JPS6366032B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature detection device using electrical resistance, and more specifically, a heater is also used as a resistance temperature sensor, the heater temperature is measured immediately after the zero cross of the AC power supply, and the following measurement is performed according to the measurement result. The present invention relates to a device that controls on/off of heater drive during a half cycle period.

Generally, a commercial AC power source is used as the power source for driving the heater, so when the heater is also used as a temperature detection sensor, in order to prevent the AC voltage from being directly applied to the circuit that processes the output voltage of the sensor,
A blocking diode must be used. In this case, the forward voltage drop of the blocking diode is approximately
Although it is very small at 0.6V, this slight forward voltage drop of the diode becomes a problem if you are trying to improve measurement accuracy.

The purpose of the present invention is to reduce the number of component parts as much as possible, reduce the power loss consumed for temperature measurement as much as possible, and have very high temperature measurement accuracy, so that the heater temperature can be set easily. An object of the present invention is to provide a heater drive control device that can accurately control a value.

The heater drive control device of the present invention connects a series circuit of a heater and a triax, which also serves as a resistance temperature sensor, to an AC power supply terminal, and provides a DC power supply with the heater side of the AC power line as a common line. The emitter of the conducting switching transistor is connected to the non-common side line of the above DC power supply, and the collector of the transistor is connected through a resistor in the direction in which current flows through both of the two diodes when the transistor switches. The other side of one diode is connected to the connection point of the heater and the triax, and a load impedance is connected between the other diode and the common line, and the temperature is measured from the connection point of the load impedance and the diode. The present invention is characterized in that a detection signal is extracted and the above-mentioned triax is controlled on/off based on the magnitude relationship between the temperature detection signal value and a set value.

Next, embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a circuit diagram of an embodiment of the present invention.

A DC power supply circuit 4 connects a series circuit of a heater 1 and a triax 2, which also serve as sensors, to AC power supply terminals 3A and 3B, and converts this AC power into stabilized DC.
The positive electrode side of the DC power source is connected to the AC power terminal 3A on the heater side to form a common line 5, and the negative electrode side of the DC power source is a non-common line 6.

A zero-crossing detection circuit 7 is provided which is operated by a DC power supply and detects the zero-crossing of the AC power supply, and the emitter of a switching transistor 8 which is turned on by this zero-crossing detection signal is connected to the non-common line 6 of the DC power supply, and the emitter of the switching transistor 8 is connected to the non-common line 6 of the DC power supply.
The cathodes of two diodes 10 and 11 are commonly connected through a resistor 9 from the collector of the diode 10 to the connection point H between the heater 1 and the triac 2, and the anode of the other diode 11 is connected to the connection point H of the heater 1 and the triac 2. A load impedance 12 is connected between the load impedance 12 and the common line 5, and a temperature measurement signal em is taken out from a connection point F between the load impedance 12 and the diode 11. On the other hand, a diode 13 and resistors 14 and 15 are connected in series between the collector of the transistor 8 and the common line 5, and the control set voltage es is taken out from the contact point E. The comparator 16 determines the magnitude relationship of the measurement signal em with respect to the set voltage es. The output line G of the comparator 16 is connected via a diode 17 to the control gate of the triac 2. As is clear from this circuit configuration, the diodes 11 and 13
and resistors 9, 12, 14, and 15 form a first brittle circuit for comparing the measured value and the reference value, and heater 1, diodes 10, 11, and resistor 12 change the potential of terminal H of heater 1 to the measurement point. It forms a second bridge circuit for copying to F. Note that the value of the resistor 12 is selected to be sufficiently higher than the resistance value of the heater 1.

Next, the effect will be explained. FIG. 2 shows voltage waveforms at various parts in FIG. 1, where () indicates when the measured temperature is higher than the set temperature, and () indicates when the measured temperature is lower than the set temperature. Each waveform A to H corresponds to each point A to H in FIG.

The AC power supply waveform is a sine waveform as shown in Figure A, and when the potential at point A becomes the same potential as the common line, a zero cross signal is output as shown in Figure B. This zero-cross signal causes transistor 8 to become conductive for a moment, supplying measuring current to the first and second bridge circuits. Triack 2 is activated at any time due to the zero crossing of the AC power supply voltage.
is turned off.

A reference potential es is obtained from a connection point E on one side of the first bridge circuit. This reference potential es can be adjusted by a variable resistor 15.

Regarding the second bridge circuit, the forward voltage drop of the diode 10 due to the heater current i ₁ and the diode 11 due to the current i ₂ of the load impedance 12
If the design is made so that the forward voltage drop is equal to the forward voltage drop, the potential at point F becomes equal to the potential at point H. For example, if i ₁ = 10i ₂ , using diodes with the same characteristics, one diode 10 can be replaced by one diode 1.
This can be realized by configuring ten diodes 1 connected in parallel, or by configuring one large capacity diode 10 and a plurality of small capacity diodes 11 connected in parallel.

On one side of the first bridge circuit for detecting measured values, the current flowing through the resistor 9 is a combination of (i ₁ + i ₂ ), but if i ₁ ≫ i ₂ , the current flowing through the resistor 9 is due to a change in the resistance of the heater 1. , occupies most of it, and the change in resistance of the heater 1 almost becomes the change in point F.

