JPH0222626B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a phase control circuit for an AC commutator motor or the like used in a vacuum cleaner, and its purpose is to ensure power control through phase control.

As shown in FIG. 1, in a conventional phase control circuit, a motor 102 and a thyristor 103 are connected in series to an AC power source 101, and a negative resistance element 104 and a capacitor 105 are connected in series between the cathode and gate of the thyristor 103. A variable resistor 106 is connected to the capacitor 105 from the anode of the thyristor.

With the above configuration, the electric motor 102 is connected to the power source 101.
A charge is charged to the capacitor 105 through the variable resistor 106, and when the potential of the capacitor 105 exceeds a certain potential, the negative resistance element 104 becomes conductive, triggering the gate of the thyristor 103, and the thyristor 103 is turned on. variable resistance 1
When the resistance value of 06 is changed, the capacitor 10
The charging current to the capacitor 105 changes, and the potential rise time of the capacitor 105 changes. Therefore, the time to trigger the gate of the thyristor 103 changes, the phase at which the thyristor 103 is turned ON changes, the conduction angle of the motor flowing to the motor 102 changes, and the power control changes, thereby performing power control.

However, if the voltage itself of the power supply voltage 101 changes, for example if it becomes higher, the variable resistor 106
Since the current flowing through capacitor 1 increases,
The potential of thyristor 103 rises quickly, and the potential of thyristor 103
It turns on faster and the conduction angle of the current flowing through the load becomes larger. Therefore, the power of the load becomes large,
Furthermore, since the voltage is high, the peak value of the current flowing through the load is also high, resulting in even greater power. Second
The situation is shown in the figure, where the waveform of the initial load current I ₀ has a conduction angle θ ₀ and a peak value I ₀ , as shown by the solid line, but when the voltage is high, the conduction angle changes as shown by the broken line. Since the wave spreads to θ ₁ and the peak value also increases to I ₁ , the power becomes extremely large.

Conversely, when the voltage of the power supply 101 decreases, the current flowing through the variable resistor 106 decreases, and the phase of the trigger is delayed. Therefore, the conduction angle of the current flowing through the load becomes small, and the peak value itself becomes low, resulting in a very small power. If the voltage drop is significant, the potential of the capacitor 105 may not reach the trigger potential and the thyristor 103 may not turn on.

The present invention aims to eliminate the above-mentioned drawbacks of the conventional art and provide a control circuit whose power fluctuates little with respect to voltage fluctuations.Embodiments thereof will be described below with reference to the accompanying drawings.

In Fig. 3, electric motor 2 is connected to AC power source 1.
and a bidirectional thyristor 3 are connected in series, and a negative resistance element 4 and a capacitor 5 are connected in series between the cathode and gate of the thyristor 3.
FET, variable resistor 7, and second FET 8 are connected,
The gate of the first FET6 is between the variable resistor 7 and FET8, and the gate of the second FET8 is between the variable resistor 7 and the first
is connected between FET6.

From the above configuration, when the power supply 1 is in a positive cycle, the charging current to the capacitor 5 flows from the anode side of the thyristor 3 to the first FET 6, the variable resistor 7, and the second
The current flows through FET 8, and since the gate of the second FET 8 is higher than the drain voltage, the current flows freely, and the gate of the first FET 6 protrudes from below the variable resistor 7, so the potential is more negative than the source, and the current flows. 1st
is limited by FET6. The gate voltage V _GS6 of the first FET 6 is V _GS6 =I·R ₇ I: current flowing through the FET 6 R ₇ : resistance value of the variable resistor 7.

Conversely, when power supply 1 is in a negative cycle, the second
FET8 limits the current and FET8 gate voltage
V _GS8 becomes V _GS8 = -I・R ₇ , and the same voltage is applied to both the positive and negative sides as V _GS8 = V _GS6 .

When the voltage increases and the current I tries to increase, the gate voltage increases further in the negative direction according to the above equation, and this works in the direction of decreasing the current, so the current does not increase after all. Conversely, when the voltage decreases and the current I attempts to decrease, the gate voltage decreases according to the above equation, which works in the direction of increasing the current, and in the end the current does not decrease but remains at a constant value. Even if the voltage fluctuates in this way, the current flowing through the FET and charging the capacitor 5 always remains constant, the phase that triggers the thyristor 3 is always constant, and the conduction angle of the load current flowing through the motor 2 does not change. As shown in FIG. 4, as the voltage of the load current increases, the peak value increases from I ₀ to I ₁ , but the conduction angle remains the same as θ ₀ =θ ₁ and the power fluctuation is kept small.

In order to change the load current by changing the conduction angle θ, the charging current can be changed by changing the resistance value of the variable resistor 7, and the power can be controlled by the variable resistor 7.

As described above, according to the present invention, it is possible to realize, with a simple configuration, a control circuit that suppresses power fluctuations in the load to a small extent even when the voltage fluctuates, and the effect thereof is extremely large.

In this embodiment, the charging current to the capacitor is taken from the anode of the thyristor, but it may of course be taken from between the power supply and the motor.

[Brief explanation of drawings]

Figure 1 is a phase control circuit diagram in a conventional example;
3 is a diagram illustrating the load current, FIG. 3 is a phase control circuit diagram in an embodiment of the present invention, and FIG. 4 is a diagram illustrating the load current. 1... AC power supply, 2... Load, 3... Bidirectional thyristor, 5... Capacitor, 6, 8...
FET, 7...variable resistance.

Claims (1)

[Claims] 1 A load and a bidirectional thyristor are connected in series to an AC power supply, the gate trigger of this thyristor is performed by the charge charged in the capacitor, and the conduction angle of the current flowing to the load is changed by changing the current charging the capacitor. In the phase control circuit, the variable charging circuit for the capacitor is composed of a series circuit of a first FET, a variable resistor, and a second FET, and the gate of the first FET is connected to the connection between the second FET and the variable resistor. the gate of the second FET is connected to the connection between the first FET and the variable resistor,
A phase control circuit in which a series circuit of the variable charging circuit and a capacitor is connected in parallel with the AC power supply or the bidirectional thyristor.