JPH0521998Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching-driven two-phase half-wave drive type non-commutator motor drive circuit.

Commutatorless motors are usually two-phase full-wave, three-phase half-wave,
Three-phase full-wave and four-phase half-wave drives were common. The reason why the cost-effective two-phase half-wave drive was not adopted is that during one rotation of the rotor, there are at least two points (so-called dead points) where the drive torque becomes zero. However, in recent years, improvements have been made to the magnetization of the magnets on the rotor side, the shape of the winding yoke on the stator side, etc., and motors that overcome the above-mentioned problems have been put into practical use.

A typical drive circuit for a two-phase half-wave drive motor includes power transistors Tr ₁ and Tr ₂ connected in series to drive windings L ₁ and L ₂ and connected to the output terminal of a Hall element H, as shown in Figure 1. detected transistor
A method in which switching is performed using Tr ₃ and Tr ₄ , or a method using a Hall IC as shown in FIG. 2 is known.

However, in the case of the drive circuit shown in FIG. 1, if the linear output of the Hall element is directly sent to the power transistor, the power transistor will suffer from large power loss, which will cause an increase in cost. The circuit shown in FIG. 2 takes this point into consideration and uses a switching type Hall IC, which sends a rectangular wave signal to the power transistor to alternately turn it on and off. However, in the case of drive using a square wave, a spike voltage is generated due to electromagnetic energy charged in the drive winding when the phase is switched.

This invention effectively suppresses this spike voltage,
The purpose of this is to enable the use of low-grade components and provide an inexpensive drive circuit.

FIG. 3a is a model of the above-mentioned contents. Here, Tr ₁ and Tr ₂ are power transistors,
L ₁ and L ₂ are drive windings, SW is a changeover switch, and R is a base resistor for driving the power transistors Tr ₁ and Tr ₂ . Now, when the switch SW is switched from the power transistor Tr ₁ side to the power transistor Tr ₂ side, a spike voltage as shown in FIG. 3b is generated at the point t=o at that moment. This spike voltage is expressed as e=Ldi/dt, and increases as the motor becomes larger. Therefore, although the power transistor may have small power loss, it is necessary to use a power transistor with high withstand voltage.

As a countermeasure against this, a capacitor _C1 is usually placed between the collector-emitter of the power transistor _Tr1 and the collector-emitter of the power transistor _Tr2 as shown in Figure 4a.
and _C2 . This will almost always solve the problem when the electromagnetic energy is small, but if this method is used when the electromagnetic energy is large, the spike voltage will not be as small as expected if the capacitor capacity is relatively small (Figure 4b), and if the capacity is increased, the capacitor will continue to be charged even after t = 0, and this current will brake the motor's rotation and increase current consumption.
(Fig. 4c) This invention improves the above-mentioned shortcomings.
The following description will be given with reference to the figure.
The driving circuit shown in the figure is a model of the driving circuit using the present invention. That is, Fig. 5a is a model of a driving circuit in which a bidirectional capacitor _C3 is connected between the bases of _Tr1 and _Tr2 shown in Fig. 2. In Fig. 5a, _Tr1 and _Tr2 are power transistors, _L1 and _L2 are power transistors.
The drive windings are connected to the collectors of _Tr1 and _Tr2, respectively. SW is a switch consisting of a switching type Hall IC, a transistor, a resistor, and a diode circuit as shown in Figure 2. R is a base resistor.
These configurations are the same as those of the conventional device. The feature of this invention is that a bidirectional capacitor _C3 is connected between the bases of the power transistors _Tr1 and _Tr2 .

The operation will be explained below.

First, considering the moment t=o when the Hall IC that constitutes the switch SW detects a change in magnetic flux and switches the current flow from the base side of the power transistor Tr ₁ to the base side of the power transistor Tr ₂ , the bidirectional capacitor Since _C3 is provided, the power transistor _Tr1 is not cut off immediately.

In other words, power transistor Tr ₁ has the power supply + side (not shown) → base resistor R → switch SW → bidirectional capacitor C ₃ → base of power transistor Tr ₁ , which is related to the time constant of R×C ₃ (gradually decreasing). ) current flows, and the current flowing through the drive winding _L1 also gradually decreases. The current flowing through this drive winding _L1 and the voltage applied thereto are shown in FIG. 5b. In addition,
The dotted line in the figure shows the current of the conventional one without the bidirectional capacitor _C3 . Even after the switch SW is switched in this way, the power transistor Tr ₁ does not turn off immediately, and a current that gradually decreases according to the R×C ₃ time constant flows through the drive winding, and this gradual decrease (the line in the figure (as di/dt can be made small), it is possible to control the generation of spike voltage (e=Ldi/dt). On the other hand, in the conventional type, the current changes rapidly as shown by the dotted line in Figure 5b.
The spike voltage is large because di/dt is large.

Note that from the moment the switch SW performs the above-described operation, current is also supplied to the base of the power transistor _Tr2 , so no delay in the rise characteristic occurs.

Furthermore, since the current input to the bidirectional capacitor C ₃ is the base current of the power transistors Tr ₁ and Tr ₂ , it is smaller than the collector current, and the capacitance of the bidirectional capacitor C ₃ can be reduced.
In this case as well, the spike voltage can be sufficiently controlled.
Therefore, it can be downsized.

Furthermore, the resonance phenomenon between the drive windings L ₁ and L ₂ and the capacitors C ₁ and C ₂ as shown in FIG. 4 does not occur in the present invention.

As described above, in this invention, it is possible to use a power transistor with a low withstand voltage without affecting the motor in any way.
A cheap and efficient circuit can be obtained. It goes without saying that a similar result can be obtained by using a polar capacitor connected in series with reversed polarity in place of the bidirectional capacitor.

[Brief explanation of the drawing]

Figures 1 and 2 are drive circuit diagrams of a conventional two-phase half-wave drive type non-commutator motor, Figure 3a is the drive circuit diagram of a conventional two-phase half-wave drive type non-commutator motor,
FIG. 3b is a diagram showing the state of spike voltage generation in the same circuit; FIG. 4a is a circuit diagram with spike voltage control means;
Figures b and c are diagrams showing the state of spike voltage generation in the same circuit, Figure 5a is a circuit diagram modeling the drive circuit of the present invention, and Figure 5b is the current flowing through the drive winding and spikes in the same circuit. FIG. 3 is a diagram showing a voltage generation state. L ₁ , L ₂ ... Drive winding, Tr ₁ , Tr ₂ ... Switching element (transistor), C ₃ ... Capacitor.

Claims (1)

[Scope of utility model registration request] A two-phase half-wave drive non-commutator motor driven by switching is characterized in that a bidirectional capacitor is connected between each input of a plurality of switching elements whose output sides are connected in series with a plurality of drive windings. Commutatorless motor drive circuit.