JPH0248886Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to a heating element control device for an electric carpet or the like using a heating element formed of a positive temperature coefficient thermistor, for example.

[Technical background of the invention and its problems]

Generally, as a heating element made of a positive temperature coefficient thermistor generates heat, its internal resistance increases, thereby restricting the flow of current, thereby controlling its own temperature rise. However, in such a device, when electricity is started when the heating element is cold, a large current flows immediately after the heating element starts being energized because its own internal resistance is considerably low. Such heating elements are used, for example, in electric carpets, etc., and because of the large amount of heat generated and the heating area of such heating elements, there was a problem that a considerable amount of current flows immediately after the power is turned on. Conventional appliances using this type of heating element do not take measures against large currents, so they have the disadvantage that household circuit breakers are tripped by the large currents that flow at the beginning of use.

[Purpose of invention]

The purpose of this invention was to eliminate the above-mentioned drawbacks, and is to provide a heating element control device in which there is no risk of a large current continuing to flow even if electricity is started in a state where the internal resistance of the heating element is low. .

[Summary of the idea]

This device uses a first gate trigger circuit to control a closed-circuit controlled rectifying element consisting of an AC power source, a three-terminal controlled rectifying element, and a heating element formed by a positive temperature coefficient thermistor, with a relatively small predetermined conduction in synchronization with the power supply cycle. The first and second gate trigger circuits are alternately outputted from the oscillation circuit. a first pulse signal whose pulse width is at least longer than the power cycle; and a second pulse signal whose pulse width is even longer than the first pulse signal.
On the other hand, when a current exceeding the set level flows through the closed circuit, a monostable multivibrator is operated at the timing when the first pulse signal is output, and oscillation is caused by the vibrator output. The output of the second pulse signal from the circuit is stopped and the first pulse signal is converted into a third pulse signal having a sufficiently long pulse width.

[Example of idea]

Examples of this invention will be described below with reference to the drawings.

As shown in FIG. 1, a heating element 3 formed of a positive temperature coefficient thermistor is connected to a first AC power source 1 via a bidirectional three-terminal control rectifying element 2 to form a closed circuit. A current transformer 4 is provided in the closed circuit as a current detector in a non-contact manner. Also unstable multivibrator AM, this vibrator
An oscillation circuit OSC is provided, which includes a first two-input NAND gate 5 that inputs the AM output to one input terminal, and an inverter 6 that inverts the output of the NAND gate 5. The above-mentioned unstable multivibrator AM is well-known, and includes inverters I ₁ , I ₂ , and I ₃ connected in series, and the series circuit includes a resistor R ₁ and a diode D ₁ , and a resistor R ₂ and the diode D. It is formed by connecting in parallel a parallel circuit with a series circuit of a diode D ₂ having a polarity opposite to that of _{1, and connecting a capacitor C in parallel to the series circuit of the inverters I 1 and} I ₂ . The unstable multivibrator AM is the second
As shown in a of the figure, a rectangular wave signal is output that is at a low level for a period _T1 , which is at least slightly longer than the power supply cycle, and is at a high level for a period _T2 , which is longer than the period _T1 . The oscillation circuit OSC outputs a first pulse signal with a pulse width of _T1 from the NAND gate 5 while a high level signal is supplied to the other input terminal of the NAND gate 5, and the inverter 6 outputs a first pulse signal with a pulse width of T1. A second pulse signal of _T2 is output. The oscillation circuit OSC supplies a first pulse signal to a first gate trigger circuit GT ₁ and a second pulse signal to a second gate trigger circuit GT ₂ .
The input terminal of a full-wave rectifier diode bridge 8 is connected to an AC power source 7 obtained by stepping down the voltage of the power source 1 through a transformer (not shown), and the output terminal of the diode bridge 8 is connected to an AC power source 7 through a resistor 9. A constant voltage diode 10 is connected. The negative terminal side of the output terminal of the diode bridge 8 is grounded.
The first and second gate trigger circuits GT ₁ and GT ₂ are connected between both ends of the constant voltage diode 10, respectively. the first gate trigger circuit
GT ₁ consists of a series voltage divider circuit consisting of resistors 11 and 12 and a first transistor 13 of NPN type, and a second transistor of PNP type.
transistor 14, resistor 15 and capacitor 1
A series time constant circuit of 6 and a series voltage dividing circuit of resistors 17 and 18 are connected in parallel with each other, and the base of the second transistor 14 is connected to the connection point of the resistors 11 and 12. A primary winding of a pulse transformer 20 is connected between both ends of the capacitor 16 via the anode and cathode of a PUT element 19.
The gate of the PUT element 19 is connected to the resistor 17,1.
8, and the secondary winding of the pulse transformer 20 is connected between the gate and terminal of the control rectifying element 2. the second gate trigger circuit
GT ₂ connects in parallel a series voltage divider circuit of resistors 21 and 22 and a third NPN transistor 23, and a series time constant circuit of a fourth PNP transistor 24, a variable resistor 25, and the capacitor 16, The base of the fourth transistor 24 is connected to the resistor 2.
It is connected to connection points 1 and 22. Said resistance 1
The series voltage dividing circuits 7 and 18, the PUT element 19, and the pulse transformer 20 are used in common with the first gate trigger circuit _GT1 . and the oscillation circuit OSC
The output terminal of the NAND gate 5 is connected to the base of the first transistor 13 via a resistor 26,
The output terminal of the inverter 6 is connected to the base of the third transistor 23 via a resistor 27.