A comparator 16 compares the measured value em thus obtained and the reference value es described above. When the measured temperature is higher than the reference temperature, no trigger pulse is applied to the triac, as shown in (), and the triac remains off for the next half cycle. Conversely, if the measured temperature becomes lower than the reference temperature, a trigger pulse is applied to the triac after the zero-crossing period, and the triac is turned on for the next half cycle.

When the triax 2 is on and the non-common line point A is higher than the common line in a positive half cycle a, an alternating current voltage appears at point D as shown in figure D, but the diode 11 prevents this alternating voltage from occurring. During the opposite negative half-cycle b, diode 10 blocks the alternating voltage. As a result, even when the heater 1 is energized, high AC voltage is not applied to the measurement value input terminal F point of the comparator 16 during non-measurement periods. Also,
During the positive half cycle, as shown in Figure C, an AC voltage also appears at point C, but the diode 13 blocks this AC voltage, so a high AC voltage is applied to the reference value input terminal of the comparator 16 at point E. It is never applied. Note that since the transistor 8 is selected to have a high collector breakdown voltage, it can withstand a positive half cycle.

FIG. 3 shows an embodiment of a display device according to the present invention that constantly displays the temperature of the measured value em measured at each zero cross. Circuit 2 consisting of operational amplifier _A1
1 is an impedance conversion circuit. operational amplifier
The circuit 22 consisting of A ₂ is an adder, and its output em ₂ is given as em ₂ =−(R ₂ /R ₁ em ₁ +R ₂ /R ₃ E _REF ) when the inputs are em ₁ and E _REF . Become. A circuit 23 consisting of an operational amplifier A ₃ is a circuit for obtaining a positive potential reference voltage E _REF from a DC voltage E ^- . A zero-crossing signal is applied to the gate electrode of the FET 24, and this transistor 24 becomes conductive at each zero-crossing. The sample and hold circuit 25 holds the output em ₂ of the adder and updates its value at every zero cross. The A/D converter 26 digitally converts the output voltage of the sample and hold circuit 25 using E _REF as a reference voltage. The display device 27 visually displays the value.

In the above equation regarding the adder 22, since the voltage em is a negative value, the part in the brackets of the above equation is a subtraction process, and when the heater temperature is 0°C, the output voltage is 0V.
The resistor R ₃ can be selected so that , and the resistor R ₁ can be selected so that an output voltage proportional to temperature can be obtained. In this way, the output at 0℃ is
0V, and a positive voltage em ₂ proportional to the temperature rise is obtained.
This can be displayed.

According to the present invention, there are the following effects.

Since it serves as both a resistance temperature sensor and a heater, only two lead wires are required for the sensor and heater, making it especially effective when the heater temperature is to be controlled, such as in hair irons, electric blankets, etc. .

Since the temperature detection current flowing to the heater is extremely short at zero cross, it is easy to flow a large pulsed current to it, and a large detection voltage can be obtained even when the heater resistance value is small. This eliminates the need for an amplifier circuit and simplifies the detection circuit configuration.

Since the AC voltage applied to the heater during non-temperature measurement is blocked by the diode, no trouble occurs to the control circuit such as the comparator.

The voltage drop caused by the two diodes 10 and 11 forming the second bridge circuit is canceled out, and a voltage that is equal to the voltage at the heater terminal point H appears at the measurement signal detection point F, improving the temperature measurement accuracy.

If the value of the load impedance 12 forming the second bridge circuit and the heater resistance value are selected to be sufficiently large, the voltage change due to the change in heater resistance during temperature measurement will almost always become the voltage change at the measurement signal detection point F. Temperature measurement sensitivity is improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is an operation explanatory diagram showing voltage waveforms at each part thereof, and FIG. 3 is a circuit diagram showing an embodiment of a display device related to the present invention. DESCRIPTION OF SYMBOLS 1... Heater that also serves as a sensor, 2... Triax, 3A, 3B... AC power supply terminal, 4... DC power supply circuit, 7... Zero cross detection circuit, 8... Switching transistor, 9... Resistor, 10, 1
1...Diode, 16...Comparator.

Claims (1)

[Scope of Claims] 1. A series circuit of a heater and a triax that also serves as a resistance temperature sensor is connected to an AC power supply terminal, and a DC power supply is provided with the heater side of the AC power line as a common line, and conduction occurs at the zero cross of the AC power supply. Connect the emitter of the switching transistor to the non-common line of the DC power supply, and
Connecting the collector of the transistor through a resistor in the direction in which current flows through both of the two diodes when the transistor switches, and connecting the other of the diodes to the connection point between the heater and the triax, Connect a load impedance between the other diode and the above common line, take out the temperature detection signal from the connection point between the load impedance and the diode, and perform the above triact based on the magnitude relationship between this temperature detection signal value and the set value. A heater drive control device characterized by being configured to perform on/off control. 2 A variable voltage dividing circuit is provided between the common line through a diode from the collector of the switching transistor, and a reference voltage for temperature detection is obtained from the voltage dividing point.
Heater drive control device as described in .