JP4026741B2 - Brushless motor drive circuit with overcurrent protection circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drive circuit for a brushless motor having an overcurrent protection circuit, and in particular, a brushless having an overcurrent protection circuit capable of preventing overheating damage of the drive circuit by interrupting the energization current even when the rotor is locked. The present invention relates to a motor drive circuit.
[0002]
[Prior art]
FIG. 2 shows an example of a driving circuit for a brushless motor having a conventionally known overcurrent protection circuit. 1 is a Hall element for detecting the magnetic pole position of a permanent magnet, 2 is an output of the Hall element and generates an energization control signal. Energization control signal generating circuit, 3 and 4 are energization control switching elements, 5 is a stator winding, 6 is a current detection resistor for detecting the current of the stator winding, 7 is a resistor, 8 is a capacitor, Reference numeral 10 denotes a voltage dividing resistor for generating a reference voltage for the comparison circuit, 11 is a comparison circuit, and 12 is a diode.
The energization control signal generation circuit 2 includes a logic signal generation circuit 2-1 that generates an energization signal, a pulse signal generation circuit 2-2, a voltage detection circuit 2-3 of the lock detection capacitor 33, and the same capacitor. Charging / discharging circuit 2-4 is provided.
[0003]
The operation of the drive circuit of the brushless motor having the overcurrent protection circuit according to the prior art shown in FIG. 2 will be described.
The drive circuit of the brushless motor inputs the output of the Hall element 1 to the energization control signal generation circuit 2, and two energization signals are supplied from the logic signal generation circuit 2-1 of the energization control signal generation circuit 2. The stator windings 5 are alternately energized to rotate the rotor in a predetermined direction.
[0004]
The brushless motor shown in FIG. 2 includes two stator windings, one hall element for detecting the magnetic pole of the permanent magnet, and a reluctance piece as a self-starting means (not shown), Due to the action of the reluctance piece, one of the magnetic poles of the permanent magnet is stationary at a position where it overlaps the Hall element, and when a predetermined DC voltage is applied to the power supply terminal, an output signal is output from the Hall element 1 and the energization control signal generating circuit 2 An energization signal from the logic signal generation circuit 2-1 enters, for example, the energization control switching element 3, energizes it, and energizes one of the stator windings 5, whereby the permanent magnet is attracted, rotates in a predetermined direction, and self You can start up.
[0005]
However, when a predetermined DC voltage is applied to the power supply terminal in a stationary state, no back electromotive force is generated in the stator winding 5, so the element that regulates the circuit current is the resistance of the stator winding 5. Since only the internal resistance of the energization control switching elements 3 and 4 is large, a large starting current flows.
Here, since the counter electromotive force is generated in the stator winding 5 once activated, the winding current decreases, the rotational speed increases, and the activation operation can be performed safely.
[0006]
However, in the configuration described above, when the rotor is locked, depending on the magnetic pole position, a startup hunting phenomenon occurs in which the rotor reciprocates between the forward rotation direction and the reverse rotation direction. The control switching elements 3 and 4 may overheat. Therefore, in the driving circuit according to the prior art, as shown in FIG. 2, a current detection resistor 6 is provided between the energization control switching elements 3 and 4 and the ground, and the voltage of the current detection resistor 6 is set to a time constant by the resistor 7 and the capacitor 8. The reference voltage obtained by dividing VCC by the resistors 9 and 10 is input to the + side terminal of the comparison circuit via the circuit, and the output of the comparison circuit is supplied via the diode 12 to the + side terminal of the comparison circuit. An overcurrent protection circuit configured to connect to the two outputs of the energization control signal generation circuit 2 is provided.
[0007]
In the operation of the above-described overcurrent protection circuit, when a large start-up current flows during start-up, the voltage of the current detection resistor 6 charges the capacitor 8 via the resistor 7, and the voltage is input to the negative terminal of the comparison circuit 11, When it is determined that the voltage of the capacitor 8 is higher than the reference voltage compared with the reference voltage divided by the resistors 9 and 10 and input to the + side terminal of the comparison circuit 11, the output of the comparison circuit 11 is Lo. The level of the diode 12 is turned on, the two outputs of the energization control signal generation circuit 2 are grounded, the energization control switching elements 3 and 4 are turned off, the energization of the stator winding 5 is cut off, and the overcurrent Operates as a protection circuit.
