AU2016394592A1

AU2016394592A1 - Household electrical appliance and air conditioner

Info

Publication number: AU2016394592A1
Application number: AU2016394592A
Authority: AU
Inventors: Yuhei Shimada
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2016-02-22
Filing date: 2016-02-22
Publication date: 2018-07-12
Anticipated expiration: 2036-02-22
Also published as: AU2016394592B2; JPWO2017145247A1; WO2017145247A1; JP6466023B2

Abstract

A household electrical appliance 100-1 is characterized by being provided with: a low-voltage circuit 8 that outputs a low voltage; a low-voltage terminal 5; a high-voltage terminal 4; and a switch 6, which is disposed between the low-voltage circuit 8 and the low-voltage terminal 5, and which brings the low-voltage circuit 8 and the low-voltage terminal 5 into a connected state when an alternating current voltage is applied to the high-voltage terminal 4, and which brings the low-voltage circuit 8 and the low-voltage terminal 5 into a non-contact state when the alternating current voltage is not applied to the high-voltage terminal 4. The household electrical appliance is also characterized in that a component can be prevented from breaking even in the cases where a high voltage is applied to the low-voltage terminal 5.

Description

DESCRIPTION HOUSEHOLD ELECTRICAL APPLIANCE AND AIR CONDITIONER Field [0001] The present invention relates to a household electrical appliance and an air conditioner that each have a function that protects them against the application, due to erroneous wiring, of a high voltage to a low-voltage terminal.

Background [0002] Conventional air conditioners include an erroneous-wiring protection unit to provide protection in the event that, due to erroneous wiring, high-voltage power is applied to a low-voltage control circuit. Because a general erroneous-wiring protection unit is configured under the assumption that a circuit is protected when a high voltage is detected, the unit has a complicated circuit configuration and involves an increase in the number of components, and thus there is a concern that costs are increased. One view is to use a protection component, typically a fuse, which requires replacement when a circuit is damaged by the application of a high voltage. However, because using such a protection involves replacing the component and conducting repairs, labor is required and expense are incurred.

[0003] To solve the problems, in a conventional technique described in Patent Literature 1, a switch is provided in a portion of a power-supply line and in a portion of a signal transmission line that connect the indoor unit and the outdoor unit of an air conditioner.

The switch protects the circuit board by bringing in an open state when there is erroneous wiring. Further, according to a conventional technique described in Patent Literature 2, in an air conditioner, a switch is provided in a three-phase power-supply control circuit to which three-phase high-voltage power at 200 V is input and in a power-supply control circuit to which single-phase low-voltage power at 100 V is input. The switch protects the circuit board by bringing in an open state when there is erroneous wiring.

[0004] As described above, with the protection against erroneous wiring described in Patent Literatures 1 and 2, it is assumed that protection is introduced to the low-voltage control circuit of an air conditioner. Further, for all circuits to which a high voltage is applied when erroneous wiring occurs, measures are taken to prevent the low-voltage control circuit being damaged; and measures are also taken in order for the low-voltage control circuit to operate well at the low voltage for which it was originally designed.

Citation List Patent Literatures [0005] Patent Literature 1: Japanese Patent Application Laid-open No. 2007-113856

Patent Literature 2: Japanese Patent Application Laid-open No. S63-116318

Summary

Technical Problem [0006] With the conventional technique of Patent Literature 1, it assumed there is only erroneous wiring between the indoor unit and the outdoor unit in the air conditioner and there is no consideration of measures against erroneous wiring in any connection with an external device other than the indoor unit.

[0007] Further, with the conventional technique of Patent Literature 2, as is the case with the technique of Patent Literature 1, there is no consideration of measures against erroneous wiring making a connection with an external device other than the indoor unit. With the conventional technique of Patent Literature 2, it is assumed that there is only erroneous wiring between a power-supply line of three-phase high-voltage power at 200 V and a power-supply line of single-phase low-voltage power at 100 V, and there is also no consideration of the application of a single-phase high-voltage power at 200 V to a single-phase low-voltage control circuit at 100 V.

[0008] The objective, in view of the above problems, of the present invention is to provide a household electrical appliance that can prevent damage to components even when a high voltage is applied to a low-voltage terminal.

