JPS6118769B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for limiting excessive inrush current to the load at the start of energization when controlling energization from an AC power source to a low impedance load using a bidirectional three-terminal thyristor. It is related to circuits.

Generally, when AC voltage is applied to a load with low impedance, such as when charging a capacitor directly from the power supply, such as in a switching power supply, or when a smoothing capacitor is connected to the secondary side of the transformer, , At the beginning of application, an excessive inrush current flows, which may destroy circuit elements or cause noise disturbances.

FIG. 1 is a circuit diagram showing a conventional current limiting circuit employed in a bidirectional three-terminal thyristor in order to limit the excessive inrush current at the start of energization as described above.

Please refer to FIG. Between the AC power supply 1 and the load 2 to be supplied with power from the power supply, bidirectional three-terminal thyristors 3 and 6, an operating switch 4, resistors 5, 7, 8, and 13, and a diode 9 are provided.
, a relay 10 and its contacts 12, and a capacitor 11 are connected as shown. Bidirectional 3-terminal thyristor (hereinafter sometimes simply referred to as 3-terminal thyristor) 3 is a main 3-terminal thyristor, and 6 is a secondary 3-terminal thyristor.

Now, in FIG. 1, the contact 12 is a contact that closes when the relay 10 operates, and is initially open.
When the AC power source 1 starts supplying current to the load 2 through the main three-terminal thyristor 3, the operation switch 4 is first passed through, thereby making the sub three-terminal thyristor 6 conductive. Therefore, a current limited by the resistor 7 flows to charge the load 2.
On the other hand, capacitor 1 is connected through resistor 8 and diode 9.
1 is charged, and when the capacitor 11 reaches a predetermined charging pressure after a certain period of time, the relay 10 operates, the relay contact 12 closes, and the main 3-terminal thyristor 3 becomes conductive, shifting to normal operation. Here resistance 5,1
3 is for limiting the trigger current of each three-terminal thyristor. This method uses two large switch elements, three-terminal thyristors, which are difficult to mount on printed circuit boards due to complicated heat dissipation and mounting methods.
It is disadvantageous in terms of cost. In addition, if the main three-terminal thyristor 3 does not conduct because the contacts 12 do not close due to a failure in the relay 10 or the like, there is a drawback that the large resistor 7 of several tens of W becomes overloaded and easily burns out. On the other hand, as a method for turning on an AC power source, a method is used in which the zero phase of an AC sine wave is detected and switched on, but this method does not have the above-mentioned effect of limiting the inrush current.

This invention was made in order to overcome the drawbacks of the conventional circuit as described above, and an object of the invention is to use small components that can be mounted on a printed circuit board, which is advantageous in terms of cost. With,
An object of the present invention is to provide a bidirectional three-terminal thyristor capable of opening and closing an AC power supply without generating an excessive rush current.

The gist of the configuration of this invention is that in a bidirectional three-terminal thyristor that controls current flow from an AC power source to a load, a charging circuit for a first capacitor and a second capacitor is connected between its input terminal and output terminal. At the same time, a discharge circuit for the capacitor including a second capacitor and an electro-optical conversion element is provided, and the gate terminal and the input terminal of the three-terminal thyristor are further connected via a photo-electric conversion element that should receive light from the electro-optical conversion element. The two capacitors are charged in series through a charging circuit during the rising portion of the sine wave voltage from the AC power supply, and the second capacitor is discharged through the electro-optical conversion element during the falling portion, causing the electro-optical conversion element to emit light. When the photoelectric conversion element conducts in response to the light emission, the bidirectional three-terminal thyristor is triggered to conduct, and by adjusting the charging voltage of the capacitor, the bidirectional three-terminal thyristor in the voltage sine wave is The point is that it is possible to control the conduction phase angle of the thyristor and limit the rush current to the load.

Next, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the same figure, an operating switch 4, a resistor 5, a diode 2
1 to 24, capacitors 25 and 26, Zener diode 27, resistors 28 and 29, electro-optical conversion element 30, photoelectric conversion element 31, and switch 3
2 are connected as shown in the figure, and when the electro-optical conversion element 30 emits light, the photo-electric conversion element 31 receives the light.