[0008]
The energization control signal generation circuit 2 includes a logic signal generation circuit 2-1, a pulse signal generation circuit 2-2 that detects rotation based on the output of the logic signal generation circuit 2-1, and a lock detection capacitor 33. The voltage detection circuit 2-4 and the same capacitor charge / discharge circuit 2-3 are provided, and the lock detection capacitor 33 is always charged by the charge / discharge circuit 2-3 and the output pulse of the pulse signal generation circuit 2-2. The voltage of the lock detection capacitor 33 is detected by the voltage detection circuit 2-4, and when it is detected that the predetermined lock detection voltage value has been reached by charging, the output of the logic signal generation circuit 2-1 And when it is detected that a predetermined automatic return voltage value has been reached by discharging, the signal is output as a signal of the logic signal generation circuit 2-1.
[0009]
When the motor is rotating normally, the charge / discharge circuit 2-3 discharges the electric charge of the lock detection capacitor 33 by the signal of the pulse signal generation circuit 2-2, so that the voltage does not rise and the voltage detection circuit When 2-4 detects that the voltage is equal to or lower than a predetermined automatic return voltage value, the logic signal generation circuit 2-1 sends an energization signal to the energization control switching elements 3 and 4, and the motor continues to rotate.
[0010]
When the rotor is mechanically locked, the output signal of the pulse signal generation circuit 2-2 is not output, so the charging / discharging circuit 2-3 stops discharging and only charges, and the voltage of the lock detecting capacitor 33 is increased. When the voltage detection circuit 2-4 detects that the voltage is equal to or higher than a predetermined lock detection voltage value, the output of the logic signal generation circuit 2-1 is cut off, and the energization control switching elements 3 and 4 are cut off. As a result, it operates as an overcurrent protection circuit and the motor stops.
When the voltage detection circuit 2-4 detects that the predetermined lock detection voltage value has been reached by charging, the lock detection capacitor 33 starts discharging by a circuit having a long time constant of the charge / discharge circuit 2-3, for a predetermined time. When the voltage detection circuit 2-4 later detects that a predetermined automatic return voltage value has been reached due to discharge, the signal of the logic signal generation circuit 2-1 is input to the energization control switching elements 3 and 4, and the rotation of the motor is automatically performed. Will return.
[0011]
[Problems to be solved by the invention]
However, when the above-described overcurrent protection circuit operates to turn off the energization control switching elements 3 and 4 and cut off the energization, the voltage of the current detection resistor 6 is lost, so the capacitor 8 is discharged and the comparison circuit 11 is reset. The output becomes the HI level, the diode 12 is turned OFF, and the two outputs of the logic signal generation circuit 2-1 provided in the energization control signal generation circuit 2 are sent to the energization control switching elements 3 and 4. The energization control switching elements 3 and 4 are turned ON, and a current flows through the stator winding 5. If an overcurrent flows again at this time, the overcurrent protection circuit operates and the energization is interrupted. This operation may be repeated, and the energization cannot be completely interrupted. There was a concern of overheating burnout of the elements 3 and 4.
[0012]
When the rotor is mechanically locked and a startup hunting phenomenon occurs, a pulse signal is generated from the pulse signal generation circuit 2-2 even though the rotor is not operating normally, and the charge / discharge circuit 2- 3 discharges the electric charge of the lock detection capacitor 33, so that the voltage of the lock detection capacitor 33 does not rise and does not lead to detection of the lock state, so that an overcurrent continues to flow. Even in such a case, there is a concern that the energization control switching elements 3 and 4 may be overheated.
[0013]
[Means for Solving the Problems]
In order to solve the above-described problems in the present invention, the overcurrent protection circuit according to the prior art, a second comparison circuit that compares the output of the current detection resistor with the second reference voltage, and the output of the second comparison circuit A second overcurrent protection circuit configured to forcibly charge a lock detection capacitor with a transistor and a diode, and to cut off an energization signal of an energization control signal generation circuit by the voltage of the lock detection capacitor By providing a circuit, it is configured so that energization can be completely interrupted.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0015]
【Example】
FIG. 1 is a circuit diagram of a drive circuit for a brushless motor having an overcurrent protection circuit according to the present invention.
