JPS623449B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a thyristor phase control device.

As is well known, thyristors are widely used as switches for power control, and there are various types of gate circuits that control conduction of these thyristors.

A conventional, common gate circuit is shown in FIG. Regarding this circuit, a transistor 11 is made conductive by a DC input voltage applied to an input terminal 10, and a unijunction transistor (hereinafter referred to as
A current is applied to a relaxation oscillation circuit formed by a UJT (abbreviated as UJT) 12 and a capacitor 13. UJT12
Obtain a pulse voltage and transfer it to the pulse transformer 14
Thyristors 15 and 16 connected in antiparallel through
is ignited.

In this circuit, there is no linear relationship between the change in the DC input voltage and the change in the thyristor-controlled load 18 voltage, making it unsuitable for precise adjustment. In order to improve this linearity, the load voltage controlled by the thyristor can be negatively fed back to the input of the amplifier to improve the linearity.

Figure 2 shows the principle, and the load resistance 2
A transformer 30 is provided at both ends of the 8, and a feedback voltage is obtained through a rectifier 31, a resistor 32, and a smoothing capacitor 33. Since the feedback voltage must be direct current, it is necessary to sufficiently eliminate pulsations with the resistor 32 and capacitor 33, which increases the time constant of the smoothing circuit. When the input voltage at the input terminal 20 increases, there is a delay in the feedback voltage due to the time constant, and the load 28
Since the voltage temporarily becomes overvoltage, there is a limit to the speed of input voltage change. Furthermore, as the amplification degree of the transistor 21 is increased, this tendency becomes even greater, so it is necessary to lower the amplification degree or to slow down the rate of change of the input voltage. When the degree of amplification is lowered, the accuracy of improving linearity deteriorates.

An object of the present invention is to provide a highly accurate thyristor phase control device that improves the linearity of input voltage versus output voltage and also improves response characteristics.

Embodiments of the present invention shown in the drawings will be described below.

FIG. 3 is a circuit diagram showing an embodiment of the device of the present invention. In FIG. 3, input terminal 40 is connected to a non-inverting input terminal of differential operational amplifier 41. In FIG. A DC input signal for control is applied to this input terminal 40, and the phase of the thyristor connected to the load is controlled according to the signal level.

Differential operational amplifier 41 connected to input terminal 40
As will be described later, the integrator constitutes an integrator together with the integrating capacitor 56, and generates at its output an integrated voltage proportional to the product of the input resistor 39 and the integrating capacitor. The output amplified by the differential operational amplifier 41 is applied to a UJT 45 for relaxation oscillation and a capacitor 44 via transistors 42 and 43 for current detection.

The pulses obtained by the UJT 45 are applied to the thyristors 46 and 47 via a pulse transformer 57, and the current from the AC power source 49 is applied to the thyristors 46 and 47.
47 and is applied to the load 48.

In the present invention, a feedback circuit is provided for negatively feeding back a signal having a waveform similar to the signal supplied to the load. In the embodiment, the feedback signal is obtained as follows. That is, a voltage obtained from an AC power source 49 is converted to a low voltage by a step-down transformer 50, double-wave rectified by rectifiers 51 and 52, and applied to a photocoupler 53 optically coupled to a light emitting diode and a light receiving thyristor. The thyristor of this coupler is ignited at the same timing as the thyristors 46 and 47 because the pulse voltage from the pulse transformer 57 is applied from the light emitting diode. Therefore, the waveform applied to load resistor 54 is the same as load 48. In other words, the load control signal is fed back from the load 48.

This feedback signal is applied through an integrating resistor 55 to an inverting input 58 of the differential operational amplifier 41. An integrating capacitor 56 is provided between the inverting input 58 and the output, and the differential operational amplifier 41, the integrating resistor 55, and the integrating capacitor 56 constitute an integrating circuit. Therefore, by appropriately selecting constants, the output voltage of the differential operational amplifier 41 will be free from pulsations. Also, since the DC input voltage applied to the non-inverting input terminal is negatively fed back from the output to the inverting input terminal via the integrating capacitor 56, no overvoltage is transiently applied to the load 48, so the gain of the amplifier 41 is made very large. You can take it.

Since the open loop amplification degree of the operational amplifier circuit is 100,000 times or more, there is a large amount of negative feedback, so the linearity with respect to changes in the input voltage at the input terminal 40 and the average value voltage of the load 48 is very good. . At the same time, even if the voltage of the AC power supply 49 changes, the input voltage of the amplifier and the feedback voltage are always fed back to be equal, and since the feedback voltage and the load voltage of the load 48 are in a proportional relationship, when the input voltage is constant, the The result is that the voltage 48 does not change, resulting in stability and high accuracy even with power supply voltage fluctuations.

The apparatus of the present invention has been described above with respect to one embodiment, but when the apparatus of the present invention is used in an electric furnace, for example,
Highly accurate and stable temperature control can be performed.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional thyristor phase control device, Fig. 2 is a circuit diagram showing an example of a conventional device improved from the device in Fig. 1, and Fig. 3 is a thyristor phase control device of the present invention. FIG. 2 is a circuit diagram showing one embodiment of the present invention. Explanation of symbols of main parts, 41, 55, 56...
Integral amplifier circuit, 44, 45...pulse generation circuit,
46, 47...Thyristor, 48...Load, 5
0, 51, 52, 53, 54...Feedback circuit.

Claims (1)

[Scope of Claims] 1. An integral amplifier circuit into which a DC control signal is input; a pulse generating circuit that generates pulses with different phases according to the output of the integral amplifier circuit; and conduction by the output pulse of the pulse generating circuit. A thyristor to be controlled, a load connected to an AC power supply via the thyristor, and a negative feedback circuit that negatively feeds back a signal having a waveform similar to the signal supplied to the load to the input of the integral amplifier circuit. A thyristor phase control device comprising: 2. In the device according to claim 1, the integral amplifier circuit is an integrator made of a differential amplifier, and applies a DC control signal to a non-inverting input terminal, and supplies the DC control signal to the load fed back through a negative feedback circuit. A thyristor phase control device characterized in that a signal having a waveform similar to that of a signal applied to an inverting input terminal is applied to an inverting input terminal. 3. In the device according to claim 1 or 2, the negative feedback circuit includes a primary coil and a secondary coil, and the primary coil is connected to an alternating current for supplying power to the load. A thyristor phase control device comprising a transformer that inputs the voltage generated by a power source, a rectifier that rectifies the signal generated in the secondary coil of the transformer, and a photocoupler that controls the phase of the rectified output of the rectifier. .