The current transformer 4 is connected to the input end of the comparator circuit COM. The comparison circuit COM+E
A reverse polarity series circuit of diodes 28 and 29 and a series voltage divider circuit of resistors 30 and 31 are connected between the terminal and ground, and the connection point of the diodes 28 and 29 is connected to the non-inverting input terminal (+) of the comparator 32. At the same time, the connection point between the resistors 30 and 31 is connected to the inverting input terminal (-) of the comparator 32. The current transformer 4 is connected in parallel to the diode 29 via a resistor 33. The output terminal of the comparison circuit COM, that is, the output terminal of the comparator 32, is connected to a two-input NAND gate 3.
It is connected to one input end of 4. The oscillation circuit OSC is connected to the other input terminal of the NAND gate 34.
The output terminal of the NAND gate 5 is connected.
The output terminal of the NAND gate 34 is connected to the input terminal of a monostable multivibrator MM. The monostable multivibrator MM is well known and includes a pair of two-input NAND gates 35 and 36, and the output terminal of the NAND gate 35 is connected to one input terminal of the NAND gate 36 via a capacitor 37. grounded via a resistor 38, connected to one input terminal of the NAND gate 36 and further grounded via the resistor 38, connected to one input terminal of the NAND gate 36 and further grounded via the resistor 38;
The output terminal of the NAND gate 36 is connected to one input terminal of the NAND gate 35. The output terminal of the NAND gate 34 is connected to the other input terminal of the NAND gate 35, and the other input terminal of the NAND gate 36 is connected to the +E terminal. The output terminal of the monostable multivibrator MM, that is, the output terminal of the NAND gate 36, is connected to the other input terminal of the NAND gate 5 of the oscillation circuit OSC.

