according to the present invention has the above-described configuration, so that when the load becomes high, the current of the conduction control transistor is reduced to continue the conduction. When the lock state is attained, energization is cut off and the current at the time of automatic recovery is reduced, so that overheating and burning of the energization control transistor and the stator winding can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a main part circuit diagram of an example of a drive circuit of a brushless DC motor according to the present invention. FIG. 2 is a main part circuit diagram of an example of a conventional brushless DC motor drive circuit. [Description of Signs] 1 Hall element 2 Energization control signal generation circuit 2-1 Logic signal generation circuit 2-2 Pulse signal generation circuit 2-3 Charge / discharge circuit 2-4 Voltage detection circuit 2-5 Lock detection capacitors 3 and 4 Energization control transistor 5 Stator winding 10 Revolution detection circuit 11 FV conversion circuit 12 Comparison circuit 13 Reference voltage generation circuit 14 Base current control circuit

Claims (1)

Claims: 1. A stator having a stator winding wound thereon, a rotor having a permanent magnet and a fan, which are rotatably supported opposite to the stator, and With the Hall element for detecting the magnetic pole position, an energization control signal generation circuit controlled by the output of the Hall element, and an energization control circuit including an energization control transistor, the stator control winding is provided by the energization control circuit. A brushless DC motor drive circuit frequently used in a small axial flow fan or the like that energizes and rotates the rotor in a predetermined direction, wherein the energization control signal generation circuit includes a logic signal generation circuit, a pulse signal generation circuit, and a lock. In a device having a detection capacitor, a voltage detection circuit for a lock detection capacitor, and a charge / discharge circuit for the capacitor, the speed is detected from the output of the logic signal generation circuit. A rotation speed detection circuit, a comparison circuit for comparing an output voltage of the rotation speed detection circuit with a reference voltage, and a base current control circuit controlled by an output of the comparison circuit. And a control circuit for controlling the current of the conduction control transistor.