JPS6319844Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a temperature control circuit that stabilizes temperature control.

FIG. 1 is a circuit diagram showing an example of a conventional temperature control circuit. In the figure, 1 is an AC power supply, 2 is a main thyristor (hereinafter referred to as thyristor) whose anode is connected to one end of the AC power supply 1, 3 is one end connected to the other end of the AC power supply 1, Heaters 4, 5a, and 5b as loads whose other ends are connected to the cathode of the thyristor 2 are connected in series, and both ends of the series body are connected to the thyristor 2.
A capacitor connected to the anode and gate of the thyristor 2 to trigger the thyristor 2 at zero voltage, respectively.
a first dividing resistor and a second dividing resistor, 6 a resistor connected between the gate and cathode of the thyristor 2;
7 is a rectifier diode for gate protection connected between the gate and cathode of the thyristor 2, and 8 is an anode of the thyristor 2 connected between the first dividing resistor 5a and the second dividing resistor 5.
b, its cathode is connected to the cathode of the thyristor 2, and the P gate is thermally coupled to the heater 3 or thermally coupled to the detected object that is thermally coupled to the heater 3. A heat-sensitive thyristor, 9 is a capacitor for gate noise prevention connected between the gate and cathode of the heat-sensitive thyristor 8, and 10 is a variable resistor connected in parallel with the capacitor 9 for setting the switch temperature of the heat-sensitive thyristor 8.

Next, the operation of the temperature control circuit according to the above configuration will be explained.

First, when the temperature of the object to be detected (not shown) is low, the heat-sensitive thyristor 8, which is switched on at a predetermined temperature, is in an off state. On the other hand, a capacitor 4 and a first and second dividing resistor 5 are connected to the gate of the thyristor 2.
Since a current leading in phase from the power supply voltage is supplied through a and 5b, the thyristor 2 is triggered and turned on when the power supply voltage is approximately zero. For this reason,
Heater 3 is supplied with power for a complete half cycle. When current flows through the heater 3, the temperature of the object to be detected (not shown) rises, and the heat-sensitive thyristor 8 is turned on. Therefore, the gate and cathode of the thyristor 2 are short-circuited. Therefore, the current that has been flowing to the gate of the thyristor 2 is bypassed to the heat-sensitive thyristor 8, so the thyristor 2 is turned off. Therefore, no current flows through the heater 3, and the temperature of the object to be detected naturally decreases, and by repeating the above-described operation, the temperature of the object to be detected can be controlled to be constant.

However, in the conventional temperature control circuit, as shown in FIG. 2, the characteristics of the heat-sensitive thyristor 8 are closely related to the switch temperature and the voltage between the anode and cathode (switch voltage). For this reason,
Even if the resistance value of the variable resistor 10 is constant, errors in the switch temperature may occur due to variations in the capacitance of the capacitor, variations in the resistance value of the dividing resistor, fluctuations in the power supply voltage, or fluctuations in the frequency of the power supply voltage. This will appear as , and the initially set temperature will fluctuate. That is, for example, if the switch voltage is
If the temperature rises from V _SW1 to V _SW2 , the switch temperature will be T _SW1
The switch voltage decreases from V _SW3 to T _SW2 .
There were drawbacks such as the switch temperature rising to TSW3 if the temperature dropped to T _SW3 .

In view of the above points, the present invention was developed to eliminate such drawbacks.The purpose of this invention is to eliminate variations in capacitance of capacitors, variations in resistance value of dividing resistors, fluctuations in power supply voltage, or fluctuations in power supply frequency. It is an object of the present invention to provide a temperature control circuit that eliminates fluctuations in set temperature caused by factors such as the above and stabilizes temperature control.

In order to achieve this purpose, the present invention connects a constant voltage diode between the anode and cathode of a heat-sensitive thyristor to stabilize the fluctuations in the switch temperature due to the voltage dependence of the switch temperature of the heat-sensitive thyristor. This will be explained in detail below using examples.

FIG. 3 is a circuit diagram showing an embodiment of the temperature control circuit according to the present invention. In FIG. 3, the same reference numerals as in FIG. 1 indicate corresponding parts, and 11 is a constant voltage diode connected between the anode and cathode of the heat-sensitive thyristor 8. In FIG.

Next, the operation of the temperature control circuit according to the above configuration will be explained.

First, the temperature control operation is the same as that shown in FIG. Anode of heat sensitive thyristor 8 in zero phase
The cathode-to-cathode voltage (switch voltage) is clipped to a constant value, and the switch temperature of the heat-sensitive thyristor 8 is always kept at a constant value.

FIG. 4 is a circuit diagram showing another embodiment of the temperature control circuit according to the present invention, in which an n-gate one is used as the heat-sensitive thyristor 8. In FIG. 4, the same parts as in FIG. 3 are given the same reference numerals, and their explanation will be omitted. In this case, the variable resistor 10 for setting the switch temperature and the capacitor 9 for preventing gate noise must be connected between the gate of the heat-sensitive thyristor 8 and the anode.

Note that the operation is, of course, the same as that in FIG. 3.

As explained in detail above, the temperature control circuit according to the present invention can be used to prevent variations in the capacitance or resistance value of the capacitor connected between the gate and anode of the thyristor, fluctuations in the power supply voltage, or fluctuations in the power supply frequency. This has the effect of keeping the controlled temperature constant even if there are fluctuations in temperature. Furthermore, since the main thyristor is turned on at zero volts, it is extremely effective in that no radio noise is generated and fluctuations in switch temperature can be stabilized.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional temperature control circuit, Fig. 2 is a diagram showing switch temperature versus switch voltage characteristics of the heat-sensitive thyristor shown in Fig. 1, and Fig. 3 is an example of a temperature control circuit according to the present invention. A circuit diagram showing an example,
FIG. 4 is a circuit diagram showing another embodiment of the temperature control circuit according to the present invention. DESCRIPTION OF SYMBOLS 1... AC power supply, 2... Thyristor, 3... Heater, 4... Capacitor, 5a and 5b... First dividing resistor and second dividing resistor, 6... Resistor, 7
... Rectifier diode, 8 ... Heat-sensitive thyristor, 9
... Capacitor, 10 ... Variable resistor, 11 ... Constant voltage diode. Note that the same numbers indicate the same or equivalent parts.

Claims (1)

[Scope of utility model registration request] A main thyristor connected in series with a load to an AC power source to control the energization state of the load; a capacitor connected between the anode and gate of the main thyristor to trigger the thyristor when the AC power source is at zero voltage; and a series body consisting of a plurality of divided resistors, a resistor connected between the cathode and the gate of the main thyristor, a resistor connected between the connection point of the plurality of divided resistors of the series body and the cathode of the main thyristor, A parallel body consisting of a heat-sensitive thyristor that senses the temperature of the load and becomes conductive when the sensed temperature exceeds a predetermined temperature, a capacitor for gate noise prevention connected to the gate of the heat-sensitive thyristor, and a variable resistor for setting the switch temperature; A temperature control circuit comprising a constant voltage diode connected between the anode and cathode of the heat-sensitive thyristor.