In FIG. 1, it comprises a Hall element 1, an energization control signal generation circuit 2, an energization control switching elements 3 and 4, a stator winding 5, a current detection resistor 6, a resistor 7, a capacitor 8, a diode 12, and a first comparison circuit 20. The configuration and the energization control signal generation circuit 2 include a logic signal generation circuit 2-1, a pulse signal generation circuit 2-2, a voltage detection circuit 2-4 of the lock detection capacitor 33, and a charge / discharge circuit 2-3 of the same capacitor. The arrangement is the same as that of the prior art shown in FIG. A resistor 7 and a capacitor 8 are connected in series between a connection point between the current detection resistor 6 and the energization control switching elements 3 and 4 and the ground, and a connection point between the resistor 7 and the capacitor 8 is a first comparison circuit. The negative side terminal 20 of Vcc is connected to the resistor 21, the resistor 22, and the resistor 23 in series, and the connection point between the resistor 21 and the resistor 22 and the positive side terminal of the first comparison circuit 20 are connected. The output terminal of the circuit 20 is connected to the output side of the logic signal generation circuit 2-1 provided in the energization control signal generation circuit 2 via the two diodes 12 as shown in FIG. In the same way, as a new configuration, a resistor 25 and a capacitor 24 are connected in series between the negative terminal of the first comparison circuit 20 and the ground, and the connection point between the resistor 25 and the capacitor 24 is the second comparison. The negative terminal of the circuit 27, the resistor 22 and the resistor 23 is connected to the positive side terminal of the second comparison circuit 27, the output terminal of the second comparison circuit 27 is connected to VCC via the base of the first transistor 28 and the resistor 30, and the collector of the first transistor 28 is connected to the first terminal. The base of the second transistor 29 and the resistor 31 are connected to VCC, the base of the second transistor 29 is connected to the diode 32, and the lock detecting capacitor 33 is connected between the diode 32 and the ground. The connection point is the voltage detection circuit 2-4 provided in the energization control signal generation circuit 2, and the collector of the second transistor 29 is connected to the + side terminal of the second comparison circuit via a resistor, and the second transistor 29 and the second transistor 29 are connected. Each emitter of one transistor 28 is configured to be connected to ground.
[0016]
The operation of the overcurrent protection circuit according to the present invention shown in FIG. 1 will be described.
The overcurrent at the time of startup is converted into a voltage by the current detection resistor 6, and this voltage is input to the negative terminal of the first comparison circuit 20 through a time constant circuit composed of the resistor 7 and the capacitor 8. A resistor 21, a resistor 22, and a resistor 23 are connected in series between Vcc and ground, and a voltage dividing circuit is formed by the resistor 22 and the resistor 23, and the resistor 21 and the resistor 22 forming the voltage dividing circuit are connected. The voltage at the point is input as a reference voltage to the negative terminal of the first comparison circuit 20 and is compared by the first comparison circuit. If it is determined that the voltage at which the overcurrent is detected is higher than the reference voltage, the output of the first comparison circuit becomes Lo level, the diode 12 is turned on, and the output of the energization control signal generation circuit 2 becomes ground level. The energization control switching elements 3 and 4 are turned OFF, and the energization to the winding is cut off.
[0017]
Since the voltage of the current detection resistor 6 disappears when the energization is interrupted as described above, the voltage at the negative terminal of the first comparison circuit 20 becomes lower than the reference voltage. Thus, when the voltage at the negative terminal of the first comparison circuit 20 becomes lower than the reference voltage, the output of the first comparison circuit becomes HI level, the diode 12 is turned off, and the energization control switching element is generated by the output of the energization control signal generation circuit 2. 3 and 4 are turned ON and energization of the windings is resumed. That is, with the configuration of only the first overcurrent protection circuit according to the prior art, the above operation is repeated, and overheating of the energization control switching elements 3 and 4 cannot be avoided.
[0018]
In the present invention, when the first overcurrent protection circuit is operated as described above, the second overcurrent protection circuit is subsequently operated, and the voltage of the negative terminal of the first comparison circuit 20 is changed between the resistor 25 and the capacitor. 24 is input to the negative terminal of the second comparison circuit 27 through the time constant circuit 24, and is compared with the reference voltage input from the connection point of the resistor 22 and the resistor 23, and the voltage of the negative terminal of the second comparison circuit 27 Is higher than the reference voltage, the output of the second comparison circuit 27 becomes Lo level, the first transistor 28 is turned OFF, the base of the second transistor 29 becomes HI level, and the resistance 31 from VCC The lock detection capacitor 33 is charged via the diode 32.
[0019]
When the voltage detection circuit 2-4 detects that the terminal voltage of the lock detection capacitor 33 reaches a predetermined voltage by charging, the signal of the logic signal generation circuit 2-1 is cut off, and the energization control switching element 3; 4 is turned off and the power is cut off. When the energization is cut off, the voltage of the current detection resistor 6 is not output, the second comparison circuit 27 is reset, and the output becomes the HI level. Therefore, the first transistor 28 is turned on and the collector of the first transistor 28 is turned on. The lock detection capacitor 33 cannot be charged via the diode 32 due to the ground level, but the voltage of the lock detection capacitor 33 is blocked and held by the diode 32, so that the voltage detection circuit 2-4 continues. Since the output signal of the logic signal generation circuit 2-1 is detected by detecting that the voltage is equal to or higher than the automatic return voltage value, the energization control switching elements 3 and 4 are continuously turned off, and the energization is completely interrupted. Therefore, overheating can be prevented.