Solution to Problem [0009] In order to solve the problem above and achieve the objective, the household electrical appliance of the present invention includes: a low-voltage circuit to output a low voltage; a low-voltage terminal; a high-voltage terminal; and a switch, provided between the low-voltage circuit and the low-voltage terminal, to bring the low-voltage circuit and the low-voltage terminal into a connected state while an alternating-current voltage is being applied to the high-voltage terminal and to bring the low-voltage circuit and the low-voltage terminal into an unconnected state while the alternating-current voltage is not being applied to the high-voltage terminal.

Advantageous Effects of Invention [0010] According to the household electrical appliance of the present invention, there is an effect where it is possible to prevent damage to components even when a high voltage is applied to a low-voltage terminal.

Brief Description of Drawings [0011] FIG. 1 is a configuration diagram of a circuit included in a household electrical appliance according to a first embodiment of the present invention. FIG. 2 is a configuration diagram of the power-supply circuit illustrated in FIG. 1. FIG. 3 is an explanatory diagram of an operation when there is erroneous wiring in the household electrical appliance according to the first embodiment of the present invention . FIG. 4 is a configuration diagram of a circuit included in an air conditioner according to a second embodiment of the present invention. FIG. 5 is a configuration diagram of the power-supply circuit mounted on the main circuit board illustrated in FIG. 4. FIG. 6 is an explanatory diagram of an operation when there is erroneous wiring in the air conditioner according to the second embodiment of the present invention.

Description of Embodiments [0012] A household electrical appliance and an air conditioner according to embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The present invention is not limited to the embodiments.

[0013] First embodiment FIG. 1 is a configuration diagram of a circuit included in a household electrical appliance according to a first embodiment of the present invention. A household electrical appliance 100-1 according to the first embodiment includes a main circuit board 3, to which a single-phase commercial power supply 1 and an external device 2 are connected. Examples of the household electrical appliance 100-1 are a refrigerator, an air conditioner, and a television. In FIG. 1, illustrations of constituent elements other than the main circuit board 3 included in the household electrical appliance 100-1 are omitted. In a case where the household electrical appliance 100-1 is a refrigerator, the constituent elements other than the main circuit board 3 are components such as a housing constituting the exterior of the refrigerator, a refrigeration cycle mechanism provided in the housing, an electric motor, an electric-motor driving device, and a blower fan.

[0014] The main circuit board 3 includes a low-voltage circuit 8 that outputs a low voltage; a low-voltage terminal 5 to which a low voltage is applied; a high-voltage terminal 4 to which an alternating-current voltage is applied that is higher than the low voltage and that is the voltage of the single-phase commercial power supply 1; a power-supply circuit 7; and a switch 6. Although the high-voltage terminal 4 and the low-voltage terminal 5 are provided on the main circuit board 3 in the present embodiment, the high-voltage terminal 4 and the low-voltage terminal 5 can be provided at locations other than the main circuit board 3. For example, in a case where the household electrical appliance 100-1 is an air conditioner, when the main circuit board 3 is arranged in an electrical-component box arranged in an outdoor unit of the air conditioner, the high-voltage terminal 4 and the low-voltage terminal 5 can be fixed to the housing of the electrical-component box. In this case, a wire connecting the main circuit board 3 and the high-voltage terminal 4 to each other and a wire connecting the main circuit board 3 and the low-voltage terminal 5 to each other are provided at the high-voltage terminal 4 and the low-voltage terminal 5 that are fixed to the housing.

[0015] In FIG. 1, a wire la connected to the commercial power supply 1 is connected to the high-voltage terminal 4; and a wire 2a connected to the external device 2 arranged outside the household electrical appliance 100-1 is connected to the low-voltage terminal 5. In the present embodiment, a state where the wires la and 2a are connected as illustrated in FIG. 1 is referred to as "normal wiring". In contrast, a state where the wire la is connected to the low-voltage terminal 5 is referred to as "erroneous wiring".

[0016] The switch 6 is an erroneous-wiring protection unit and is provided to prevent damage to a circuit component on the main circuit board 3 including the low-voltage circuit 8 when the wire la is connected to the low-voltage terminal 5 due to erroneous wiring. The switch 6 is arranged between the low-voltage circuit 8 and the low-voltage terminal 5. It brings the low-voltage circuit 8 and the low-voltage terminal 5 into a connected state while the alternating-current voltage of the commercial power supply 1 is being applied to the high-voltage terminal 4; and it brings the low-voltage circuit 8 and the low-voltage terminal 5 into an unconnected state while the alternating-current voltage of the commercial power supply 1 is not being applied to the high-voltage terminal 4.

