KR890003277B1 - Electric heather - Google Patents

Abstract

The two heaters with two changeover switches are connected in parallel for mains voltages in the 100V range and in series for voltages in the 200V range. One heater is connected between the neutral line and a triac, the other side of the triac being connected to the live rail. The second heater is connected between live and normally closed relays which serve to operate the heaters in parallel. The voltage detecting circuit causes a transistor to energise the relay and operate the heaters in series when the main voltage reaches 200-240V. Alternatively two relays are used for the switching.

Description

Electric heater

1 is a cross-sectional view of the hair dryer of the present invention.

Figure 2 is an enlarged perspective view of the main portion of the present invention.

3 is an electrical circuit diagram of the present invention.

4 is a cross-sectional view of a hair dryer of another embodiment.

5 is an electrical circuit diagram of another embodiment.

6 is an electric circuit diagram in which the protection resistor of the present invention is inserted.

7 is an electric circuit diagram incorporating a protective resistor of another embodiment.

8 is an electric circuit diagram of a conventional electric heater.

* Explanation of symbols for main parts of the drawings

1,51 hair dryer 2,57 discharge port

3,55: Inlet 4,54: Handle

5,52: Case 6,60: Heater unit

7: insulation board 8,61: first heater

6,62: second heater 10: limiter

11: motor holder 12,58: motor

14: paste plate 15,71: noise prevention capacitor

16: rectifying bridge diode 19: partition wall

20,53: space 21: edge end

22,63: print engine 25,78: drive circuit

26,81: SCR (Dy Lister) 27,64,65: Relay Coil

28,65b: relay switch 30: power switch

32: half-wave rectifier diode 33: voltage divider

34: voltage divider resistance 35: constant voltage element

36: transistor 37: bias resistor

40: triac 42: smoothing capacitor

43: constant voltage diode 74: temperature fuse

The present invention relates to an electric heating device for automatically connecting or connecting a plurality of heaters (HEATER) in accordance with the power supply voltage supplied. In general, although the commercial voltage of each country in the world is different, it can be roughly divided into 100V countries and 200V countries.

Conventionally, electric heaters such as hair dryers, which are carried as essential items by overseas travelers, have a fixed operating voltage. Therefore, if the voltage is used in a different country, the heater may not be heated or heated sufficiently. There is a drawback that it is not suitable for use as it occurs. For this reason, the structure of the electric heating apparatus which has two heaters, and connects each heater in parallel in case of a commercial voltage of 100V using a manual switching switch, and connects in series in case of 200V is proposed. 81-50365, Lab 83-18804).

8 shows this configuration, and one end of the first load 101 is connected to the one pole 105a of the power supply with the main switch 107 interposed therebetween, and the second load 102 is connected. One end of is connected to the other electrode 105 side of the power supply.

The common terminal 103C of the first switch 103 is connected to the other end of the first load, and the first contact 103a is connected to the other electrode 105b side of the power supply. The second contact 103b is connected to the second contact 104b of the second switch 104, and the first contact 104a connects the main switch 107 to the one pole 105a of the power supply 105. It is connected to. The common terminal 104C of the second switch 104 is connected to the other end of the heater 102. When the 1st and 2nd switches are interlocked and the 1st contact 103a of the 1st switch 103 is closed, the 1st contact 104a of the 2nd switch 104 will be closed simultaneously, and a 1st switch will be When the second contact 103b of 103 is closed, the second contact 104b of the second switch 104 is closed.

According to this configuration, the manual switch is connected in parallel by pushing the switch to the first contact side, and the positive switch is connected in series by pushing the switch to the second contact side.

However, when the user switches to a voltage different from the power supply voltage that is supplied by mistake, sufficient voltage is not supplied to the load or overvoltage is applied to cause redness or disconnection. Therefore, the user had to check the switching switch in advance, which was complicated. Thus, it has been proposed to switch automatically. This is a voltage drop resistor connected in series to one load, and when the power supply voltage is less than or equal to a predetermined value, a short-circuit as a voltage dropping switching element is shorted so that a full voltage is applied only to the load.

When the power supply voltage is higher than or equal to the predetermined value, the short-circuit state is canceled so that the power supply voltage is applied to the voltage drop resistor and the load (Patent No. 81-82920). The determination of the angle at which the power supply voltage is higher than or equal to the predetermined value or lower is automatically performed by the constant voltage diode.

In the above configuration, switching to the power supply voltage can be realized.

