JPH0218037B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a motor drive circuit that enables reversible operation of the motor.

Structure of a conventional example and its problems FIG. 1 shows a conventional motor drive circuit. In the figure, reference numerals 1, 2, 3, and 4 are transistors for reversibly driving a motor 9, which are bridged to each other.
Reverse conducting diodes 5, 6, 7 and 8 are connected between the emitter and collector of each transistor to reversely conduct the respective transistors. 9 is a reversibly controlled electric motor. transistor 1,
2, 3 and 4 each repeat ON-OFF,
The configuration is such that voltage is applied to the motor to drive it in relation to the ON-OFF cycle and the O time.

The operation of the conventional example configured in this way will be explained below using FIG. 2. FIG. 2 is a timing diagram for explaining the operation of FIG. 1, and shows the case where the motor is driven in one direction. When driving the motor 9 in one direction, as shown in Fig. 2, the ON and OFF times of transistors 1 and 4 are controlled to obtain an average voltage Vm of Vm=T _ON /T _ON +T _OFF ×V (1) to the electric motor 9. Here V
is the power supply voltage in the circuit of FIG. During the time when transistor 1 is ON, a current flows through each transistor as i ₁ in relation to the electrical time constant of motor 9. Transistors 1 and 4
During the OFF time, a counter electromotive force current i ₂ due to the inductance of the motor 9 flows through the reverse conduction diodes 7 and 6 as shown in the figure. Therefore, the motor current i _n of the motor 9 is the sum of i ₁ and i ₂ as shown in FIG. The collector voltage VCE 3 of one-way transistor ₃ is as shown in FIG.
At the same time as turning on, the voltage rises instantaneously from near zero potential to the power supply voltage V.

Normally, as a characteristic of a transistor, there is a capacitance C _OB between the collector and the base, and the C _OB becomes larger as the transistor handles a larger amount of power. Therefore, the capacitance between the collector and base of transistor 3 in Fig. 1 is
When VCE ₃ rises momentarily due to C _OB , a current that charges C _OB flows from the collector to the base. As a result, the current flowing into the base is multiplied by the DC current amplification factor and flows into the collector current. As shown in FIG. 2, this peak collector current i _p flows only for the time T〓 when C _OB finishes charging. That is, i _p ≒h _fe ×C _OB ×d/dtVCE ₃ (2). Here, h _fe indicates the DC current amplification rate of the transistor 3. As shown in equation (2), the maximum value i _p of the collector current instantaneously flowing through transistor 3 is determined by the DC current amplification factor h _fe and the capacitance between the collector and base C _OB
and is proportional to the amount of change in collector voltage d/dt×VCE ₃ .

Normally, the value of i _p shown in equation (2) is larger than the maximum collector current shown in the ASO curve of the transistor. Therefore, in the conventional circuit shown in Fig. 1, due to the peak collector current i _p shown above, a transistor with a current capacity much larger than the armature current flowing in a normal motor is required, and the cost of the transistor used is low. It had the disadvantage that it was expensive. Further, the same problem occurs when the electric motor 9 is driven in the other direction, and the same drawbacks as described above are caused.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned drawbacks of the conventional circuit and provides a motor drive circuit that is cheaper than the conventional circuit and uses a transistor with a current capacity approximately equal to the armature current of the motor used.

Structure of the Invention The present invention has four transistor switch circuits each having a reverse conduction diode between an emitter and a collector, two impedance circuits, and a transistor reverse bias circuit, and the impedance circuit is provided in the collector circuit of the transistor switch circuit. This configuration has the unique effect of limiting the peak current of the transistor to a small value, making the circuit configuration inexpensive and highly reliable.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 shows a motor drive circuit in an embodiment of the present invention.

In Figure 3, 10, 11, 12 and 13 are reverse conducting diodes 1 at the emitter and collector, respectively.
The transistors have transistors 4, 15, 16, and 17, and have a bridge configuration. Impedance circuits 18 and 19 are connected to collector circuits of transistors 12 and 13, respectively. In this embodiment, the impedance circuit is composed of an inductor. Reference numeral 20 denotes a motor whose drive is controlled, which is connected to the emitter circuit of transistors 10 and 11, and is configured to be capable of reversible operation. V is the power supply voltage determined by motor 20. The bases of the transistors 1 and 13 have reverse bias circuits 21 and 22, respectively, and are connected to the negative potential -V _B through resistors R ₁ and R ₂ . FIG. 4 is a timing diagram for explaining the motor drive circuit of FIG. 3, which is an embodiment of the present invention. In FIG. 3, when the motor 20 is driven in one direction, the transistors 10 and 13 are controlled ON-OFF as shown in FIG. 4 to provide the motor with the average voltage shown in equation (1). When the transistor 10 is turned on, the emitter voltage of the transistor 10 instantaneously rises to V as shown in FIG. Immediately before the transistor 10 is turned on, a current flows through the reverse conduction diode 16 as shown in FIG. 4, so the emitter of the transistor 10 is kept at zero potential.