[0017] The switch 6 can have any configuration as long as it is a switch circuit driven by a voltage output from the power-supply circuit 7. Examples of the switch 6 include an electromagnetic relay, a Metal Oxide Semiconductor Field Effect Transistor (MOSFET), and a photo-coupler. In a case where the switch 6 is an electromagnetic relay, the electromagnetic relay includes a coil and a plunger. While a voltage is not being output from the power-supply circuit 7, the coil is not excited and the plunger is not driven, and therefore the low-voltage circuit 8 is not connected to the low-voltage terminal 5. While a voltage of a certain value or higher is being output from the power-supply circuit 7, the coil is excited and therefore the plunger is driven, and therefore the low-voltage circuit 8 is connected to the low-voltage terminal 5.

[0018] FIG. 2 is a configuration diagram of the power-supply circuit illustrated in FIG. 1. The power-supply circuit 7 includes a noise filter 71, a diode bridge 72, a reactor 73, an Insulated Gate Bipolar Transistor (IGBT) 74, a shunt resistor 75, a rectifier diode 76, an electrolytic capacitor 77, an inverter circuit 78, and a Direct Current-Direct Current (DCDC) circuit 79.

[0019] The input side of the noise filter 71 is connected to the high-voltage terminal 4. The noise filter 71 is provided to prevent a conductive noise generated in the power-supply circuit 7 from being propagated outside the power-supply circuit 7 via the wire la and thus influencing peripheral devices.

[0020] The diode bridge 72 is a full-wave rectifier circuit configured by combining four diodes. The configuration of the diode bridge 72 is not limited thereto and it can be configured by combining MOSFETs that are unidirectional conducting elements.

[0021] One end of the reactor 73, which is arranged in a positive-side direct-current bus P, is connected to the diode bridge 72; and the other end of the reactor 73 is connected to a connection point between the anode of the rectifier diode 76 and the IGBT 74.

[0022] The collector of the IGBT 74 is connected to the anode of the rectifier diode 76, and the emitter of the IGBT 74 is connected to one end of the shunt resistor 75. A control circuit (not illustrated) is connected to the gate of the IGBT 74. The other end of the shunt resistor 75 is connected to a negative-side direct-current bus N. One end of the electrolytic capacitor 77 is connected to the positive-side direct-current bus P, and the other end of the electrolytic capacitor 77 is connected to the negative-side direct-current bus N.

[0023] The inverter circuit 78 includes six switching elements (not illustrated). Three of the six switching elements are arranged on the side close to the positive-side direct-current bus P and constitute an upper-arm switching-element group; and three of the six switching elements are arranged on the side close to the negative-side direct-current bus N and constitute a lower-arm switching-element group. An alternating-current electric motor (not illustrated) is connected to a connection point between the upper-arm switching-element group and the lower-arm switching-element group.

[0024] The six switching elements constituting the inverter circuit 78 are semiconductor switches such as a Dual Inline Package Intelligent Power Module (DIPIPM), an Intelligent Power Module (IPM), an IGBT, a MOSFET, an Insulated Gate Controlled Thyristor (IGCT), or a Field Effect Transistor (FET).

[0025] The DCDC circuit 79 converts a direct-current voltage applied to a direct-current bus to a voltage of a desired value and outputs that voltage to the switch 6 and to a microcomputer 81 in the low-voltage circuit 8. The microcomputer 81 in the low-voltage circuit 8 generates, by using direct-current power supplied from the DCDC circuit 79, power for driving the external device 2 and outputs the generated power. Although FIG. 2 illustrates a configuration example in which the switch 6 is caused to operate by power supplied from the DCDC circuit 79, it is permissible that alternating-current power is supplied from the noise filter 71 to the switch 6 in order to cause the switch 6 to operate when the commercial power supply 1 is connected to the high-voltage terminal 4.

[0026] Next, an operation in a case of normal wiring is described.

[0027] In FIG. 1, in a case where the wire la of the commercial power supply 1 is connected to the high-voltage terminal 4 and the wire 2a of the external device 2 is connected to the low-voltage terminal 5, which establishes a normal wiring state, the voltage of the commercial power supply 1 is applied to the power-supply circuit 7 via the high-voltage terminal 4.