However, there is a drawback that the voltage drop resistor consumes power in vain. For example, even if heat generated from the voltage drop resistor can be effectively used, power consumption at high voltage and low voltage is different so that a certain amount of heat is not emitted.

Therefore, the above structure can be used favorably for low power consumption devices such as watches, and can be said to be inadequate for high heat generation devices such as electric heaters. In the conventional electric heating apparatus shown in FIG. 8, since the switches are simultaneously switched, there is a point in time at which the movable contact plates of both switches are positioned between the first contact point and the second contact point, respectively. At this time, an arc ARC was generated between the first contact point and the second contact point of the first switch and between the first contact point and the second contact point of the second switch through the movable contact plate, thereby causing a short circuit. If such arc generation is repeated, the life of the switch is shortened.

In particular, in a small electric heating apparatus such as a hair dryer, the switch must also be used because the installation space of the switch is small. In this case, since the distance between the first contact point and the second contact point becomes considerably shorter, the arc is easily generated. Moreover, not only in switch switching, but also when electric power has a strong impact on the heater body while the power supply is turned on, there are cases in which a kind of contact plate of the switch vibrates and an arc occurs between the contacts, causing a short circuit.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic switching type electric heating device which prevents misoperation of a switch by switching so that a plurality of heaters are connected in series or in parallel in accordance with a supplied power supply voltage.

Still another object of the present invention is to provide an electric heating apparatus in which an automatic switching type electric heater is provided so that an arc does not occur between the contacts even when the switch is switched so that the circuit is not shorted. It is still another object of the present invention to provide an electric heating device in which an arc does not occur and a short circuit occurs between the contacts even when the contact plate is broken by a strong shock or the like while the power is on.

The above object is achieved by providing an electric heater having a first heater, a second heater, and a plurality of switches for connecting each heater in series or in parallel with respect to a power source, and having the following features. The electric heater has switch driving means for driving the switches in series when the power supply voltage is higher than or equal to a predetermined value, and connecting the heaters in series when the power supply voltage is lower than or equal to the predetermined value.

In the electric heating device of the above configuration, when the power supply voltage supplied is equal to or greater than a predetermined value, the driving means drives each switch to connect each heater in series. When the power supply voltage is lower than or equal to the predetermined value, the drive circuit drives each switch to connect each heater in parallel.

Moreover, the said objective is achieved by providing what has the following characteristics as an electric heating apparatus which has a 1st heater, a 2nd heater, and the some switch which connects each heater in series or parallel with respect to a power supply. The plurality of switches are formed from an on / off switch and a switching switch, one end of the first heater is connected to one pole of the power supply, and the other end of the first heater is always closed. It is connected to the other pole of a power supply via an opening / closing switch.

One end of the second heater is connected to the other pole side of the power supply, and the other end of the second heater is connected to the common terminal of the switching switch. The first contact of the upper and lower ends of the switching switch is connected to the one pole side of the power supply, and the upper second contact is connected to the other end of the first heater. Furthermore, it has a drive means which turns off the switching switch when the power supply voltage is more than a predetermined value, and then switches the switching switch to the second contact side.

In the electric heating apparatus of the above structure, when the power supply voltage is less than or equal to a predetermined value, both heaters are kept in parallel connection state, but when the power supply voltage is greater than or equal to a predetermined value, the drive circuit first turns off the opening and closing switch. At this time, since the first heater is not energized, both ends of the first heater are coin operated. Therefore, the 2nd contact point and the 1st contact point of a switching switch mutually become coin positions. Thereafter, the drive circuit attaches the switching switch contact plate from the first contact side to the second contact side. Therefore, no arc occurs during switching.

The above object is also an electric heating apparatus having a first heater, a second heater, and a plurality of switches for connecting each heater in series or in parallel with respect to a power source, and achieving the following characteristics. do. Insertion of the protection degradation in series in at least one section selected from a group consisting of a section in which the switch and the power supply are connected without passing through the heater and a section in which each switch and the other switch are connected without passing through the heater It is.

In the electric heating apparatus described above, even when an impact is applied while the power is on, the movable contact plate may vibrate and limit the current flowing by the protection resistors connected in series even when an arc occurs.

The features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings. A first preferred embodiment of the electric heating apparatus of the present invention will be described below with reference to FIGS. 1 to 3. This embodiment relates to a hair dryer, in particular, a so-called curl dryer that connects an accessory such as a comb or a brush to a rod-shaped dryer main body to exercise curl of the hair.

