JPH0975220A - Electric water heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electric water heater which is low in cost and which does not generate much heat in the circuit base board and which does not bring thermal breakage in the switching part or the like when a current fuse is not molten with troubles, by providing a Darlington connection part connected to a condenser to act the switching motion by means of the output of controller. SOLUTION: A Darlington connection part 31 is constituted of a first transister 25, a second transister 28, and resistances 27, 29, 30. A controller 42 generates a basic voltage by a basic voltage circuit 39 and generates divided potentials by a potential dividing circuit 36. Both voltages are compared by a comparison circuit 35 and the Darlington connection part 31 is controlled on the basis of the result. The switching control is exterted so as to put on or off the Darlington connection part 31 in accordance with the divided potential smaller than the basic voltage or larger than that. Rectifying elements 21, 22, the condenser 43, and a heat-retaining heater 4 are connected to an AC source 17 in series.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electric water heater.

[0002]

2. Description of the Related Art Conventionally, a water heater of this type is disclosed in, for example, Japanese Patent Publication No. 6-85736. According to this publication, a relay and a heater are connected in series to an AC power supply, and a microcomputer is connected to the AC power supply via a power supply circuit. A control signal is output from the microcomputer to the relay according to the input of the temperature sensor.

[0003]

However, since this water heater requires a low DC voltage with little voltage fluctuation for the microcomputer, the power supply circuit described above requires a transformer, a rectifying circuit, and a smoothing circuit. There is a first drawback that goes high.

Therefore, the means for disposing the metal oxide resistor on the circuit board and stepping down the AC power source has a second drawback that the resistor requires a large space on the circuit board and the amount of heat generated by the resistor is large.

Therefore, the present inventor connected a rectifying element and a capacitor to the heat retention heater, and connected a switching unit (for example, a control transistor) to the capacitor via a diode to manufacture a power supply circuit. In the case where a failure occurs in which the heat-retaining heater wire and the boiling water heater wire come into contact with each other inside the heater, a current fuse is provided in the power supply circuit to protect the rectifying element and the like. However, the effective current of the power supply circuit in the normal state is about 0.45 A, and the fusing current of the current fuse is about 1 A in consideration of the margin. However, due to the contact state between the heat retention heater wire and the water heater wire, the effective current of the power supply circuit becomes less than 1 A, the current fuse does not melt, and a relatively large current flows, especially the control transistor heats up and is destroyed by heat. There is a drawback of.

Therefore, in consideration of the above-mentioned conventional drawbacks, the present invention is one in which the cost is low, the heat generation amount of the circuit board is small, and there is a failure in which the heat-retaining heater and the boiling water heater come into contact with each other and the current fuse is not blown. Also, to provide an electric water heater in which a switching unit or the like is not thermally destroyed.

[0007]

In order to solve the above problems, the present invention provides a water heater connected to an AC power source, a rectifying element, a capacitor, and a warming heater connected in series to the AC power source, and a capacitor thereof. And a Darlington connection portion connected to the capacitor and switched by the output of the control portion.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view of an electric water heater according to the present embodiment, and FIG. 2 is an electric circuit diagram of the electric water heater. In these drawings, the frame 1 has a cylindrical shape, and the container 2 has a bottomed cylindrical shape which is installed in the frame 1. Heater set 3 contains content liquid (water, etc.)
It is composed of a warming heater 4 and a water heater 5 which are closely attached to the bottom of a container 2 for storing The back cover 6 is fixed to the lower part of the frame 1, and a storage space 7 is provided between the back cover 6 and the bottom wall of the container 2.

The hot water supply pipe 8 has one end communicating with the container 2 and the other end led out of the frame 1. The hot water supply pump 9 is located in the path of the hot water supply pipe 8, is arranged and fixed in the storage space 7, and is driven by the DC motor 10. The storage box 11 stores control components for controlling the heat retention heater 4, the water heater 5, and the hot water supply pump 9.

The temperature sensor 12 is closely attached to the outer bottom surface of the container 2, the lid 13 is provided on the upper portion of the frame 1 so as to be openable and closable, and the hot water supply switch 14 is provided on the upper portion of the main body. The reboil switch 15 is provided at the bottom.

Next, the electric circuit will be described with reference to FIG. The relay contact 16 is connected in series to the water heater 5, and the series circuit is connected to the AC power supply 17. The fusing current of the first current fuse 18 is relatively high at about 15 A, and one end thereof is connected to one end of the AC power supply 17.