[0028] An alternating-current voltage applied to the power-supply circuit 7 is subjected to full-wave rectification by the diode bridge 72. By an on-off operation of the IGBT 74 repeated a plurality of times, a direct-current voltage smoothed by the electrolytic capacitor 77 is applied to the inverter circuit 78 and the DCDC circuit 79. The direct-current voltage applied to the inverter circuit 78 is converted to an alternating-current voltage by a switching operation of the switching element of the inverter circuit 78; and the alternating-current voltage is supplied to a load. Also, the direct-current voltage applied to the DCDC circuit 79 is stepped down to a direct-current voltage of a desired value by an operation of the DCDC circuit 79, and the resultant direct-current voltage is applied to the microcomputer 81 and the switch 6. Therefore, the switch 6 enters a closed state, and therefore the low-voltage terminal 5 and the low-voltage circuit 8 are brought into a connected state. As a result, the low-voltage circuit 8 and the external device 2 are connected to each other; and the main circuit board 3 and the external device 2 operate normally.

[0029] Next, an operation in a case of erroneous wiring is described.

[0030] FIG. 3 is an explanatory diagram of an operation when there is erroneous wiring in the household electrical appliance according to the first embodiment of the present invention. When the wire 2a of the external device 2 is connected to the high-voltage terminal 4 and the wire la of the commercial power supply 1 is connected to the low-voltage terminal 5, which causes erroneous wiring as illustrated in FIG. 3, power is not supplied to the power-supply circuit 7. In this case, no direct-current voltage is applied to a direct-current bus or to the DCDC circuit 79. Therefore, no direct-current voltage is applied to the microcomputer 81 or to the switch 6, and therefore the switch 6 enters an open state; and the low-voltage terminal 5 and the low-voltage circuit 8 are brought into an unconnected state. As a result, it is possible to prevent application of the high voltage of the commercial power supply 1 to the low-voltage circuit 8 via the low-voltage terminal 5. In FIG. 3, the wire 2a of the external device 2 is connected to the high-voltage terminal 4. However, also in a case where the wire 2a of the external device 2 is connected to the low-voltage terminal 5, the switch 6 enters an open state. Therefore, also in this case, it is possible to prevent application of the voltage of the commercial power supply 1 to the low-voltage circuit 8 via the low-voltage terminal 5.

[0031] As described above, the household electrical appliance 100-1 according to the present embodiment is configured in such a manner that the switch 6 brings the low-voltage terminal 5 and the low-voltage circuit 8 into an unconnected state when there is erroneous wiring. Therefore, even when a high voltage is applied to the low-voltage terminal 5, it is possible to prevent components from damage. Further, with the household electrical appliance 100-1, the only component required to be added for protection against erroneous wiring is the switch 6. Therefore, the circuit configuration is simple and the number of added components is low. Consequently, it is possible to suppress an increase in cost for protection against erroneous wiring and to prevent the reliability from lowering. Further, a protection component, typically a fuse, that requires replacement when there is erroneous wiring, is not required. Therefore, it is possible to reduce the time and cost required to replace a component and make repairs.

[0032] Second embodiment FIG. 4 is a configuration diagram of a circuit included in an air conditioner according to a second embodiment of the present invention. Whereas the first embodiment describes the household electrical appliance 100-1 as having an erroneous-wiring protection function with the assumption that there are connections to various external devices 2, the second embodiment describes an air conditioner 100-2 having an erroneous-wiring protection function with the assumption that there is a connection with a demand signal transmitter, which is referred to as a "Demand Response Enabling Device (DRED)".

[0033] The DRED is a signal transmitter for executing, in an air conditioner, demand management control in response to a demand request transmitted from a power company. The background technology of the DRED is described below. In recent years, measures against global warming have been pushed forward globally. As part of those measures, energy saving is required to each household electrical appliance. Under such circumstances, for an air conditioner, the need is increasing for power-usage demand management of power usage in accordance with the power demand as the maximum demand power increases. There is a need to perform demand management on commercial air conditioners for business use used in buildings or large structures and also on domestic air conditioners used in homes. In Australia, in particular, demand management in accordance with the Australian standard [AS4755] has been implemented. In the Australian standard [AS4755], it is specified that a device referred to as a "DRED" and an air conditioner are connected to each other. An operation of a demand signal transmitter is described here. First, when a request for limiting power usage, i.e., a demand request, is input to the DRED from a remote operating device on the power supplier side, the DRED transmits a signal that limits the power usage and indicates the level of the limit request, i.e., a demand signal sent to the air conditioner. Upon receiving the demand signal, the air conditioner limits its power usage in accordance with the limit request level. Therefore, it is possible to alleviate a buildup of power demand.