1 is a cross-sectional view of the hair dryer 1 of the present invention, Figure 2 is an enlarged perspective view of the main portion of the present invention. The hair dryer 1 has the elongate cylindrical case 5, the discharge port 2 is provided in the front surface of the case 5, and the inlet port 3 is provided in the rear surface. A handle 4 is formed on the inlet port side of the cylindrical case 5. The heater unit 6 is disposed on the discharge port side in the cylindrical case 5. The heater unit 6 includes an insulated substrate 7 combined in a cross shape, a first heater 8 and a second heater 9 wound around the engine, and a temperature rise preventing device, or It has a limiter 10.

A MOTER HOLDER 11 is disposed between the inlet port 3 of the cylindrical case 5 and the heater unit 6, and the MOTA 12 is fixed by the MOUT HOLDER 11. . The wing | blade 13 is attached to the mouta shaft. At the end of the heater unit side of the motive 12, as shown in FIG. 2, a noise preventing capacitor 15, a power supply diode 16 and a triac 40 are attached.

The outer diameter of the pasting substrate 14 is set to be equal to or slightly smaller than the outer diameter of the mutator 12 in order to reduce the wind path resistance. The triac 40 protrudes most of it from the outer periphery of the substrate to be cooled by hitting the wind flowing through the outer wall of the motha 12. Numeral 14a is a fixing plate fixing screw.

In the cylindrical case 5, a partition wall 19 integrally provided with the case forms a space 20.

The edge end 21 on the right side of the partition wall 19 is inclined to the inner wall side of the cylindrical case 5, and the wind induced from the intake port 3 is collected to force the triac.

A printed board 22 is attached to the space 20. Electronic components are placed on the printed board 22. Next, the electric circuit of the hair dryer will be described. 3 shows the electric circuit of the present invention. An AC voltage of 100-200V or 200-240V is supplied from supply terminals 24a and 24b of the AC power supply. The supplied AC voltage is sandwiched between the temperature increase prevention device 10 and the power switch 30, and supplied to the motor 12, the heaters 8, 9, and the drive circuit 25 as drive means. The dotted line 18 surrounds the mouta and the mouta driving circuit. The motor drive circuit is formed as a rectifying bridge diode (BRIDGE DIODE) 16 and a noise suppressing capacitor 15 which are connected in parallel with a part of the first heater 8 to supply a DC output to the motor 12. .

The half-wave rectifying diode 32 supplies a direct current to the driving circuit. The dotted line 17 surrounds the drive circuit 25, the triac 40 as an opening / closing switch, and the RELAY switch 28 as a switching switch. A constant voltage diode 43 is connected between the step-down resistor 41 from the input terminal 29a of the drive circuit 25. A relay coil 27 and an SCR 26 connected in series with each other in parallel with the constant voltage diode 43 are connected. By this connection, the relay coil 27 operates by a constant voltage. Reference numeral 42 is a smoothing capacitor.

The voltage divider 33 and 34 connected in series with each other are connected to the input terminals 29a and 29b of the drive circuit 25. The connection point of the voltage divider resistors 33 and 34 is connected to the gate GATE of the SCR 26 with the constant voltage element 5 interposed therebetween. The voltage division ratio of the voltage divider resistors 33 and 34 is set such that the constant voltage element 35 reaches the Zener voltage ENER VOLTAGE when the power supply voltage becomes 150 V or more. In addition, the connection point between the relay coil 27 and the SCR 26 is connected to the base of the transistor 36 as an electronic switching element with a bias resistor 37 interposed therebetween. .

A resistor 31 is connected between the base of the transistor 36 and the input terminal 26b. The relay coil 27 has a current flowing through the resistors 37 and 31, but the resistance values of the resistors 37 and 31 are set so that the current value does not reach the current value for driving the relay coil 27. The collector COLLECTER of the transistor 36 is connected to the input terminal 29a with the resistors 38 and 39 interposed therebetween. An emitter (EMITER) of the transistor 36 is connected to the input terminal 39b. The connection point of the resistor 38 and the resistor 39 is connected to the gate of the triac 40. One end of the heater 9 is connected to the power supply terminal 24b, and the other end is connected to the power supply terminal 24a with the triac 40 interposed therebetween.

One end of the heater 8 is connected to the power supply terminal 24a, and the other end is connected to the common terminal 28C of the relay switch 28. The first contact of the upper and lower ends of the relay switch 28 is connected to the power supply terminal 24b side, and the upper second contact 28b is connected to the another of the heater 9. It is connected to the end. The operation by the above electric circuit configuration will be described. First, when 100 V AC is supplied to the supply terminals 24a and 24b, the potential with respect to the input terminal 29b of the connection point of the voltage divider resistors 33 and 34 is low and the constant voltage element 35 does not reach the zener voltage. Do not.