The surge absorbing element 19 acts as a high resistance when a voltage of about 100 V is applied, and acts as a low resistance when a medium-scale surge voltage is applied, and absorbs energy due to the surge voltage. The surge absorbing element 19 and the capacitor are connected in parallel, one end of the parallel circuit is connected to the other end of the first current fuse 18, and the other end of the parallel circuit is connected to the other end of the AC power supply 17.

The second current fuse 20 has a fusing current of about 1 A.
Is relatively low, one end of which is connected to the other end of the first current fuse 18 and the other end of the second current fuse 20 is
1 (for example, a diode) is connected to the anode.
The cathode of the rectifying element 21 is connected to the anode of the rectifying element 22, and the intermediate point between the two elements 21, 22 is the first lead wire 23.
It is connected to the. The cathode of the rectifying element 22 is connected to the second lead wire 24.

The collector of the first transistor 25 is connected to the first lead wire 23, the emitter is connected to the third lead wire 26, and the base is connected to the base of the second transistor 28 via the resistor 27. Second transistor 28
Has a collector connected to the first lead wire 23, an emitter connected to a lead wire connecting the base of the first transistor 25 and the resistor 27, and a third lead wire 26 via the resistor 29.
It is connected to the. Further, one end of the resistor 27 is connected to the second lead wire 24 via the resistor 30. The above-mentioned first transistor 25, second transistor 28, resistors 27, 2
The Darlington connection portion 31 is constituted by 9 and 30.

The output terminal of the comparator (comparator) 32 is connected to the midpoint between the resistors 27 and 30, and the comparator 32 is (+).
It has an input terminal and a (-) input terminal. The resistor 33 and the diode 34 are connected in series and connected to the output terminal of the comparator 32, and the comparator 32, the resistor 33, and the diode 34 form a comparison circuit 35.

The voltage dividing circuit 36 is composed of resistors 37 and 38 connected in series. One end of the resistor 37 is connected to the second lead wire 24.
And one end of the resistor 38 is connected to the third lead wire 26. The middle point of the resistors 37 and 38 is connected to the (+) input terminal of the comparator 32, and the middle point is connected to one end of the resistor 33.

The reference voltage circuit 39 comprises a resistor 40 and a Zener diode 41 connected in series, one end of the resistor 40 is connected to the second lead wire 24, and one end of the Zener diode 41 is connected to the third lead wire 26. Has been done. The intermediate point between the resistor 40 and the Zener diode 41 is the comparator 3
2 is connected to the (-) input terminal. With the above-mentioned comparison circuit 35, voltage dividing circuit 36, and reference voltage circuit 39, the control unit 4
2 are configured.

One end of the capacitor 43 has a second lead wire 24.
, And the other end is connected to the third lead wire 26. As described above, the rectifying elements 21 and 22, the condenser 43, and the heat retention heater 4 are connected in series to the AC power supply 17.

The control unit 42 is connected in parallel to the capacitor 43, the Darlington connection unit 31 is also connected in parallel to the capacitor 43 via the rectifying element 22, and is connected to the control unit 42 via the output terminal of the comparator 32. .

The relay circuit 44 comprises a coil and a diode connected in parallel. One end of the relay circuit 44 is connected to the collector of the transistor 45, and the other end is connected to the third lead wire 26 via a resistor. . Transistor 4
The base of 5 is connected to the midpoint of resistors 46 and 47.

The pump circuit 48 is one in which the hot water supply switch 14 and the motor 10 are connected in series, one end of which is connected to the collector of the transistor 49, and the other end of which is connected to the third lead wire 26. . The base of the transistor 49 is connected to the midpoint between the resistors 50 and 51.

The terminal P1 of the microcomputer 52 is connected to the resistor 47, and the terminal P2 is connected to the resistor 51. One end of the fourth lead wire 53 is connected to the second lead wire 24, and the other end of the fourth lead wire 53 is connected to the microcomputer 5
2 terminals P3 and P4. The other end of the fourth lead wire 53 is connected to the heat retention lamp 54 through a resistor to connect to the terminal P.
5, to the terminal P6 through the water heater lamp 55 and the resistor,
And it is connected to the terminal P7 via the reboil switch 15 and a resistor.

