JPS63219013A - Temperature control circuit - Google Patents

Abstract

PURPOSE:To dispense with the detecting resistor of a load current, and besides, to make a heat generation smaller, and further, to eliminate the change of a temperature set value against the fluctuation of a power source by opening the resistance measuring part of a heater at the time when the heater is charged by electricity, and measuring under a low voltage only when it is necessitated. CONSTITUTION:An AC power source 1 is half-wave-rectified, and a capacitor 6 is charged by the Zener voltage of a voltage regulator diode 4. A control circuit 11 outputs periodically a signal to close a switch circuit 10, while the trigger pulse (PT) of a triode AC switch (TA) 2 is not outputted. When the circuit 10 is closed, a current flows in a resistor 8, and a voltage drop is obtained. When the temperature of the heater 3 is low, the resistance is also low, and the voltage of the resistor 8 is larger than a reference voltage 9. The circuit 11 controls the output/stop of the trigger signal and the close/open of the circuit 10 while storing these data. The TA 2 heats the heater 3 during the output of the pulse PT. Accordingly, because the voltage of the resistor 8 goes down lower, if the resistance value is set so that it comes just to be temperature set value when the voltage of the resistor 4 comes lower than the voltage 9, the TA 2 continues an OFF state during an interval until the circuit 10 is closed next time after the circuit 10 is closed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a temperature control circuit, and in particular to an AC commercial power supply (
The present invention relates to a temperature control circuit that eliminates the need for a temperature sensor by using a heater whose resistance changes depending on the temperature in electrothermal control that obtains a high temperature by heating all of the heaters with A (referred to as z source).

Prior Art Conventionally, the temperature control circuit of this type has been constructed as shown in FIG. In FIG. 3, at 2, l is an AC power source, C is a trybook, and 3 is a heater, whose resistance value increases as the temperature rises.

13 is a resistor, /II is a reference power supply, /S is an OR gate, /
6 is a comparator, / is a tri-aracco gate trigger circuit (hereinafter referred to as a trigger circuit), and l is a periodic pulse generating circuit.

Next, the operation of the circuit shown in Fig. 3 will be explained.
Assume that the heater 3 is currently energized with the triator in the 1-on state.At this time, the resistance of the heater 3, the peak value of the voltage drop of the resistor 13 connected in series, and the reference power supply/4
Adjust so that when the values of ' are equal, the set value of @ degree is achieved. Immediately after energization, the resistance of the heater 3 is lower than when the temperature is set, so the voltage drop across the resistor 13 is higher than when the temperature is stable.
Since the comparator 16 detects and amplifies the value larger than the reference power supply /II and drives the trigger circuit 17, the gate signal is continuously applied to the triac λ and it continues to be 1" on. The temperature of the heater 3 rises. As the resistance increases, the voltage drop across the resistor /3 becomes smaller than the value of the reference power supply /l (the temperature reaches the set value).Therefore, the comparator /6
stops the driving of the trigger circuit/7, so the tri-aracco is turned off. When Triarakuco gets 1 off,
The resistance of the circuit including the heater 3 becomes extremely large.
In terms of temperature, this is equivalent to an extremely high temperature state, so one circuit remains stable as it is. The periodic pulse generation circuit/l triggers the triac for l cycles at a cycle sufficiently shorter than the thermal time constant of the heater J, so that when the resistance of the heater 3 is small (when the temperature does not reach the set value), then triggers the trial arco by the detection signal of comparator/6. By repeating this process, the temperature of the heater 3 is controlled to approximately the set value.

Problems to be Solved by the Invention By the way, the resistor 13 of the circuit 2 in FIG. 3 needs to be sufficiently small in terms of power loss.
In the case of a heater current of , the voltage drop o even at o, orΩ
, sV power consumption! Because of the increase in W and heat generation, the application of temperature control circuits using this method has been limited to control below /A at most.

Furthermore, the circuit shown in FIG. 3 has the disadvantage that the set temperature fluctuates due to fluctuations in the ACl source.

The present invention has been made in view of the above-mentioned conventional situation,
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a novel temperature control circuit which makes it possible to eliminate the above-mentioned disadvantages inherent in the conventional technology.

Means for Solving the Problems In order to achieve the above object, the temperature control circuit according to the present invention includes a triac connected in series with a load heater to an AC power source, and a triac that rectifies the AC power source to provide a predetermined DC power source. 0, a resistor connected in series with the load heater and connected to the DC power supply via a switch circuit that closes when the trybook is off, and a voltage drop across this resistor is compared with a reference voltage. and a trigger circuit that triggers the triac for a predetermined period when the voltage drop across the resistor is large.

