JPS59190715A - Alternating current switch circuit - Google Patents

Abstract

PURPOSE:To perform on-off control over a small or inductive load at a voltage zero-cross point stably in safety by using an oscillator which oscillates continuously in a half period after the voltage zero-cross point as a voltage zero-cross pulse generator. CONSTITUTION:When the temperature of a controlled system is lower than a set value, the temperature is detected by a detector 18 and sent to a control circuit 19. The circuit 19 opens a control terminal 2 for oscillation output after the next voltage zero-cross point by the signal. Consequently, the pulse oscillator 20 starts oscillating at the voltage zero-cross point and its oscillation output is sent to an electronic switch 16. The electronic switch 16 turns on securely almost at the voltage zero-cross point by a continuous pulse string which is sent subsequently even when a heater 17 is a small or inductive load and can not secure a hold current in the 1st pulse arrival. When the temperature of the controlled system is higher than the set value, on the other hand, the electronic switch 16 holds itself in the on state during the period because of its properties as a holding element and turns off at the next voltage zero-cross point.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC switch circuit, and particularly to an AC switch circuit for power control that is required to be completely and stably controlled without generating switching noise during on/off. .

In power control devices that are controlled on and off at relatively long intervals, such as heaters used for temperature control in AC circuits, it is required to control on and off at the voltage zero cross point in order to suppress noise to other devices as much as possible. be done.

Conventionally, a method is well known in which a voltage zero-crossing point is detected, a single zero-crossing pulse is generated, and an electronic switch such as a thyristor is controlled on/off at the voltage zero-crossing point depending on the presence or absence of this pulse. However, although this method is effective when the load is large and a current greater than the holding current of a thyristor or the like can be obtained within one zero-crossing pulse, it has a secondary drawback. In other words, for light loads or inductive loads, even if the electronic switch can only be turned on when a zero cross or a pulse occurs.

During the zero-cross pulse, no current greater than the holding current flows, and the zero-cross pulse disappears and the electronic switch turns off, making it impossible to expect perfect operation. A well-known countermeasure to this problem is to add a dummy resistor in parallel with the load, but it has various problems due to thermal limitations. Furthermore, a circuit that widens the width of the zero cross A pulse until a current greater than the holding current of the electronic switch flows and the electronic switch can be maintained in the ON state, or a circuit that delays the phase of the voltage zero cross point detection circuit with a capacitor or the like in advance to create a narrow zero cross 7 A circuit is being considered in which a voltage point at which a current greater than the holding current of the electronic switch can flow even with the cross width is used as a pseudo voltage zero-crossing point. However, the former method requires a zero-crossing pulse width adjustment circuit, and the latter method requires a zero-crossing point position adjustment circuit, making the circuit configuration complex. Furthermore, these readjustments may be difficult depending on the power supply frequency and the nature of the load. There are drawbacks such as the need for

The present invention aims to improve these drawbacks by making the voltage zero clock pulse generator an oscillator that continuously oscillates for half a cycle after the voltage zero cross point, without adding any new circuit.

Our aim is to provide a complete power control switch circuit that does not require readjustment depending on the nature of the load, and can perform complete and stable on/off control at the voltage zero cross point, especially for light loads or inductive loads. ing.

The present invention will be explained in detail below.

FIG. 1 shows an embodiment of an oscillator that detects a voltage zero-crossing point and oscillates continuously for half a cycle after that detection point.

1 is an AC input terminal, 2 is an oscillation output control terminal, and 3 is an oscillation output terminal. The manually applied alternating current is passed through a current limiting resistor 4, full-wave rectified by a diode blitz 5, and then clipped by a Zener diode 7. Here, a DC voltage is applied to the anode side of the N-type iris resistor 9 used as a single oscillation element, and a pulsating current voltage of the same frequency as the input power source is applied to the remote side by a diode 6 and a capacitor 8. . Cyrisk 9 turns on momentarily when the potential of its anode becomes higher than the potential of dirt. However, because the current when turned on is suppressed to a sufficiently low level by the anode side resistor 12, the on state is not maintained.
When the anode side capacitor 13 is discharged, it is turned off. Therefore, the oscillation frequency of the thyristor 9 is determined by the resistor 12 connected to the anode side of the thyristor 9. capacitor 13
and the resistor 10.11 connected to the gate side. Resistor] 4 is a resistor for discharging the capacitor 13.