The collector of the transistor 56 is connected to the third lead wire 26, the emitter is connected to the fifth lead wire 57, and the base is connected to the second lead wire 24 via the Zener diode 58. A resistor 59 is connected between the third lead wire 26 and the intermediate point between the base of the transistor 56 and the Zener diode 58. The capacitor 60 is connected between the second lead wire 24 and the fifth lead wire 57. The portion of the ground symbol connected to each terminal of the microcomputer 52 indicates that it has the same potential as the fifth lead wire 57.

One end of the temperature sensor 12 has a fourth lead wire 5
3, the other end of the temperature sensor 12 is connected to the terminal P8 of the microcomputer 52 via the resistor 61,
Further, it is connected to the same potential portion as the fifth lead wire 57 via the resistor 62. These components constitute the electric water heater according to the present embodiment.

Next, the operation of the electric water heater will be described again with reference to FIGS. 1 and 2. In these figures, first, water is put in the container 2, and the power plug of the electric water heater is inserted into a power outlet (not shown).

When the AC power source 17 has a positive potential, the first current fuse 18, the second current fuse 20, the rectifying elements 21, 2
Current flows through the second and second lead wires 24, the capacitor 43, the third lead wire 26, and the heat retention heater 4, and the voltage across the capacitor 43 starts to rise. Then, the reference voltage circuit 39 of the control unit 42 generates a reference voltage, and the reference voltage (that is, the Zener voltage of the Zener diode 41) is input to the (−) input terminal of the comparator 32.

Further, the voltage dividing circuit 36 of the control unit 42 generates a divided voltage, and the divided voltage is (+) of the comparator 32.
Input to the input terminal. At this time, since the divided voltage is less than the reference voltage, the comparator 32 outputs the “L” signal, and the output terminal of the comparator 32 is the ground line (not shown) in the comparator 32.
To conduct.

As a result, a current flows through the second lead wire 24, the resistor 30, and the ground wire in the comparator 32, and no current flows through the base of the second transistor 28. Therefore, the second transistor 28 is turned off, no current flows through the base of the first transistor 25, and the first transistor 25 is also turned off. As a result, the voltage across the capacitor 43 and the divided voltage gradually increase.

Next, when the divided voltage becomes higher than the reference voltage, the output of the comparator 32 becomes "H" and the output terminal of the comparator 32 is opened. As a result, current flows through the resistor 30 to the base of the second transistor 28, and the second transistor 2
8 turns on. Then, a current flows to the base of the first transistor 25 and the first transistor 25 is turned on, and the current is mainly the first current fuse 18, the second current fuse 20, the rectifying element 21, the first lead wire 23, and the first transistor 25.
And flows through the heat retention heater 4. Therefore, there is no charging current to the capacitor 43, and the voltage across the capacitor 43 and the divided voltage start to drop.

Further, the voltage across the capacitor 43 decreases,
When the divided voltage becomes lower than the reference voltage, the output of the comparator 32 is inverted to "L". As a result, as described above, the resistance 30
A current flows through the ground wire in the comparator 32, the second transistor 28 and the first transistor 25 are turned off, and the voltage across the capacitor 43 and the divided voltage rise again.

In this way, the control unit 42 controls the reference voltage circuit 39.
Generates a reference voltage, the voltage dividing circuit 36 generates a divided voltage, the comparison circuit 35 compares the two voltages, and controls the Darlington connection 31 based on the result. That is, switching control is performed so that the Darlington connection portion 31 is turned off or on depending on whether the divided voltage is less than or equal to the reference voltage.

Since the water temperature in the container 2 is low when the power is turned on, the resistance value of the temperature sensor 12 is large. And
When the voltage for this large resistance value is input to the terminal P8 in the microcomputer 52, the microcomputer 52 outputs the "L" signal to the terminal P1. As a result, the lead wire connected to the terminal P1 has a low voltage, the transistor 45 is turned on, the relay circuit 44 is energized, the relay contact 16 connected to the relay circuit 44 is turned on, and the water heater 4 is energized. Then, both the heat retention heater 4 and the water heater 5 generate heat to perform water heating.

Next, when the temperature of the hot water rises to almost the boiling temperature, the resistance value of the temperature sensor 12 decreases, and the output to the terminal P8 of the microcomputer 52 reaches a predetermined value.
The microcomputer 52 determines that it is "boiling", and the terminal P
The “H” signal is output to 1. As a result, the voltage of the lead wire connected to the terminal P1 rises, the transistor 45 is turned off, the relay circuit 44 is de-energized, the relay contact 16 is turned off, the water heater 5 stops heating, and the temperature is maintained. Move.