Therefore, the emitter of transistor 10 instantaneously rises from zero potential to the power supply voltage. Since the inductor 18 is connected to the collector circuit of the transistor 12, the transistor 12 is connected as shown in FIG.
The collector voltage _VCE12 does not instantaneously become the power supply voltage, but rises along a curve determined by the inductor 18, the collector-base capacitance _COB12 of the transistor 12, the base resistance of the transistor 12, the resistance _R1 , and the negative potential _-VB . . At this time, the peak current i _p12 flowing through the transistor 12 is i _p12 =h _fe12 ×C _O12 ×d/dtVCE ₁₂ ×1/K (3), similar to equation (2). Here, h _fe12 is the DC current amplification factor of the transistor 12. K is a constant determined by the resistance _R1 and the negative potential _-VB . The value of K takes a larger value as the value of resistor R ₁ becomes smaller or the value of -V _B becomes larger.
It is determined by the switching characteristics of the transistor 12. From equation (3), in order to reduce the value of the peak current i _p12 , the change in d/dtVCE ₁₂ , that is, the voltage applied to the collector of the transistor 12, must be reduced or K
It turns out that it is better to increase the value of . Inductor 1
8 has an integral effect, so the value of d/dtVCE ₁₂ can be made small as shown in FIG. Further, if the rise time of this peak current i _p12 is T〓, the value of i _p12 can be further reduced by selecting a value of the inductor 18 that has a high impedance with respect to this T〓.

Next, when driving the motor 20 in the other direction, the peak current of the transistor 13 can be reduced in the same way as above by using the inductor circuit 19, the resistor R ₂ connected to the base of the transistor 13, and the negative potential -V _B. .

Furthermore, FIG. 5 shows an embodiment for speeding up the switching operation of the drive circuit of the embodiment of FIG. In FIG. 5, reverse bias circuits 23 and 24 are provided at the bases of transistors 10 and 11, respectively, and resistors R ₃
and R ₄ and reverse bias voltages V ₁₀ and V ₁₁ are connected as shown in the figure. This resistance and the reverse bias voltage reduce the fractional carrier storage time at the bases of transistors 10 and 11, allowing faster switching. Therefore, it goes without saying that the drive circuit shown in FIG. 5 can also reduce the peak currents of the transistors 12 and 13 as in the embodiment shown in FIG.

As described above, according to this embodiment, by providing a four-transistor bridge circuit having a reverse conduction diode between the emitter and collector, two inductor circuits, and a reverse bias circuit, the non-operating transistor during switching of the transistor is provided. This has the effect of being able to control the peak collector current to a small value, improving the reliability of the drive circuit, and reducing costs.

In the embodiments shown in FIGS. 3 and 5, the impedance circuit is an inductor, but other elements may be used as long as they have a value sufficiently smaller than the impedance of the motor. Furthermore, it goes without saying that this embodiment can be applied to an AC circuit or a bridge circuit composed of three or more phases. Further, the transistor can be either a normal single type or a Darlington type, and a thyristor or other switch element may also be used.

Effects of the Invention As described above, the present invention has a circuit configuration in which an impedance circuit and a bias circuit are added to a transistor bridge circuit, thereby providing a more reliable and inexpensive electric motor drive circuit than conventional ones, and its practical effects. is a great thing.

[Brief explanation of drawings]

FIG. 1 is a conventional motor drive circuit diagram, FIG. 2 is a timing diagram for explaining FIG. 1, FIGS. 3 and 5 are motor drive circuit diagrams according to an embodiment of the present invention, and FIG. The figure is a timing diagram for explaining FIGS. 3 and 5. 10, 11, 12, 13...transistor, 1
4, 15, 16, 17...Reverse conduction diode, 1
8, 19... Impedance circuit, 20... Electric motor, 21, 22, 23, 24... Reverse bias circuit.

Claims (1)

[Claims] 1. First, second, third, and fourth transistors each having a reverse conduction diode between an emitter and a collector, the collector of the first transistor being connected to the collector of the second transistor and a motor. The emitter of the third transistor is connected to the high potential side of the power source that drives the motor, the emitter of the third transistor is connected to the emitter of the fourth transistor and the low potential side of the power source, and the emitter of the first transistor is connected to the high potential side of the power source that drives the motor.
The emitter of the second transistor is connected to the other terminal of the motor and the input of the second impedance circuit, and the output of the first impedance circuit is connected to the collector of the third transistor, the output of the second impedance circuit is connected to the collector of the fourth transistor, and the bases of the third and fourth transistors are reverse biased with respect to their respective emitters. A motor drive circuit having a circuit. 2. The motor drive circuit according to claim 1, wherein the bases of the first and second transistors have a reverse bias circuit with respect to the emitters of the respective transistors.