Originality of the Invention In contrast to the conventional temperature control circuit described above, the present invention does not require a resistor to detect the load current, so there is no loss or heat generation in that part, and the temperature control circuit does not respond to fluctuations in the AC power supply. It has an original content in that the setting value does not change.

EXAMPLES Below, preferred embodiments of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

In Figure 1, reference number l is an AC power supply, ko is a triac, 3 is a heater, da is a constant voltage diode, 5 is a rectifier diode, 6 is a capacitor, ? , ff are resistors, 9 is a reference voltage, IO is a switch circuit, and // is a control circuit, which is composed of a comparison section, a memory section, a control signal output section, and the like.

Next, to explain the operation of the circuit shown in FIG.
The 9-source lt-rectifier diode performs half-wave rectification through the resistor 7, and the capacitor 6 is charged to the Zener voltage of the constant voltage diode. Here, the control circuit l/ periodically outputs a signal that closes the switch circuit IO when it is not outputting the trigger pulse of the tri-arco. switch circuit lO
When closed, capacitor 6, heater 3. Current flows through the closed circuit of resistor t, and a voltage drop is obtained across resistor t. At this time, when the temperature of the resistor 3 is low, the resistance is also small, and the voltage drop across the resistor is greater than the reference voltage 9. The control circuit // memorizes this comparison result, outputs a trigger signal for the trial raccoon for a predetermined period, then stops the trigger signal, and then
A signal for closing the switch circuit 10 is output. Triaraco is turned on during the output of the trigger pulse from the control circuit // and heats the heater 3, so its resistance value increases little by little. Therefore, the next time the switch circuit IO is closed, the voltage drop across the resistor t will be By repeating this process and setting the resistance t or the reference voltage so that the temperature setting value is reached when the voltage drop across the resistance t becomes lower than the reference voltage, the switch circuit 10 After closing, the trial arco is in the "off" state tt until the next time the switch circuit 10 is closed.Also, when the switch circuit 10 is closed next, the heater 3 cools down and its resistance becomes smaller, causing a voltage drop across the resistance t. When becomes large, the tri-arakuco is triggered again and the heater 3 is heated up, otherwise the tri-arakuco's 1 OFF'' continues until the next time the switch circuit io is closed.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention. Referring to FIG. 2, parts having the same functions in FIG. 2 as in FIG. 1 are designated by the same reference numerals.

As for other functions, 7.2 is an AC power supply zero point detection circuit (hereinafter referred to as zero point detection circuit). In this second embodiment, the closing signal for the switch circuit io is obtained from the zero point detection circuit 12. Therefore, the resistance of the heater 3 can be measured in a state where the load current is zero, regardless of the 1-ON state or 1-OFF state of the TRIARACCO.
Compared to the first embodiment described as FM, this embodiment has the advantage of allowing finer control.

In other words, although generally not required for temperature control, the control circuit/
It is also possible to use / as a phase control circuit.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, one of the triacs
Temperature control is performed by repeating "on" and "1 off", but when the heater is energized, the resistance measurement part of the heater is open and measurements are made at a low voltage only when necessary, so power consumption and heat generation are small, and AC Even if the power supply fluctuates, the power supply for resistance measurement is stabilized, resulting in less influence on temperature control.

[Brief explanation of drawings]

@I Figure is a circuit diagram showing a first embodiment of the present invention. FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. 3 is a circuit diagram showing an example of the configuration of a conventional circuit of this type. l...AC'1lfi, co...triac, 3.
...heater, da...regulating diode, j...rectifier diode, 6...capacitor, ? , ff...
Resistor, 9... Reference power supply, lO... Switch circuit, /
/...control circuit, /2...zero point detection circuit, 13...
・Resistance, /4'... Reference power supply, 15... OR gate, 16... Comparator, /7... Trigger circuit, 7g.
...Representative of periodic pulse generation circuit Patent attorney Hh Yutabe Tani +4! *Power supply diagram 3

Claims (1)

[Claims] A heater load whose resistance value changes depending on temperature is connected in series with a first switching means to an AC power source, means for rectifying the AC power source to obtain a predetermined DC power source, and the DC power source, the heater load, and the resistor. a closed circuit including a second switching means; a control means for closing the first switching means for a predetermined period based on a comparison result between the voltage drop of the resistor and a reference voltage; and means for closing for a predetermined period when the heater load current is opened or when the heater load current is smaller than a predetermined value.