When the user needs hot water and turns on the hot water supply switch 14, since the microcomputer 52 outputs the "L" signal to the terminal P2 when the temperature is kept warm, the lead wire connected to the terminal P2 has a low voltage. Then, the transistor 49 is turned on, the pump circuit 48 is energized, the DC motor 10 is energized, and hot water discharge is started.

The heat retaining heater 4 is, for example, about 32W.
Power consumption and the resistance value is about 150 ohms. The electric water heater 5 has a power consumption of, for example, about 840 W and a resistance value of about 11 ohms. When the electric water heater is operating normally, the current (effective value) flowing through the heat retention heater 4 or the like during heat retention is about 0.45A. This is the end of the description of the normal operation of the electric water heater.

Next, in the case of the heater set 3 in which the warming heater 4 and the boiling water heater 5 are integrated, it is conceivable that the warming heater wire and the boiling water heater wire come into contact with each other inside the heater set 3 to cause a failure. In this failure mode, the current flowing through the circuit changes variously depending on the contact point, but the case where the point is A1 and B1 located far from the common line of both heaters 4 and 5 will be described.

In this case, for example, from one end of the AC power supply 17, the first current fuse 18, the second current fuse 20, the rectifying element 21, the first lead wire 23, the first transistor 25, the third lead wire 26, the A1 portion and B1. Most of the current instantaneously flows to the other end of the AC power supply 17 through the portion and the water heater 5.

In the above circuit, since a current flows through the water heater 5 having a relatively small resistance value of about 11 ohms,
The current value (effective value) is about 8.4A. At this time, the second current fuse 20 (fusing current 1A) connected to this circuit
The circuit is cut off to the safe side by melting. In the case of such contact and failure, it is more advantageous to reduce the fusing current of the second current fuse 20, but the effective current value under normal conditions is 0.45A (peak current value is about 0.9A). Therefore, the fusing current cannot be set to less than 1 A in consideration of the premature disconnection during normal operation and considering the margin.

Next, A2 where the contact points of both heaters 4 and 5 are relatively close to the common line of both heaters 4 and 5,
The case of B2 will be described. In this case, the first current fuse 18, the second current fuse 20, the rectifying element 21, the first lead wire 23, the first transistor 25, the third lead wire 26, the heat retaining heater 4 (between A1 and A2), and A2 to B2. An electric current mainly flows to the space and the water heater 5 (from B2 to the other end). Suppose that the current value is 0.9 A (effective value).

At this time, the current between the collector and the emitter of the first transistor 25 is 0.9 A (effective value), and the peak current value is 1.8 A. And the first transistor 2
5 and the current amplification factor HFE of the second transistor 28 (value obtained by dividing the current value of the emitter by the current value flowing through the base) are set to 50 and 100, respectively. As a result, the base current of the first transistor 25 (current flowing from the base to the emitter)
Has a peak value of 1.8 A / 50 = 36 mA.

When the above circuit is energized,
Since the base current of mA is supplied by the second transistor 28 and the first transistor 25 is in the “saturation region”,
The voltage between the collector and the emitter of the first transistor 25 is a comparatively small value of several tens of mV. Therefore, even in the case of a contact failure of the heater wire in which the current fuse 20 is not blown, the Darlington connection part 31 operates in the saturation region (the resistance of the transistor itself becomes small), so that the first transistor 25 can be prevented from generating heat and destroyed. It can be prevented.

The base current of the second transistor 28 is relatively small at 1.8 A × 1/50 × 1/100 = 0.36 mA. This base current is supplied via the resistor 30. The above-described operation has been described with the output of the comparator 32 being "H" and the Darlington connection 31 being on.

When the Darlington connection 31 is turned on in this manner, the charging current of the capacitor 43 is not supplied and the voltage across the capacitor 43 drops. Then, as described above, when the divided voltage becomes lower than the reference voltage, the output of the comparator 32 is inverted to “L”, and the current flows through the resistor 30 to the ground line in the comparator 32.

At this time, the output current of the comparator 32 (current drawn into the ground line) is relatively small, about 0.36 mA, which is substantially equal to the base current of the second transistor 28 described above. Therefore, as the comparator 32, for example, one having a comparatively small maximum rating of output current of 10 mA can be selected, and a standard product having a low cost can be used.

Further, in the structure in which the transistors are provided in one stage as the switching portion as in the conventional case, HFE = 5 so that the transistors operate in the saturation region in order to prevent heat generation of the transistors.
By choosing 0, a base current of 36 mA is obtained. However, as described above, it is necessary for the comparator to have a large output current of about 36 mA at the time of "L" output, which causes a drawback that a standard product whose cost is low cannot be used.