Here, by selecting the clipping voltage of the Zener diode 7 sufficiently low with respect to the AC input voltage, the oscillation start point of the thyristor 9 can be set close to the voltage zero-crossing point of the AC input.

Furthermore, by selecting the oscillation frequency of the thyristor 9 to be sufficiently higher than the power supply frequency, even if the electronic switch cannot be kept in the on state by the j-th pulse.

This will be maintained in the second and subsequent .xi. pulses, and it is possible to suppress switching noise when turned on.

The oscillation output control terminal 2 is controlled by a control circuit (not shown) in either short-circuit or open mode. When the temperature of the controlled object is low, the control terminal 2 remains open and the Zyristor 9 oscillates normally.

On the other hand, when the temperature is high, the control terminal 2 is short-circuited and the operation of the shear thyristor 9 is stopped. To control on/off of electronic switches at voltage zero cross point.

A holding element is used in the above control circuit, and the control mode of the control terminal 2 changes instantaneously when the control mode changes from open to short circuit, and changes at the next voltage zero cross point when the control mode changes from short circuit to open. .

FIG. 2 is a configuration diagram of a temperature control circuit to which the present invention is applied. 15 is an AC power supply, 16 is an electronic switch such as Cyrisk, 17 is a heater, 18 is a temperature detector that detects the temperature of the object to be controlled, and 19 is a signal from the temperature detector 18, as explained in FIG. - Chill with the control circuit that controls the gurus oscillator 20.

When the temperature of the controlled object is lower than the set value, the salinity is detected by the detector 18 and sent to the control circuit 19. The control circuit 19 uses the signal to open the control terminal 2 shown in FIG. 1 after the next voltage zero cross point. Therefore, the pulse oscillator 20 starts oscillating at the voltage zero crossing point, and its oscillation output is sent to the electronic switch 16. In the electronic switch 16, even if the heater 17 is under a light load or an inductive load and the current cannot maintain the holding current when the first pulse arrives, the continuously sent pulse train will ensure that the heater 17 is turned on near the stain pressure zero cross point. Become.

When AC power is applied to the heater 17 in this manner, the temperature of the controlled object increases.

On the other hand, if the temperature of the controlled object is higher than the set value, the control terminal 2 in FIG. 1 is immediately short-circuited by a signal detected by the temperature detector 18 and sent to the control circuit 19. Therefore, the output of oscillator 20 is turned off at that point. However, because the electronic switch 16 is a holding element, it remains on during the period and turns off at the primary voltage zero cross point, so the temperature of the controlled object gradually decreases. In this way, since the on/off control of the electronic switch 1G is performed at or near the voltage zero crossing point, switching noise to external equipment can be suppressed to a low level.

In the embodiment, an N-type IRIS was used as the 6-pulse oscillator, but it goes without saying that the present invention is not limited to this and that other active elements can be used.

As described above, according to the present invention, the voltage zero cross detection circuit that generates the 5.7 pulses is made into an oscillation circuit that continuously oscillates for half a period from the voltage zero cross point, without adding any new circuit.

Moreover, even in the case of a light load or an inductive load, it is possible to completely and stably perform power control that performs on/off control at the voltage zero cross point without readjusting in response to fluctuations in the power supply frequency.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a voltage zero-cross point and pulse oscillator according to the present invention, and FIG. 2 is a block diagram showing an application example of the present invention. 1. AC input terminal, 2.. Oscillation output control terminal. 3... Oscillation output terminal, 4... Current limiting resistor, 5...
Full-wave rectifier diode glitch, 7 ・Zener diode, 9...Sirisk, 1'0.11...key-
12... Resistor for adjusting anode potential. 13. Anode potential adjustment capacitor, 14. Capacitor discharge resistor, 15 AC power source, 16. Electronic switch, 17. Heater, 18. Temperature detector. 19... Control circuit, 20... Pulse oscillator. Figure 1 Figure 2

Claims (1)

[Claims] 1) In an AC circuit, an oscillator that detects a voltage zero-crossing point and oscillates continuously for half a cycle after that detection point, an electronic switch that is controlled on/off by the output of the oscillator, and a state of the controlled object (e.g. It consists of a state detector (e.g. temperature detector) that detects the temperature) and a control circuit that controls the operation of the oscillator according to the detection signal of the detector. An AC switch circuit for power control that is characterized by on/off control at voltage zero-crossing points.