JPS631599Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a forward/reverse drive circuit for a motor using bidirectional transistors.

Conventionally, in motor drive circuits that turn on and off NPN or PNP transistors to flow drive current to the coil, the transistor and A diode is inserted in parallel to prevent overvoltage. However, in motor drive circuits that can drive the coil in both directions using a bidirectional transistor with symmetrical electrical characteristics between the collector and the emitter, such as a motor drive circuit that can be reversed and reversed, the overvoltage blocking diode is connected to the emitter of the transistor. When inserted between the collectors, such an overvoltage blocking diode cannot be used because it forms a short circuit for a power source of reverse polarity, for example.

The present invention provides a forward/reverse drive circuit for a motor that solves this problem. a bidirectional transistor with a collector emitter connected between the first and second excitation coils, which divide the coil into two; and an overvoltage prevention transistor connected in series with opposite polarities and in parallel between the collector emitters of the transistors. and a forward/reverse switch that switches the polarity of the power line to change the direction of rotation of the motor, and the Zener voltage of the Zener diode is determined from the collector emitter breakdown voltage of the bidirectional transistor. It is characterized by having a value that is low and higher than the voltage between the power supply lines.

According to this configuration, the overvoltage that occurs in both directions due to the reverse breakdown voltage (Zener breakdown voltage) of the pair of Zener diodes is limited, and the bidirectional transistor is protected no matter which polarity of power is supplied. Furthermore, the breakdown voltage of a pair of oppositely connected Zener diodes prevents the formation of a short circuit with respect to power supplies of both polarities, making it possible to switch the power supply polarity and reverse the polarity.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a drive circuit diagram of a two-phase switching type brushless motor to which the present invention is applied, and FIG. 2 shows a back electromotive voltage waveform applied to a switching transistor. This brushless motor includes two-phase coils L _A -L _A ′ and L _B -L _B ′. The coils of each phase (L _A and L _A ′ or L _B and L _B ′) are in the same phase position in electrical angle (for example, a phase difference of 360° in electrical angle).
The bidirectional transistors T3 and T4 are connected in series through their collector-emitters.

Although this brushless motor is not shown, the winding pitch of each coil (the opening angle between the outward and return paths) is adjusted so that a rotational dead center with zero torque does not occur at electrical angles of 0° and 180° (the reversal position of the field pole). ) is selected to be 180° or less in electrical angle (for example, 120°), and a distortion means is provided to distort the magnetic flux pattern acting on the coil in the vicinity of 180° in electrical angle of the field pole.

In FIG. 1, the rotational position of the rotor is detected by a Hall element 1, and its output is supplied to the inputs of differential amplifiers 2 and 3 with opposite polarities. Therefore, sinusoidal amplified outputs with opposite polarities are obtained from the outputs of the differential amplifiers 2 and 3, and these outputs are transmitted to the pair of transistors T constituting the differential switch circuit 4.
1, supplied to the base of T2. As a result, the on/off states of the transistors T1 and T2 are reversed at the level cross point of the outputs of the differential amplifiers 2 and 3, and a switching signal is obtained from the collectors of the transistors, which alternately go high at 180 degrees in electrical angle. This switching signal is supplied to the bases of bidirectional transistors T3 and T4, and the coils L _A -L _A ' and L _B -L _B ' are energized according to whether T3 or T4 are turned on or off.

The drive voltage V2 (servo voltage) supplied to each coil is applied to the coil L _A , through the forward/reverse switch 5.
Since it is selectively supplied to one end of L _B (line S1) or one end of coils L _A ′ and L _B ′ (line S2),
Depending on the operation of the switch 5, current flows through the coil in either direction, causing the motor to rotate forward or reverse. Common emitter resistance R2 of differential switch circuit 4
is the driving voltage V2 from the selected power supply line S1, S2 via the diodes D1, D2.
is supplied. The collector currents of the transistors T1, T2 flow from the bases of the transistors T3, T4 through the collectors or emitters in the direction of one of the selected ground lines S1, S2.

Zener diodes ZD1 and ZD2 connected in series with opposite polarities are connected between the collector emitters of the bidirectional transistors T3 and T4, respectively. When the transistor T3 (or T4) is turned off, a pulsed back electromotive voltage as shown in FIG. 2a is induced in the collector or emitter of T3 depending on the current direction of the coil L _A -L _A '.

Assuming that the forward voltage of Zener diodes ZD1, ZD2 is V _F and the Zener voltage is V _Z , if this back electromotive voltage exceeds V _F +V _Z , the diodes ZD1, ZD
2 is turned on and the other undergoes Zener breakdown, and the back electromotive voltage applied to the transistor T3 is limited to V _F +V _Z as shown in FIG. 2B.

Therefore, when V _CEO is the maximum rating of the collector emitter of transistor T3 or T4, if V _Z is selected so that V _F +V _Z ≦V _CEO , there is no risk of the bidirectional transistor being destroyed.

Further, if V _Z >V2, the power supply will not be short-circuited by the diodes ZD1 and ZD2 in either forward or reverse rotation.

As shown in FIG. 3, a series circuit in which the cathodes of Zener diodes ZD1 and ZD2 are connected may be inserted between the collector and emitter of the bidirectional transistor.

As mentioned above, the present invention uses bidirectional transistors to switch the rotation direction of the motor, and arranges the excitation coil symmetrically with respect to the bidirectional transistor so that reversal switching can be performed simply by reversing the polarity of the power supply. When switching the polarity of the power supply, a series reverse junction of a pair of Zener diodes is connected between the emitter and collector of the bidirectional transistor so that the bidirectional transistor is protected regardless of the polarity of the power supply. Even if the polarity of the power supply applied to the bidirectional transistor is reversed due to switching, the voltage applied to the emitter collector is always limited to the Zener breakdown voltage, and overvoltage damage to the transistor can be prevented.

In addition, the Zener breakdown voltage is set to be higher than the power supply voltage, so no matter which polarity of the power supply is connected, a short circuit will not occur in the power supply, and therefore a protection circuit can be connected to bidirectional transistors without any problem. .

[Brief explanation of the drawing]

Fig. 1 is a motor drive circuit diagram showing an embodiment in which the present invention is applied to a two-phase switching type brushless motor, Fig. 2 is a waveform diagram showing the back electromotive force applied to the bidirectional transistor of Fig. 1, and Fig. 3 The figure is a circuit diagram showing a modification of the transistor protection circuit. In addition, in the symbols used in the drawings, 1...Hall element, 2, 3...Differential amplifier, 4...Differential switch circuit, 5...Reverse switch, ZD1, ZD2...
Zener diode, L _A , L _A ′, L _B , L _B ′...Coil, S1, S2... Power line, T3, T4...
...It is a bidirectional transistor.

Claims (1)

[Claims for Utility Model Registration] In order to bidirectionally energize motor excitation coils of each phase connected between power lines whose polarity can be reversed,
A bidirectional transistor whose collector-emitter is connected between the first and second excitation coils that divide the coil of each phase into two, and a bidirectional transistor whose collector-emitter is connected in series with opposite polarity to each other and connected in parallel between the collector-emitter of the above-mentioned transistors. Each is equipped with a pair of Zener diodes for overvoltage prevention and a forward/reverse switch that switches the polarity of the power line to change the direction of rotation of the motor, and the Zener voltage of the Zener diode is applied to the collector emitter of the bidirectional transistor. A forward/reverse drive circuit for a motor, characterized in that the voltage is lower than the withstand voltage and higher than the voltage between the power supply lines.