Therefore, the gate potential of the SCR 26 is low, and the OFF 26 is turned off. Therefore, the relay coil 27 is not driven and the common contact 28C of the relay switch 28 is directly connected to the first contact 28a as indicated by the solid line position of FIG. It is a state.

On the other hand, the transistor 36 conducts with the relay coil 27 and the bias resistor 37 interposed therebetween, so that the potentials of the connection points of the resistors 38 and 39 are lowered. Therefore, the gate potential of the triac 40 rises and the triac 40 turns ON. In this way, the first heater 8 and the second heater 9 are parallel to the power supply terminals 24a and 24b, respectively, and AC 100V is supplied to each other.

When AC 200V is supplied next, the connection point of the voltage divider resistors 33 and 34 rises to the potential of the input terminal 29b, and both ends of the constant voltage element 35 reach the zener voltage. Accordingly, the constant voltage element 35 is turned on, so that the gate potential of the SCR 26 rises, and the SCR 26 is turned ON.

As the SCR 26 turns on, the base potential of the transistor 36 goes down and the transistor 36 remains off. Therefore, the potential of the connection point of the resistors 38 and 39 rises and the triac 40 turns off.

이고 제2히터의 저항치는 77

로 된다. 전원전압이 100V의 경우 양 히터의 병렬 저항치는 34

로 되기 때문에 소비전력은 약 290W이 된다.On the other hand, the relay coil 27 is driven so that the contact plate of the relace switch 28 is connected to the second contact 28b as indicated by the dotted line position in FIG. The heater 9 and the heater 8 are connected in series with each other by the above operation. Illustrating the resistance of the heater, the resistance of the first heater 9 is 61

And the resistance of the second heater is 77

It becomes When the supply voltage is 100V, the parallel resistance of both heaters is 34

Since the power consumption is about 290W.

가 되기 때문에 소비전력은 약 290W가 된다. 양쪽의 소비전력은 거의 동일하다.When the power supply voltage is 200V, the series resistance of both heaters is 138

Power consumption is about 290W. The power consumption on both sides is almost the same.

In this embodiment, since the connection state of the first heater 9 and the second heater 8 is automatically switched by the power supply voltage supplied, it is not necessary to check the power supply voltage before using the hair dryer as in the prior art. Therefore, there is no risk of burning the heater by wrong operation, so it can be used with confidence. In addition, since the triac 40 is in the OFF state at the time of 200V connection, an arc is generated between the contacts 28a and 28b at the time of switching the relay switch 28 so that the circuit is not shorted. Therefore, the safety of the relay switch can be achieved. Furthermore, since the trisser signal is first supplied from the voltage dividing lower 33 and 34 to the gate of the SCR 26, the SCR 26 remains in the initial state until the power is turned off. Thus, for example, the relay switch does not lead to a chattering even when used in a 150V voltage region in a part of Colombia. Therefore, it does not lead to problems such as melting of the contact point. Moreover, when two relatively large relays are needed, one relay is sufficient, and the other relay is configured as a triac, which brings about an effect that the storage space of the electrical components is minimized.

Therefore, the present invention can be suitably used for an electric heating device having a small storing interval of parts, such as the curl dryer of this embodiment, which has a smaller outer diameter of the main body and is easier to grip by hand.

Next, a second preferred embodiment of the electric heating apparatus of the present invention will be described with reference to FIGS. 4 and 5.

In this embodiment, the handle is provided at right angles to the blowing direction. It relates to a so-called pistol-type hair dryer.

4 is a cross-sectional view of the hair dryer 51. The hair dryer 51 has a cylindrical case 52, and the discharge port 57 is provided in the front surface of the case 52, and the inlet port 55 is provided in the side surface. The handle 54 is formed in the lower part of the cylindrical case 52. The heater unit 60 is disposed in the discharge port inside the cylindrical case 52. The heater unit 60 has a heater and a temperature riser or limiter. Numeral 58 is a mortar provided in the inlet port 55, and wings 59 are attached to the mortar side. The print engine 63 is fixed to the upper portion of the space 53 in the handle 54. In the lower portion of the space 53, a first relay 64 and a second relay 65 are attached to the pasting plate 64a. A power switch 67 is disposed between the printed board 63 and the pasting board 64. Reference numeral 68 denotes a push button of the power switch 67.