[0034] FIG. 4 illustrates the main circuit board 3 and a sub-circuit board 10 included in an outdoor unit of the air conditioner 100-2 according to the second embodiment, and it also illustrates a DRED 20 connected to the sub-circuit board 10. Although the configuration of the main circuit board 3 is identical to that in the first embodiment, the sub-circuit board 10 has a function as a circuit that receives a signal from the DRED 20. Hereinafter, identical elements to those in the first embodiment are denoted by like reference numbers, and the descriptions thereof are omitted. Only different elements are described herein.

[0035] The sub-circuit board 10 includes a first low-voltage terminal 12, to which a low voltage for the subcircuit board 10 is applied via a wire 12s; and a high-voltage terminal 14 connected to the high-voltage terminal 4 of the main circuit board 3 via a wire 14a, to which a voltage of the single-phase commercial power supply 1 is applied.

[0036] Further, the sub-circuit board 10 includes a second low-voltage terminal 16 for a sub-circuit board 10 and a switch 15. A low-voltage circuit 11, a power-supply circuit 13, and the DRED 20 are connected to the second low-voltage terminal 16. The second low-voltage terminal 16 supplies low-voltage power output from the low-voltage circuit 11 to the DRED 20.

[0037] In FIG. 4, the wire 12a connected to the first low-voltage terminal 12 is connected to the low-voltage terminal 5; the wire la connected to the commercial power supply 1 is connected to the high-voltage terminal 4; the wire 14a connected to the high-voltage terminal 14 is connected to the high-voltage terminal 4; and a wire 20a connected to the DRED 20 is connected to the second low-voltage terminal 16. In the present embodiment, a state where the wires la, 14a, and 12a are connected as illustrated in FIG. 4 is referred to as "normal wiring".

In contrast, a state where the wire la is connected to the low-voltage terminal 5 is referred to as "erroneous wiring".

[0038] The switch 15 is an erroneous-wiring protection unit provided on the sub-circuit board 10; and it is provided to prevent, when the wire la is connected to the low-voltage terminal 5 due to erroneous wiring, damage to circuit components on the main circuit board 3 including the low-voltage circuit 8 and damage to the DRED 20 connected to the sub-circuit board 10.

[0039] The switch 15 is arranged between the first low-voltage terminal 12 and the second low-voltage terminal 16. The switch 15 brings the first low-voltage terminal 12 and the second low-voltage terminal 16 into a connected state while an alternating-current voltage of the commercial power supply 1 is being applied to the high-voltage terminal 14; and it brings the first low-voltage terminal 12 and the second low-voltage terminal 16 into an unconnected state while an alternating-current voltage from the commercial power supply 1 is not being applied to the high-voltage terminal 14.

[0040] The switch 15 can have any configuration as long as it is a switch circuit driven by an alternating-current voltage applied to the power-supply circuit 13 via the high-voltage terminal 14. Examples of the switch 15 include an electromagnetic relay, a MOSFET, and a photocoupler. In a case where the switch 15 is an electromagnetic relay, the electromagnetic relay includes a coil and a plunger. While a voltage is not being applied to the high-voltage terminal 14, the coil is not excited and the plunger is not driven, and therefore the first low-voltage terminal 12 is not connected to the second low-voltage terminal 16. While a voltage of a certain value or higher is being applied to the high-voltage terminal 14, the coil is excited and drives the plunger, and therefore the first low-voltage terminal 12 is connected to the second low-voltage terminal 16. This means that, when in a state of normal wiring, the single-phase commercial power supply 1 is connected to the high-voltage terminal 4 of the main circuit board 3, and it is also connected to the high-voltage terminal 14 of the sub-circuit board 10. Also, when in a state of normal wiring, the DRED 20, the wire 20a, the second low-voltage terminal 16, the first low-voltage terminal 12, the wire 12a, and the low-voltage terminal 5 are connected to one another.

[0041] FIG. 5 is a configuration diagram of a power-supply circuit mounted on the main circuit board illustrated in FIG. 4. The power-supply circuit 7 illustrated in FIG. 5 has an identical circuit to that in the first embodiment. The switch 15, the power-supply circuit 13, and the low-voltage circuit 11 are mounted on the sub-circuit board 10. Power from the commercial power supply 1 is supplied to the switch 6 of the main circuit board 3 via the circuit in the power-supply circuit 7.