[0020]
When the first overcurrent protection circuit automatically recovers and is energized again, and the protection circuit operates again and repeats automatic recovery, the lock detection capacitor 33 is charged little by little, When the detection circuit 2-4 detects that the voltage of the lock detection capacitor 33 has reached a predetermined lock detection voltage value by charging, the output of the logic signal generation circuit 2-1 is cut off, and the energization control switching element 3 No energization signal is input to 4 and the energization of the winding is cut off.
[0021]
When the energization is cut off, the voltage of the lock detection capacitor 33 starts to be discharged by a circuit having a long time constant of the charge / discharge circuit 2-3, and after a predetermined time, the voltage detection circuit 2-4 performs a predetermined automatic by discharge. When it is detected that the return voltage value has been reached, a signal of the logic signal generation circuit 2-1 is output, an energization signal is sent to the energization signal switching elements 3 and 4, and the rotation of the motor is resumed.
[0022]
As described above, in the combination of the lock detection circuit based on rotation detection and the first overcurrent protection circuit according to the conventional technique, the lock detection is not perfect. However, the second overcurrent protection circuit is added, Is detected and the lock detection capacitor 33 is forcibly charged, the energization current can be reliably cut off, and the energization control switching element can be prevented from being burned out.
In addition, after the elapse of a predetermined time since the energization is cut off, it is possible to detect that the voltage of the lock detection capacitor has reached a predetermined automatic return voltage value, and to automatically resume energization and operate the motor. .
[0023]
The drive circuit of the brushless motor having the overcurrent protection circuit according to the present invention shown in FIGS. 1 and 2 is configured by connecting normal circuit components, but the energization control circuit, the first overcurrent protection circuit, the second The overcurrent protection circuit can also be configured as an integrated circuit.
[0024]
【The invention's effect】
Since the brushless motor drive circuit having the overcurrent protection circuit according to the present invention has the above-described configuration, the second overcurrent is maintained even in a state where the rotor is locked and the overcurrent continues to flow. The protection circuit is activated to cut off the energized current, and after a predetermined time after the energization is cut off, the energization can be completely stopped until the energization is restored by the operation of the automatic return circuit, thus preventing the energization control switching element from being burned out. In addition, there is an effect that automatic recovery is possible.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a drive circuit of a brushless motor having an overcurrent protection circuit according to the present invention.
FIG. 2 is a circuit diagram of a driving circuit for a brushless motor having an overcurrent protection circuit according to the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 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 3, 4 Energization control switching element 5 Stator winding 6 Current detection Resistor 7 Resistor 8 Capacitor 9, 10 Voltage dividing resistor 11 Comparison circuit 12 Diode 20 First comparison circuit 21 Resistance 22, 23 Voltage dividing resistor 24 Capacitor 25 Resistance 27 Second comparison circuit 28 First transistor 29 Second transistor 30, 31 Resistance 32 Diode 33 Lock detection capacitor

Claims (2)

A stator having a stator winding wound thereon, a rotor having a permanent magnet rotatably supported by the stator facing a gap, and a Hall element for detecting a magnetic pole position of the permanent magnet And an energization control circuit including an energization control signal generation circuit controlled by the output of the Hall element, an energization control switching element, and a current detection resistor. The energization control circuit energizes the stator winding. A drive circuit for a brushless motor that rotates the rotor in a predetermined direction. The energization control signal generation circuit includes a logic signal generation circuit, a pulse signal generation circuit, a voltage detection circuit for a lock detection capacitor, and charging of the capacitor. A first comparison circuit that has a discharge circuit and compares the output of the current detection resistor with a first reference voltage; an output of the first comparison circuit; and an output of the logic signal generation circuit. And a first overcurrent protection circuit configured to control the output of the logic signal generation circuit with the two diodes connected between the diodes, and an output of the current detection resistor; A second comparison circuit for comparing with a second reference voltage, a transistor controlled by the output of the second comparison circuit, and a diode are provided, and the charging current of the lock detection capacitor is controlled by the transistor and the diode. A drive circuit for a brushless motor having an overcurrent protection circuit, further comprising a second overcurrent protection circuit configured to do so. 2. The brushless having an overcurrent protection circuit according to claim 1, wherein the energization control signal generation circuit, the first overcurrent protection circuit, and the second overcurrent protection circuit are configured as an integrated circuit. Motor drive circuit.

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