In the embodiment of the present invention constructed in this manner, when a signal is received at the base terminal of the first transistor 13, the first transistor 13 becomes conductive, and as a result, the base current of the second transistor 14 flows. The second transistor 14 becomes conductive. Therefore, the capacitor 16 is charged by the time constant determined by the resistor 15 and the capacitor 16, and when this charging voltage exceeds a certain level value determined by the voltage division of the resistors 17 and 18.
The PUT element 19 becomes conductive, a pulse current flows through the primary side of the pulse transformer 20, a pulse is generated on the secondary side, and the control rectifier element 2 is controlled to be conductive. Here, to specifically explain the action of the capacitor 16 when discharging, the capacitor 16
6 is charged, and when this charging voltage exceeds a certain level determined by the voltage division of resistors 17 and 18,
The PUT element 19 becomes conductive, and the charge stored in the capacitor 16 is discharged accordingly. However,
1 of the pulse transformer 20 through the PUT element 19
A pulse current flows to the next side and a pulse is generated on the secondary side. This pulse is supplied to the gate of the controlled rectifying element 2, and the controlled rectifying element 2 is in a conductive state for a period from the input of the pulse to the next zero-crossing point of the AC power source 1. At this time, the capacitor 1
6 is charged, while each resistor 17, 18
The voltage determined by the partial voltage is full-wave rectified by the full-wave rectifying diode bridge 8, and the voltage formed by the constant voltage diode 10 drops as it approaches the zero-crossing point. The connection point of each of the resistors 17 and 18 is connected to the gate of the PUT element 19,
Therefore, the gate voltage of the PUT element 19 also decreases,
Within the _T1 period, the charging voltage of the capacitor 16 increases further.
The gate voltage of the PUT element 19 becomes higher than that, and the PUT element 19 becomes conductive, and at the same time, all the charges in the capacitor 16 are discharged. However, since the controlled rectifying element 2 is in a conductive state from the input of the pulse to the next zero-crossing point of the AC power source 1 as described above, the pulse is inputted to the controlled rectifying element 2 again and there is no effect. At this time, the conduction angle of the controlled rectifying element 2 is set to a relatively small predetermined conduction angle, for example, 90 degrees. Further, when a signal is received at the base terminal of the third transistor 23, the third transistor 23
becomes conductive, and as a result, the base current of the fourth transistor 24 flows and the fourth transistor 24 becomes conductive. Therefore, variable resistor 25 and capacitor 16
The capacitor 1 is determined by the time constant determined by
6 is charged and this charging voltage exceeds a certain level value determined by the voltage division of resistors 17 and 18, PUT
The element 19 becomes conductive, a pulse is generated on the secondary side of the pulse transformer 20, and the control rectifying element 2 is controlled to be conductive. Here, the action of the capacitor 16 when discharging will be explained in detail again. The capacitor 16 is charged according to a time constant determined by the resistor 25 and the capacitor 16, and this charging voltage is applied to the resistor 17 and the capacitor 16.
When the voltage reaches a certain level determined by the partial voltage of 18, the PUT element 19 becomes conductive, and the charge stored in the capacitor 16 is discharged. Similarly to the above, a pulse current flows through the PUT element 19 to the primary side of the pulse transformer 20, and the second
A pulse is generated on the next side. This pulse is supplied to the gate of the controlled rectifying element 2, and this pulse is supplied to the gate of the controlled rectifying element 2.
is in a conductive state for a period from when a pulse is input to the next zero cross point of the AC power supply 1. At this time, the capacitor 16 is charged, but on the other hand, the voltage determined by the voltage division of each resistor 17 and 18 is full-wave rectified by the full-wave rectifier diode bridge 8, and the voltage formed by the voltage regulator diode 10 is It descends as it approaches the zero-crossing point. Each of these resistors 1
The connection point between 7 and 18 is connected to the gate of the PUT element 19, and therefore the gate voltage of the PUT element 19 also decreases, and the capacitor 1 is connected again within the _T2 period.
6 becomes higher than the gate voltage of the PUT element 19, the PUT element 19 becomes conductive, and at the same time, all the charges in the capacitor 16 are discharged. However, since the controlled rectifying element 2 is in a conductive state from the time the pulse is input to the next zero-crossing point of the AC power source 1 as described above, there is no effect even if the pulse is input to the controlled rectifying element 2 again. . The conduction angle of the control rectifying element 2 at this time is arbitrarily set by changing the resistance value of the variable resistor 25.

On the other hand, in the oscillation circuit OSC, the astable multivibrator AM outputs the rectangular wave signal shown in a of FIG. The NAND gate 5 outputs a first pulse signal with a time width of T ₁ as shown by the circle in b in Figure 2, and the inverter 6 outputs a first pulse signal with a time width of T1 as shown in the circle in c in Figure 2. A second pulse signal of T ₂ is output. Furthermore, if the input from the monostable multivibrator MM to the first NAND gate 5 is low level, the first NAND gate 5 outputs the monostable multivibrator as shown by ○c in b in Fig. 2.
As long as the output of the MM is at a low level, a third pulse signal having a sufficiently long period of time at a high level is output, and during this period, the output of the pulse signal from the inverter 6 is stopped.

Furthermore, when the amount of current flowing through the heating element 3 is less than the preset amount of current, the detection level of the current transformer 4 is small, and the level at the connection point of resistors 30 and 31 is higher than the level at the connection point of diodes 28 and 29, and the comparator 32 of the comparison circuit COM The output becomes low level. At this time, the output of the NAND gate 34 is at a high level regardless of the input of the pulse signal from the NAND gate 5, the output of the NAND gate 35 is at a low level, and the monostable multivibrator MM does not operate, keeping its output at a high level. Heating element 3
When the amount of current flowing through exceeds the set current amount, the detection level of the current transformer 4 increases, and the level at the connection point of the diodes 28 and 29 becomes higher than the level at the connection point of the resistors 30 and 31, and the output of the comparator 32 of the comparison circuit COM goes high. level. Therefore, the NAND gate 34 output is the first one from the NAND gate 5.
When the pulse signal is input, it becomes low level and the output of NAND gate 35 becomes high level, and the monostable multivibrator MM operates at a cycle based on the time constant of capacitor 37 and resistor 38, and keeps the output low level for a certain period of time. Hold.

