JPH02276461A - Phase control circuit - Google Patents

Abstract

PURPOSE:To control the firing angle of switching element safely independent of AC source voltage fluctuation by connecting a second bidirectional trigger element in parallel with a series circuit of a variable resistor and a capacitor. CONSTITUTION:A bidirectional trigger element T3 is connected in parallel with a series circuit of a variable resistor VR and a capacitor C. The trigger element T3 has relatively high breakover voltage, and when a voltage higher than the breakover voltage is applied after conduction conducting state is maintained with a predetermined ON resistance. In a range where the voltage of AC power source AC is higher than the breakover voltage, predetermined voltage is applied across the series circuit of the variable resistor VR and the capacitor C even if the source AC voltage fluctuates. Firing angle of a switching element T1 is controlled based on a time constant which is determined by the variable resistor VR and the capacitor C so that fluctuation of load current is suppressed.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention relates to a phase control circuit that performs phase control by controlling the firing angle of a bidirectional switching element connected in series to an AC power source via a load. It is related to.

[Conventional technique @1 An example of a conventional phase control circuit is shown in FIG. 4. In this phase control circuit, a bidirectional switching element (for example, a triac) T+ is connected in series to an alternating current power supply AC via a load I, and this bidirectional switching element T is connected to half of the alternating current power supply AC by a gate circuit 1. By controlling conduction every cycle, the phase of the current supplied to the load is controlled.

Here, the gate circuit 1 includes a capacitor C that is charged and discharged every half cycle of the AC power source AC, and a bidirectional switching element T that adjusts the current supplied to the capacitor C.
a variable resistor VR for controlling the firing angle of the above-mentioned capacitor C;
When the voltage across T rises above the break\over voltage, the capacitor's charge is discharged and the bidirectional switching element T is activated.

It is composed of a bidirectional trigger element T2 that allows a gate current to flow through the gate. Note that in FIG. 4(a), a diac (bidirectional diode) is used as the trigger element T2, and in FIG. 4(b), a 5BS (silicon circular switch) is used. Further, in this gate circuit 1, a resistor R is connected in series with the variable resistor VR to regulate the maximum firing angle at which the switching element T becomes conductive.

In this phase control circuit, the AC power supply A shown in FIG.
During a half cycle of C, capacitor C is charged via resistor R and variable resistor VR as shown in FIG. 6(b). When the voltage across the capacitor C exceeds the breakover voltage of the trigger element T2, the trigger element T2 becomes conductive. Therefore, a gate current is supplied to the switching element T1, the switching element T2 is turned on, and power is supplied to the load. Note that the charge in the capacitor C is discharged by conduction of the trigger element T2. Then, when the alternating current power supply AC enters the next half cycle, voltage is no longer applied across the switching element T1, and therefore the switching element T1 returns to the non-conducting state. Then, during the next half cycle, the capacitor C is charged in the opposite direction, and the switching element T1 is fired in the same manner as described above. At this time, the voltage and current of the load are shown in Fig. 6 (e) and (d).
), the load current flows during the period from when the gate of the switching element T is turned off until the start of the dog half cycle. In other words, the capacitor C is charged in the forward and reverse directions every half cycle of the AC power supply AC, and the switching element T1
Switching. Here, the charging time constant of the capacitor C is changed by the value of the variable resistor VR, and the firing angle of the switching element T is controlled to increase or decrease the power supplied to the load. Also, Fig. 4 (a), (b)
The phase control circuits shown in FIG. 4 (
The breakover voltage of the bidirectional switch that is the trigger element T2 in a) is generally about 30V, and the breakover voltage of the SBS that is the trigger element T2 in the same figure (I]) is I
The only difference is that it is below OV. Note that the SBS is equipped with a gate.

[Problem to be solved by the invention 1 By the way, in the above phase control circuit, the switching elements T,
The firing angle, ie, the conduction period of the trigger element T2, is determined by the charging time of the capacitor C. Therefore, when the voltage of the AC power source AC changes, the charging voltage of the capacitor C also changes. For example, if the voltage of the AC power source AC drops as shown in Figure 6(b)(a), not only will the voltage applied to the switching element T drop, but it will also take time to charge the capacitor C. As a result, the breakover operation of the trigger element T2 is delayed as shown in (b) of the same figure, and therefore, as shown in (e) of the same figure, the time for supplying power to the load current is shortened, and the load current is significantly reduced. . Conversely, if the voltage of the AC power supply increases as shown in Figure 2 (a), the load current will increase significantly as shown in Figure 2 (e) for the exact opposite reason. .

That is, when a voltage fluctuation of the alternating current power supply/AC occurs, a larger fluctuation in the load current occurs than the voltage fluctuation of the alternating current power supply AC. For example, when the load is an illumination lamp and the voltage fluctuation of the alternating current power supply AC occurs as described above, there is an inconvenience that the lamp flickers.

The present invention has been made in view of the above points, and its purpose is to be able to stably control the firing and angle of the switching element without being affected by voltage fluctuations of the AC power supply. An object of the present invention is to provide a phase control circuit.