Next, the electric circuit of a hair dryer is demonstrated.

5 shows an electrical circuit diagram of another embodiment. High-voltage voltages of 100-200V or 200-240V are supplied from the supply terminals 70a and 70b of the high-current power supply. From the supply terminals 70a and 70b, the temperature riser or limiter 75 and the temperature fuse 74 or the power switch 67, etc., are sandwiched between the uta 58 and the heater unit. Power is supplied to the heaters 61 and 62 and the drive circuit 78 constituting the 60. Reference numeral 71 denotes a capacitor for preventing noise.

The switch 67 is configured as switches 67a and 67b. The switch 67a turns on and off the power supply, and the switch 67b switches between "weak and weak" of wind and temperature. The switch 67a is closed by pushing the pushbutton 68 once. The switch 67b is closed by pressing again. When the switch 67a is ON or the switch 67b is OFF, the rectifying diode 72 and the resistor 73 are inserted into the circuit to be half-wave rectified and supplied to the heater. The effective value of the voltage is reduced. Thus, the wind temperature becomes "about."

When the switches 67a and 67b are ON together, the rectifier diode 72 and the resistor 73 are short-circuited, so that the AC voltage is applied to the heater as it is, so that the effective value of the voltage supplied to the heater is reduced. none. Thus the wind temperature becomes "river". The dotted line 79 surrounds the mouta 58 and the mouta driving circuit. The motor drive circuit is formed as a rectified bridge diode (BRIDGE DIODE) 76 which is connected in parallel with a part of the first heater 61 and supplies a DC output to the motor 58. The dotted line 77 surrounds the half-wave rectifier circuit formed as the diode 77b and the resistor 77a.

Direct current is supplied to the drive circuit by the diode 77b. The dotted line 78 surrounds the drive circuit as drive means. A constant voltage diode 79c is connected between the step-down resistor 79a from the input terminal 80a of the drive circuit. A two-terminal circuit formed as a relay coil and an SCR 81 are serially connected to both ends of the constant voltage diode 79c. In the two-terminal circuit, the relay coil 66 and the relay switch 65b connected to each other in series with the relay coil 65 are connected in parallel. The relay switch 65b is interlocked with the relay coil 64 so that the relay switch 65b is turned ON when the relay coil 65 is not driven. By the above connection, the SCR 81 operates at a constant voltage. 79b is a smoothing capacitor. The divided terminals 78a and 78b connected in series with each other are connected to the input terminals 80a and 80b of the drive circuit 78. The connection points of the voltage divider resistors 78a and 78b are connected to the gate of the SCR 81 with the constant voltage element 78c attached thereto. The voltage dividing ratio of the voltage dividing resistors 78a and 78b is set so that the constant voltage element 78c reaches the zener voltage when the power supply voltage becomes 150V or more.

One end of the first heater 61 is connected to the power supply terminal 70b side, and the other end thereof is connected to the power supply terminal 70a side with the upper and rear relay switch 65c serving as an open / close switch interposed therebetween. The relay switch 65c is interlocked with the relay coil 65 so that the relay switch 65c is turned off during the non-driving time of the relay coil 65. One end of the second heater 62 is connected to the power supply terminal 70a, and the other end is connected to the common terminal 66c of the retrace switch 66. The first contact 66a of the relay switch 66 is connected to the power supply terminal 70b side, and the second contact 66b is connected to the other end of the heater 61. When the relay coil 64 is not driven, the common contact 66c is closed to the first contact 66a side, and when the relay coil 64 is driven, the common contact 66c is closed to the second contact 66b side. The operation by the above electric circuit configuration will be described.

First, in the state where AC 100V is supplied to the power supply terminals 70a and 70b, the potential of the connection point of the divided resistors 78a and 78b is low, so that the constant voltage element 78c does not reach the zener voltage. Therefore, the gate potential of the SCR 81 is low and turned off. Therefore, the relay coil 65 is not driven and the relay switch 65c of the normal closing is closed.

On the other hand, since the relace switch 65b is open, the relay coil 64 is not driven, and the relace switch 66 is connected to the first contact point 66a of the upper and lower closures. In this way, the first heater 61 and the second heater 62 are connected in parallel to each other and AC 100V is supplied. Next, when AC 200V is supplied, the electric potential of the connection point of the voltage divider resistors 78a and 78b rises and conducts when the constant voltage element 78c reaches the zener voltage. Therefore, the gate potential of the SCR 81 rises and the SCR 81 is turned ON.