Now, in FIG. 2, a charging current flows through the diode 22, capacitors 25, 26, resistor 28, and diode 23 in the positive half thyristor of the sine wave from the AC power source 1, charging each capacitor.
Compared to the capacitance of capacitor 25, capacitor 2
If the capacitance of the capacitor 6 is set to a sufficiently small value, the capacitor 26 will be charged to the Zener voltage Vz of the Zener diode 27 at the rising edge of the half-thyristor of the sine wave. However, in the following explanation, the voltage drop across the diode will be ignored. When the sine wave falls and the peak value of the sine wave becomes lower than the sum of the charging voltages of the capacitors 25 and 26, the charge in the capacitor 26 is discharged through the path of the resistor 29 and the electro-optical conversion element 30. starts, and the electro-optical conversion element 30 emits light due to the discharge current. Therefore, the photoelectric conversion element 31 receives light and becomes conductive, so the resistor 5
A trigger current flows through the gate terminal of the bidirectional three-terminal thyristor 3, causing the thyristor 3 to conduct. In the next half cycle of the sine wave, diode 2
4. Charging operation through capacitors 25, 26, resistor 28, and diode 21 and discharging operation through capacitor 26, resistor 29, and electro-optical conversion element 30 are performed in the same way, but at this time, capacitor 25 is connected to the previous half thyristor. Bidirectional 3-terminal thyristor 3 is charged to a higher voltage value than when
The peak value of the sine wave at the time of conduction also becomes high. The main points of the charging/discharging relationship in the above operation will be explained in detail with reference to FIG.

FIG. 3 is a diagram showing a sinusoidal voltage waveform from the AC power supply 1 and a change in the potential Va at point a in FIG. If switch 4 in FIG. 2 is turned on at time _S1 in FIG. 3, capacitors 25 and 26 are charged by the sine wave voltage as described above, but
Charge voltage V ₁ of capacitor 25 and capacitor 26
After the time _S2 when the sinusoidal voltage drops to the sum of the charging voltages Vz (equal to the Zener voltage of the Zener diode 27), that is, ( _V1 + Vz), the capacitor 26 starts discharging. Lightning conversion element 3
0 emits light, and upon receiving the light, the photoelectric conversion element 31 becomes conductive, thereby making the three-terminal thyristor 3 conductive. As a result, a voltage approximately equal to (V ₁ +Vz) is applied to the load 2. When the next half cycle of the sine wave begins, capacitors 25 and 2 are connected again.
6 has been charged and the charging voltage of the capacitor 25 has now reached V ₂ .Then, the electro-optical conversion element 30 emits light and the 3-terminal thyristor 3 becomes conductive because the sine wave voltage is (V ₂ +Vz) after the time S ₂ '. In this way, the capacitor 26 is repeatedly charged and discharged, but the capacitor 25 has no chance of discharging and is being charged. Therefore, if the value of the resistor 28 is selected so that the capacitor 25 is gradually charged, the peak value at the time when the three-terminal thyristor 3 becomes conductive will also gradually increase. As a result, the voltage applied to load 2 is the zener voltage Vz
can be set arbitrarily depending on how to choose, and therefore the load applied voltage can be limited to a value that matches the impedance of load 2 and the allowable inrush current value.
Moreover, the value can be gradually increased.

Next, returning to FIG. 2, the explanation will be continued. As described above, if the switch 32 is closed after a certain period of time after the operation switch 4 is turned on, the aforementioned control circuit is separated from the power supply circuit, and the three-terminal thyristor 3 performs steady operation. At times, a capacitor (not shown) in the load 2 is charged to a sufficient value, so that no excessive rush current flows to the load 2. Note that the control for closing the switch 32 at an appropriate time may be performed by any suitable means. For example, the relay 10 in FIG.
It is also possible to directly imitate the point that the contact point 12 is closed after the time required for charging.
Although the photoelectric conversion element 31 needs to be bidirectionally conductive, FIG. 4 shows a connection example in which an element that conducts only in one direction, such as a photodiode or a phototransistor, is used.

FIG. 4 is a circuit diagram showing another embodiment of the invention. The difference between the circuit shown in the figure and the circuit shown in Fig. 2 is that a resistor 33 is added in parallel with the capacitor 25, so that the capacitor 25
The phototransistor 41 conducts only in one direction as a photoelectric conversion element.
In order to make the gate circuit of the three-terminal thyristor 3 bidirectional, diodes 42 to 45 are connected as shown, and a resistor 46 is added as shown. This is added for the purpose of reducing the voltage applied to the phototransistor 41, which has a small breakdown voltage, by dividing the voltage together with the resistor 5. The differences are as described above, and the basic mode of operation is the same as that of the embodiment shown in FIG.