On the other hand, in the present invention, the switching unit is constituted by the Darlington connection unit 31, and the current amplification factor HF is set.
Use the fact that E becomes large. That is, by sufficiently securing the base current of the first transistor 25 and using it in the saturation region, heat generation of the first transistor 25 is suppressed. Since the HFE is large, the base current of the second transistor 28 is made small, and the comparator 3 which is approximately equal to the base current
The output current at the time of "L" output of 2 is reduced. as a result,
As the comparator 32, a standard product whose cost is low can be used.

In the power supply circuit 63 including the rectifying elements 21 and 22, the Darlington connection part 31, the control part 42, the condenser 43, and the warming heater 4, the warming heater 4 has a relatively low impedance (about 150 ohms). Therefore, even if the relay circuit 44 as the load circuit, the pump circuit 48, and the microcomputer 52 are all connected, a sufficient current can be supplied to each of the circuits 44, 48, and 52.

A half-wave current flows through each circuit of the rectifying elements 21 and 22, the condenser 43 and the heat retaining heater 4, or the rectifying element 21, the first transistor 25 and the heat retaining heater 4, and the heat retaining heater 4 has a substantially constant power. (For example, 32 W) is consumed. As a result, in an electric water heater having a capacity of about 2.2 liters, the heat insulation power is appropriate. The power supply circuit 63 is configured by using the warming heater 4 as a step-down resistor.
Therefore, since the metal oxide resistor as the step-down resistor is not arranged on the circuit board as in the conventional case, the circuit board does not generate heat due to this resistance.

[0049]

As described above, according to the present invention, the voltage from the AC power source is rectified by the rectifying element and stepped down by the heat insulation heater, the voltage across the capacitor rises, and the control unit controls the divided voltage of the capacitor and the reference voltage. And compare both,
When the divided voltage exceeds the reference voltage, the Darlington connection is turned on. As a result, a current flows through the Darlington connection part connected in parallel with the capacitor, the charging current to the capacitor stops flowing, the voltage across the capacitor drops, and the divided voltage also drops.

When the divided voltage becomes less than the reference voltage, the Darlington connection section is turned off by the control section. As a result, the capacitor charges and the voltage across it rises again.
In this way, the control unit switches the Darlington connection so as to keep the voltage across the capacitor substantially constant, so that a substantially constant voltage can be supplied to the relay circuit, the pump circuit and the microcomputer connected to the capacitor.

As described above, since the power supply circuit is composed of the rectifying element, the capacitor, and the heat-retaining heater, an expensive power supply transformer as in the prior art is not required, so that an inexpensive power supply circuit with less voltage fluctuation can be obtained. That is, since the relay circuit, the motor circuit, and the power supply circuit for supplying a voltage to the microcomputer can be shared, the manufacturing cost can be reduced as compared with the conventional product in which the rectifying circuit and the smoothing circuit are individually provided. Further, unlike the conventional case, since it is not necessary to use a large metal resistor, a relatively small circuit board can be used, and the temperature rise of the circuit board is small.

Further, in the present invention, when the heat retention heater and the water heater are in contact with each other and the current fuse does not melt, a Darlington connection is provided to secure a sufficient base current for the first transistor and use it in the saturation region. This suppresses heat generation of the first transistor. The Darlington connection reduces the base current of the second transistor in the Darlington connection. As a result, the output current at the time of "L" output of the comparator in the control unit, which is substantially equal to the base current, can be reduced, so that a low-cost standard product can be used as the comparator.

[Brief description of drawings]

FIG. 1 is a sectional view of an electric water heater according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of the electric water heater.

[Explanation of symbols]

 4 Heat insulation heater 5 Water heater 21, 22 Rectifier element 31 Darlington connection part 42 Control part 43 Capacitor

Front page continuation (72) Inventor Kazuki Asai 3-201 Minamiyoshikata, Tottori City, Tottori Prefecture Tottori Sanyo Electric Co., Ltd.

Claims (1)

[Claims] 1. A boiling water heater connected to an AC power supply, a rectifying element, a capacitor, and a warming heater connected in series to the AC power supply, a control unit for detecting the voltage of the capacitor, and a capacitor connected to the capacitor and An electric water heater equipped with a Darlington connection that switches according to the output of the control unit.