[Means for Solving Problem 1] In order to achieve the above object, the present invention provides a bidirectional switching element connected in series to an AC power source via a load,
This bidirectional switching element is equipped with a gate circuit that controls conduction every half cycle of the AC power supply, and a capacitor that is charged and discharged every half cycle of the AC power supply. a variable resistor for controlling the firing angle of the bidirectional switching element; and a first variable resistor for discharging the charge in the capacitor and causing a gate current to flow through the bidirectional switching element when the voltage across the capacitor rises above the breakover voltage. The gate circuit is composed of a bidirectional trigger element and a bidirectional trigger element of tIIJ2 connected in parallel to both ends of a series circuit of a variable resistor and a capacitor.

[Function 1] As described above, the present invention connects the second bidirectional trigger element in parallel to both ends of the series circuit of the variable resistor and the capacitor, so that even if the voltage of the AC power supply fluctuates, the gate circuit remains stable. The voltage across the variable resistor and the capacitor can be maintained at a substantially constant voltage by the second bidirectional trigamma chain;
As a result, it is not affected by voltage fluctuations of the AC power supply.
This makes it possible to stably control the firing angle of the switching element.

[Example 1 An embodiment of the present invention is shown in FIGS. 1 to 3.

The basic configuration of this embodiment is the same as the conventional phase control circuit described above, and in this embodiment, a bidirectional trigger element T is connected in parallel to both ends of a series circuit of a variable resistor VR and a capacitor C. It has characteristics.

22, the trigger element T3 exhibits the characteristics shown in FIG. 4,
The breakover voltage V BOI of this trigger element T
t V BON is a relatively high value, and if a voltage higher than the breakover voltage continues to be applied after conduction, the conduction state is maintained with a predetermined on-resistance.

Therefore, if this trigger element T is connected in parallel to both ends of a series circuit consisting of a variable resistor VR and a capacitor C, the AC power supply will be activated in the range where the voltage of the AC power supply AC is equal to or higher than the breakover voltage of this trigger element T. Regardless of fluctuations in the AC voltage, a predetermined voltage is applied across the variable resistor VR and the capacitor C when the trigger element T is conductive.

Note that a diac is used as the trigger element T,
SBS is used as the trigger element T2. In other words,
Since the breakover voltage of the SBS is lower, the SBS is designed to operate satisfactorily under a wide range of breakover voltages. According to this phase control circuit, even if there is a fluctuation in the input voltage of volts as shown in FIG. Based on the time constant determined by the switching element T, as shown in FIG. 3(b),
It is possible to control the firing angle of the ignition valve, and therefore, it is possible to suppress fluctuations in the load current to a small level. Furthermore, the element used as the conventional trigger element T2 is the trigger element T.

By reusing it as a phase control circuit, it becomes an inexpensive phase control circuit.

By the way, in the above explanation, Gui7 is used as the trigger element T.
We have explained the case where SBS is used as the trigger element T2 using the trigger element T2, but the breakover voltage of the diac is subdivided into several volts, and if a trigger element with a low breakover voltage is used as the trigger element T2, the trigger tf'#
, and child T21T3 can both be diacs.

In this case, an SBS with an unnecessary gate terminal like an SBS
This eliminates the need to use BS.

[Effect of the invention 1 As described above, the present invention connects the second bidirectional tri-gamma element in parallel to both ends of the series circuit of the variable resistor and the capacitor, so that the voltage of the AC power source fluctuates. Also, the voltage across the variable resistor and capacitor of the gate circuit can be maintained at a substantially constant voltage by the second bidirectional trigger element, and therefore the switching element can be stably operated without being affected by voltage fluctuations of the AC power supply. The firing angle can be easily controlled, and the fluctuations in the load current when the voltage of the AC power source fluctuates can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a voltage-current characteristic diagram of the trigger element as described above, FIG. 3 is an explanatory diagram of the operation as described above, and FIGS. 4(a) and (b) are respectively FIG. 5 is a circuit diagram showing a conventional phase control circuit, FIG. 5 is an explanatory diagram of the operation of the same, and FIG. 6 is an explanatory diagram of the problem of the same. T1 is a switching element, T2. T is a trigger element, A
C is an AC power supply, L is a load, C is a capacitor, ■R is a variable resistor, and 1 is a gate circuit. Agent Patent Attorney Ishi 1) When entering Figure 7, Figure 2, Figure 3, and inputting Figure 5,

Claims (2)

[Claims] (1) A bidirectional switching element connected in series to an AC power supply via a load, and a gate circuit that controls conduction of this bidirectional switching element every half cycle of the AC power supply, A capacitor that is charged and discharged every time, a variable resistor that adjusts the current supplied to this capacitor to control the firing angle of the bidirectional switching element, and when the voltage across the capacitor rises above the breakover voltage. a first bidirectional trigger element that discharges the charge in the capacitor and causes a gate current to flow through the bidirectional switching element; and a second bidirectional trigger element that is connected in parallel to both ends of the series circuit of the variable resistor and the capacitor. A phase control circuit comprising the above-mentioned gate circuit with a magnetic trigger element. (2) The phase control circuit according to claim 1, wherein the second bidirectional trigger element has a higher breakover voltage than the first bidirectional trigger element.