Therefore, when the power supply 1 is turned on, the first gate trigger circuit GT ₁ is activated by the first pulse signal from the oscillation circuit OSC to adjust the conduction angle of the control rectifier 2.
Continuity control at 90 degrees and second gate trigger circuit
GT ₂ is operated by the second pulse signal from the oscillation circuit OSC to control the conduction of the control rectifying element 2 at an arbitrary conduction angle. That is, the controlled rectifying element 2 is controlled to be conductive at a conduction angle of 90 degrees for a time _T1 , and is controlled to be conductive at an arbitrary conduction angle for a time _T2 , and this is repeated alternately. For example, if you turn on the power supply 1 while the heating element 3 is cold, and the second gate trigger circuit GT ₂
If the conduction angle set by
Since the resistance value of is small, a large current flows. This large current is immediately detected by the current transformer 4, and the monostable multivibrator MM operates at the timing when the first pulse signal is output from the oscillation circuit OSC, converting the first pulse signal of the oscillation circuit OSC into the third pulse signal. The second pulse signal is converted into a pulse signal and the output of the second pulse signal is stopped. However, from then on, the conduction of the controlled rectifying element 2 is controlled only by the first gate trigger circuit GT ₁ at a conduction angle of 90 degrees.
The amount of current applied to the heating element 3 is suppressed to 1/√2 of that during full-wave energization.

Therefore, when an appliance equipped with such a heating element 3 is used at home, it is possible to prevent as much as possible the occurrence of inconveniences such as a large current flowing when the power is turned on, exceeding the household current capacity and tripping the breaker. .

[Effect of idea]

As explained above, according to this invention, the temperature of the heating element formed by a positive temperature coefficient thermistor is low, and even if electricity is started when the internal resistance of this heating element is low, the large current flowing at that time is detected and immediately It is possible to provide a heating element control device that can suppress the amount of current and eliminates the risk of a large current continuing to flow.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an embodiment of this invention, Figure 2 is a circuit diagram showing an embodiment of this invention.
The figure is a waveform diagram showing the output waveform of the oscillation circuit in the same embodiment. DESCRIPTION OF SYMBOLS 1...First AC power supply, 2...Bidirectional three-terminal control rectifier, 3...Heating element formed by a positive temperature coefficient thermistor, 4...Current transformer, _GT1 ...First gate trigger circuit, _GT2 ...First 2 gate trigger circuit,
OSC...oscillation circuit, COM...comparison circuit, MM...monostable multivibrator.

Claims (1)

[Scope of utility model registration request] An AC power supply, a heating element formed by a positive temperature coefficient thermistor connected to the AC power supply through a three-terminal control rectifier in series, and a current detector that detects the amount of current flowing through the heating element. , a comparison circuit that compares the output level of the current detector with a preset setting level and outputs a signal when the output level of the current detector exceeds the setting level;
One input terminal of a first NAND gate is connected to the output terminal of the non-stable multivibrator, and an inverter is connected to the output terminal of the first NAND gate, and the output terminal of the first NAND gate has a pulse width of at least an oscillation circuit that alternately generates a first pulse signal having a longer pulse width than the period of the AC power source and a second pulse signal having a longer pulse width than the first pulse signal at the output end of the inverter; a first gate trigger circuit that is supplied with one pulse signal and controls conduction of the three-terminal control rectifying element at a relatively small predetermined conduction angle in synchronization with the cycle of the AC power supply only during the supply period of the first pulse signal; and a second gate trigger that is supplied with the second pulse signal and controls conduction of the three-terminal control rectifier at an arbitrary conduction angle in synchronization with the cycle of the AC power supply only during the supply period of the second pulse signal. a second NAND gate having one input terminal connected to the output terminal of the comparison circuit and the other input terminal connected to the output terminal of the first NAND gate; and an input terminal of the second NAND gate. The output terminal of the first NAND gate is connected to the other input terminal of the first NAND gate, and the output terminal of the comparison circuit allows the first pulse signal outputted from the oscillation circuit to be adjusted to a width sufficiently larger than the pulse width of the first pulse signal outputted from the oscillation circuit. A heating element control device comprising: a monostable multivibrator that supplies a long third pulse signal to the first gate trigger circuit and stops outputting the second pulse signal.