Power from the commercial power supply 1 is supplied to the switch 15 of the sub-circuit board 10 but not via the circuit in the power-supply circuit 7.

[0042] Next, an operation in a case of normal wiring is described.

[0043] In FIG. 4, in a case where the wire la of the commercial power supply 1 is connected to the high-voltage terminal 4 and the wire 12a is connected to the low-voltage terminal 5 to establish a normal wiring state, a voltage of the commercial power supply 1 is applied to the power-supply circuit 7 via the high-voltage terminal 4 and is also applied to the switch 15.

[0044] An alternating-current voltage applied to the power-supply circuit 7 is subjected to full-wave rectification by the diode bridge 72. By repeatedly forming an on-off operation of the IGBT 74 a plurality of times, a direct-current voltage smoothed by the electrolytic capacitor 77 is applied to the inverter circuit 78 and the DCDC circuit 79. The direct-current voltage applied to the inverter circuit 78 is converted to an alternating-current voltage by the switching operation of the switching element of the inverter circuit 78, and the alternating-current voltage is supplied to a load 50. Examples of the load 50 are a three-phase synchronous alternating-current motor and a three-phase induction alternating-current motor.

[0045] The direct-current voltage applied to the DCDC circuit 79 is stepped down to a direct-current voltage of a desired value by an operation of the DCDC circuit 79, and the resultant direct-current voltage is applied to the microcomputer 81 and the switch 6. Therefore, the switch 6 enters a closed state, and therefore the low-voltage terminal 5 and the low-voltage circuit 8 are brought into a connected state. Further, the switch 15 of the sub-circuit board 10 enters a closed state due to the voltage applied via the high-voltage terminal 14, and therefore the low-voltage circuit 11 and the second low-voltage terminal 16 are brought into a connected state. As a result, the low-voltage circuit 8 and the DRED 20 are connected to each other; the power-supply circuit 7 and the sub-circuit board 10 operate normally; and communication with the DRED 20 is performed normally.

[0046] Next, an operation in a case of erroneous wiring is described.

[0047] FIG. 6 is an explanatory diagram of an operation when there is erroneous wiring in the air conditioner according to the second embodiment of the present invention.

When the wire 12a is connected to the high-voltage terminal 4 and the wire la of the commercial power supply 1 is connected to the low-voltage terminal 5, which creates erroneous wiring as illustrated in FIG. 6, power is not supplied to the power-supply circuit 7 of the main circuit board 3. Therefore, any direct-current voltage is not applied to a direct-current bus or to the DCDC circuit 79. Therefore, any direct-current voltage is not applied to the microcomputer 81 or to the switch 6, and thus the switch 6 enters an open state, and the low-voltage terminal 5 and the low-voltage circuit 8 are brought into an unconnected state. As a result, it is possible to prevent application of a high voltage of the commercial power supply 1 to the low-voltage circuit 8 via the low-voltage terminal 5.

[0048] Further, in the case of erroneous wiring as illustrated in FIG. 6, no voltage is applied to the switch 15 of the sub-circuit board 10, the switch 15 enters an open state, and the first low-voltage terminal 12 and the second low-voltage terminal 16 are brought into an unconnected state. As a result, it is possible to prevent application of a high voltage of the commercial power supply 1 to the DRED 20 via the second low-voltage terminal 16. In FIG. 6, the DRED 20 is connected to the high-voltage terminal 4 via the sub-circuit board 10, but, as is also in the case where the wire 12a of the sub-circuit board 10 is connected to the low-voltage terminal 5, the switch 15 is in an open state. Therefore, also in this case, it is possible to prevent application of the voltage of the commercial power supply 1 to the DRED 20.

[0049] As described above, the air conditioner 100-2 according to the present embodiment is configured in such a manner that, when there is erroneous wiring, the switch 6 brings the low-voltage terminal 5 and the low-voltage circuit 8 into an unconnected state; and the switch 15 brings the first low-voltage terminal 12 and the second low-voltage terminal 16 into an unconnected state. Therefore, even when a high voltage is applied to the low-voltage terminal 5, it is possible to prevent damage to the circuit components of the main circuit board 3 as in the first embodiment, and it is also possible to prevent damage to the DRED 20 connected to the second low-voltage terminal 16. Further, with the air conditioner 100-2 of the second embodiment, the only components required to be added for protection against erroneous wiring are the switches 6 and 15. Therefore, the circuit configuration is simple and the number of added components is small. Accordingly, it is possible to suppress an increase in cost for protection against erroneous wiring and to suppress lowering of reliability. Further, a protection component, typically a fuse which requires replacement when there is erroneous wiring, is not required. Therefore, it is possible to reduce the time and cost required to replace a component and make repairs.