In each of the embodiments shown in FIGS. 2 and 4, the circuit configuration is such that the bidirectional three-terminal thyristor 3 is conductive in each positive and negative half cycle of the sinusoidal AC voltage from the power supply. If the load is only a capacitor load such as a switching control power supply, conduction can be made only during a half cycle of the sine wave. In this case, in FIG. 2, diodes 21 and 24 are removed, the circuit in which they were inserted is opened, and the diode 2
In the circuit where No. 3 is inserted, it is preferable to remove the diode 23 and short-circuit it. In the circuit shown in Figure 4,
In addition to the above, diodes 42 and 45 are removed to open the circuit, and diodes 43 and 44 are removed to short the circuit. In addition, if a load such as a large transformer is placed in parallel, when the switch 32 closes and the 3-terminal thyristor 3 starts steady operation, a saturation current will flow due to the biased magnetization of the transformer coil, so the various diodes mentioned above are added. It is necessary to keep the bidirectional three-terminal thyristor 3 conductive in both positive and negative half cycles.

As explained above, according to the present invention, when a bidirectional three-terminal thyristor is used to supply power to a load including a large-capacity capacitor, the inrush current can be arbitrarily controlled to a sufficiently small value. Although the number of parts in the control circuit is slightly increased compared to the conventional one, it is made up of small parts that can be mounted on a printed circuit board, and the control circuit is hardly energized during normal operation, so the cost is low. It is inexpensive and has excellent operational reliability. In addition, even if the control circuit were to malfunction, it would only make the bidirectional three-terminal thyristor more likely to fail in terms of reliability, and it has the advantage that there is no danger of it leading to a burnout accident as in the case of conventional technology. .

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of an inrush current limiting circuit at the start of energization conventionally adopted in a bidirectional three-terminal thyristor, Fig. 2 is a circuit diagram showing an embodiment of the present invention, and Fig. 3 2 is a diagram showing the waveform of an alternating current voltage and the potential change at point a in FIG. 2, and is a diagram for explaining the main points of the operation of the embodiment of FIG. 2. FIG. FIG. 4 is a circuit diagram showing another embodiment of the invention. In the figure, 1 is an AC power supply, 2 is a load, 3 is a bidirectional three-terminal thyristor, 4 is an operating switch,
5 is a resistor, 6 is a bidirectional three-terminal thyristor, 7 and 8 are each a resistor, 9 is a diode, 10 is a relay, 11 is a capacitor, 12 is a contact of the relay 10, 13 is a resistor, 21 to 24 are each a diode, 25 and 26 are capacitors, 2
7 is a Zener diode, 28 and 29 are resistors, 30 is an electro-optical conversion element, 31 is a photoelectric conversion element, 32 is a switch, 33 is a resistor, 41 is a phototransistor, 42 to 45 are diodes, 46
indicates resistance.

Claims (1)

[Claims] 1. In a bidirectional three-terminal thyristor that is to control energization from an AC power supply to a load, a first capacitor and a Second
A charging circuit comprising a capacitor and a starting operation switch is connected, a discharging circuit for the capacitor including the second capacitor and an electro-optical conversion element is provided, and a gate terminal of the bidirectional three-terminal thyristor is connected. and an input terminal via a photoelectric conversion element that receives light from the electro-optical conversion element, and when the operation switch is turned on, the charging circuit The second capacitor charges both capacitors in series through the capacitor until it reaches a predetermined charging completion voltage value, and in the falling part of the sine wave voltage, the peak value becomes the sum of the charging voltage values of the two capacitors. When the voltage drops to below, the second capacitor starts discharging through the discharge circuit, causing the electro-optical conversion element to emit light, and the photo-electric conversion element receiving the light becomes conductive, thereby causing the By triggering the bidirectional three-terminal thyristor to conduct, and adjusting either or both of the charging voltage value of the first capacitor and the predetermined charging completion voltage value of the second capacitor,
An AC load control circuit using a bidirectional three-terminal thyristor, characterized in that a conduction phase angle of the bidirectional three-terminal thyristor in the voltage sine wave can be controlled.