In response to the SCR 81 being turned on, the relay coil 65 is driven to close the relay switch 65b, and the relay switch 65c is opened. After the relace switch 65b is closed, the relay coil 64 is driven to connect the relace switch 66 to the second contact 66b. Therefore, the first heater 61 and the second heater 62 are connected in series with each other.

In this embodiment, since the connection state of the first heater and the second heater is automatically switched by the power supply voltage supplied, it is not necessary to check the power supply voltage before using the hair dryer as in the prior art. Therefore, there is no risk of burning the heater by wrong operation and it can be used with confidence. In addition, since the relace switch 66 does not operate unless the relace switch 65c is completely opened, the power may be disconnected without generating an arc between the contacts 78a and 78b of the relace switch 66. none.

Furthermore, since the trigger signal is supplied from the voltage divider resistors 78a and 78b to the gate of the SCR 81 once, the SCR 81 continues to maintain its initial state until the power is turned off. Thus, for example, the relay switch does not cause chattering when used in a 150V voltage region in parts of Colombia. Therefore, it does not lead to problems such as melting of the contact point.

Next, a case in which a protective resistor is added to the electric circuits of the first and second preferred embodiments will be described with reference to FIGS. 6 and 7.

6 is a circuit in which a protection resistor 44 is inserted between the first contact 28a of the relace switch 28 and the power supply terminal 24b in the electrical circuit (see FIG. 3) of the first embodiment. Is displayed. Assume that the hair dryer was accidentally dropped while using the power supply voltage 100V.

The contact plate of the relace switch 28 vibrates to move between the contacts 28a and 28b. For this reason, the contacts 28a and 28b are short-circuited by an arc across a contact plate. Without the protection resistor 44, a large current flows instantaneously (over a half cycle period of exchange over several msec), and the current flowing through the protection resistor 44 is suppressed.

이고, 제2히터의 저항치가 77

인데 대하여 3

정도의 것에 불과한 것이다. 상기의 보호저항(44)은 풍로상에 설치되여 있으므로 발생하는 열을 유효하게 이용하는 관점에서 바람직한 것이다. 이를테면 보호저항(44)은 제1도 그 점선에서 표시햐는 바와 같이 십자 모양으로 조합시킨 절연기판(7)에 장치되여 있다.To illustrate the resistance of the protection resistor 44, the resistance of the first heater 9 is 61

And the resistance of the second heater is 77

About 3

It is only about. Since the above-mentioned protective resistor 44 is provided on the air path, it is preferable from the viewpoint of effectively utilizing the generated heat. For example, the protective resistor 44 is mounted on the insulating substrate 7 which is combined in a cross shape as indicated by the dotted line in FIG.

FIG. 7 shows the protection resistor 83 inserted between the relay contact 66b and the heater 61 in the electrical circuit (see FIG. 5) of the second embodiment, and the relay switch 65c and the heater ( The circuit in which the protection resistor 84 is inserted between 61 is shown.

As in the case of FIG. 6, the protection resistors 83 and 84 can be prevented from being shorted by the arc current generated by the vibration of the contact plate of the retrace switch 66.

It is preferable that the protective resistors 83 and 84 effectively utilize heat generated by being disposed on the air path as in the above-described embodiment. In addition, the insertion position of a protection resistor is not limited to the above-mentioned embodiment, In FIG. 6, between the power supply terminal 24a-triac 40-relay contact 28b, or the relay contact 28a. The power supply terminal 70a--relay switch 65c--relay contact 66b may be inserted in series at any of the positions between the power supply terminals 24b. It may be inserted in series at either of the positions between the relay contact 66a and the power supply terminal 70b.

As mentioned above, although this invention was demonstrated in detail based on an Example, referring an accompanying drawing, it is not limited to the above-mentioned silencing example, Comprising: Various changes are possible for it unless it isolate | separates from the range and mind of this invention. It should be understood.

Claims (2)

As the pressure is detected, each switch is driven so that the first and second heaters 8 and 9 are connected to each other in series or in parallel. An electric heating device comprising a transistor (36) as a switching element and a triac (40) as an open / close switch. 2. The driving circuit as set forth in claim 1, further comprising a driving circuit (78) for driving each switch as a voltage is detected so that the first heater (61) and the second heater (62) are connected in series or in parallel. The furnace (78) is composed of an SCR (81) as a switch device, a relay coil (64) (65) as a switching switch, and a relay switch (65b).

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