[0050] The first and second embodiments describe example configurations of the household electrical appliance 100-1 and the air conditioner 100-2 that each operate with the commercial power supply 1, each of which is a single-phase alternating-current power supply. However, the household electrical appliance 100-1 and the air conditioner 100-2 can each be configured to operate with a three-phase alternating-current power supply. Also in this case, identical effects can be obtained in the first and second embodiments .

[0051] The first embodiment describes an example configuration in which the switch 6 is caused to operate by using the output voltage of the DCDC circuit 79, and the second embodiment describes an example configuration in which the switch 6 is caused to operate by using the output voltage of the DCDC circuit 79 and the switch 15 is caused to operate by using a voltage of the commercial power supply 1. However, each of the switches 6 and 15 can be configured to operate due to a voltage output from the microcomputer 81. By controlling the timing of the output of the voltage from the microcomputer 81, the operation timing of each of the switches 6 and 15 can be set to an arbitrary timing. Therefore, it is possible to control, in an arbitrary manner, the timing of the connection with the external device 2 according to the first embodiment or the DRED 20 according to the second embodiment.

[0052] The configurations described in the above embodiments are only examples of the present invention.

The configurations can be combined with other well-known techniques, and a part of each configuration can be omitted or modified without departing from the scope of the present invention .

Reference Signs List [0053] 1 commercial power supply, la, 2a, 12a, 14a, 20a wire, 2 external device, 3 main circuit board, 4, 14 high-voltage terminal, 5 low-voltage terminal, 6, 15 switch, 7, 13 power-supply circuit, 8, 11 low-voltage circuit, 10 sub-circuit board, 12 first low-voltage terminal, 16 second low-voltage terminal, 50 load, 71 noise filter, 72 diode bridge, 73 reactor, 74 IGBT, 75 shunt resistor, 76 rectifier diode, 77 electrolytic capacitor, 78 inverter circuit, 79 DCDC circuit, 81 microcomputer, 100-1 household electrical appliance, 100-2 air conditioner.

Claims

1. A household electrical appliance comprising: a low-voltage circuit to output a low voltage; a low-voltage terminal; a high-voltage terminal; and a switch, provided between the low-voltage circuit and the low-voltage terminal, to bring the low-voltage circuit and the low-voltage terminal into a connected state while an alternating-current voltage is being applied to the high-voltage terminal and to bring the low-voltage circuit and the low-voltage terminal into an unconnected state while the alternating-current voltage is not being applied to the high-voltage terminal.

2. The household electrical appliance according to claim 1, wherein the alternating-current voltage is a three-phase alternating-current voltage.

3. The household electrical appliance according to claim 1 or 2, wherein the switch is caused to operate by an output voltage of a microcomputer mounted in the household electrical appliance.

4. An air conditioner comprising: a low-voltage circuit to output a low voltage; a low-voltage terminal; a high-voltage terminal; a switch, provided between the low-voltage circuit and the low-voltage terminal, to bring the low-voltage circuit and the low-voltage terminal into a connected state while an alternating-current voltage is being applied to the high-voltage terminal and to bring the low-voltage circuit and the low-voltage terminal into an unconnected state while the alternating-current voltage is not being applied to the high-voltage terminal; a first low-voltage terminal for a sub-circuit board, which is connected to the low-voltage terminal; a second low-voltage terminal for the sub-circuit board, which is connected to a demand signal transmitter; a high-voltage terminal for the sub-circuit board, which is connected to the high-voltage terminal; and a switch for the sub-circuit board, which is provided between the first low-voltage terminal and the second low-voltage terminal, to bring the first low-voltage terminal and the second low-voltage terminal into a connected state while the alternating-current voltage is being applied to the high-voltage terminal for the sub-circuit board and to bring the first low-voltage terminal and the second low-voltage terminal into an unconnected state while the alternating-current voltage is not being applied to the high-voltage terminal for the sub-circuit board.

5. The air conditioner according to claim 4, wherein the alternating-current voltage is a three-phase alternating-current voltage.

6. The air conditioner according to claim 4 or 5, wherein the switch and the switch for the sub-circuit board are caused to operate by an output voltage of a microcomputer mounted in the air conditioner.