Improvements relating to power supplies for home appliances with ALCI functions

Abstract

An appliance leakage circuit interrupter (ALCI) (or residual current device (RCD)) includes a self-test (automonitoring) function. The device has a leakage current detection circuit module 86 which ou

Description

Home appliances, and particularly haircare appliances, are generally used to treat or style hair, and some haircare appliances may treat or style hair using airflow along with heat. Such haircare appliances are typically held by a user and moved relative to the hair to obtain desired treatment or styling. Other appliances, such as space heaters and hand-dryers, may also output a heated airflow. For safety purposes, such appliances may be equipped with power cut-out systems which are configured to cut power to the appliance in response to detecting potentially unsafe operating conditions. Such cut-out systems may be referred to as circuit breakers, or residual current devices. Other terms of art may also be appropriate. SUMMARY OF INVENTION A first aspect the invention provides an appliance leakage circuit interrupter (ALCI) device having a self-test function, which are also known as an automonitoring function. The ALCI device comprises a leakage current detection circuit module which is configured to: receive a phase current signal from a current sensor; determine the presence of a leakage current based on the phase current signal; output a solenoid trigger signal in the event that leakage current is detected; and, output a leakage test signal, that is indicative either of an active automonitoring testing state or an inactive automonitoring testing state of the leakage current detection circuit module. The appliance leakage circuit interrupter device further comprises: a trigger signal modifier circuit module which is configured to: receive the solenoid trigger signal; receive the leakage test signal; and output a corresponding solenoid trigger signal to a solenoid switching device if the leakage test signal indicates that the leakage current detection circuit module is in an active automonitoring testing state. An advantage of this arrangement is that the trigger signal modifier circuit module integrates with the functionality of the leakage current detection circuit module to enhance the functionality by issuing an extended unaltered trigger signal in circumstances where automonitoring is active so that a more reliable triggering of the solenoid can be achieved. For example, assuming the solenoid trigger signal can only be output during a negative AC wave half cycle when automonitoring in active, the leakage current detection circuit module would delay the solenoid trigger signal at least until the negative AC wave half cycle if the trigger signal happens during a positive AC wave half cycle. In another example, assuming the solenoid trigger signal can only be output during a positive AC wave half cycle when automonitoring in active, the leakage current detection circuit module would delay the solenoid trigger signal at least until the positive AC wave half cycle if the trigger signal happens during a negative AC wave half cycle. However, in examples where automonitoring is active, then the leakage current detection circuit module may output a modified solenoid trigger signal. The modified solenoid trigger signal may have a duration that is equal to the duration of the solenoid trigger signal extended by a predetermined time period. This is particularly beneficial when a leakage is detected late during an AC wave cycle such that energy to trigger the solenoid may be insufficient. The solenoid trigger signal may be output in different circumstances. For example, the solenoid trigger signal may be output during a positive AC wave half cycle, and wherein the modified solenoid trigger signal is output in a subsequent negative AC wave half cycle. In these circumstances, the predetermined time period may be selected to be sufficient to extend the modified solenoid trigger signal into a subsequent positive AC wave half cycle. Alternatively, the solenoid trigger signal may be output during a negative AC wave half cycle, and wherein the modified solenoid trigger signal is output in a subsequent positive AC wave half cycle. In this case, the predetermined time period is sufficient to extend the modified solenoid trigger signal into a subsequent negative AC wave cycle. The extension of the modified solenoid trigger signal may be between 20 and 360 degrees of an AC wave cycle, for example. A precise extension duration may be selected to suit all triggering timings. Alternatively, where the solenoid trigger signal is output during a negative AC wave half cycle, the predetermined time period may be sufficient to extend the modified solenoid trigger signal into a subsequent negative AC wave cycle. In terms of absolute time values of the duration of the trigger extension, it is envisaged that an appropriate time period for the extension may be between 5 milliseconds and 20 milliseconds. For example, the time period may be greater than 10 milliseconds, for example 15 milliseconds. In one example the trigger signal modifier circuit module is implemented as a mixed-signal integrated circuit which provides a particularly efficient implementation for the functionality. In one example, the trigger signal modifier circuit module is configured to determine that leakage test signal indicates that the leakage current detection circuit module is in an active automonitoring testing state, if the leakage test signal occurs within 360 degrees of an AC phase preceding the occurrence of the solenoid trigger signal. In another aspect of the invention, there is provided an appliance leakage circuit interrupter (ALCI) device having a self-test function. The ALCI device comprising: a leakage current detection circuit module which is configured to: receive a phase current signal from a current sensor; determine the presence of a leakage current based on the phase current signal; output a solenoid trigger signal in the event that leakage current is detected; and output a leakage test signal, that is indicative either of an active automonitoring testing state or an inactive automonitoring testing state of the leakage current detection circuit module, a trigger signal modifier circuit module which is configured to: receive the solenoid trigger signal; receive the leakage test signal; and output a modified solenoid trigger signal to a solenoid switching device if the leakage test signal indicates that the leakage current detection circuit module is in an inactive automonitoring testing state, wherein the modified solenoid trigger signal has a time duration that is equal to the time duration of the solenoid trigger signal extended in time by a predetermined time period. An advantage of this arrangement is that the trigger signal modifier circuit module integrates with the functionality of the leakage current detection circuit module to enhance the functionality by issuing a modified solenoid trigger signal in circumstances where automonitoring is inactive so that a more reliable triggering of the solenoid can be achieved. The modified solenoid trigger signal may have a duration that is equal to the duration of the solenoid trigger signal extended by a predetermined time period. This is particularly beneficial when a leakage is detected late during an AC wave cycle such that energy to trigger the solenoid may be insufficient. The solenoid trigger signal may be output in different circumstances. For example, the solenoid trigger signal may be output during a positive AC wave half cycle, and wherein the modified solenoid trigger signal is output in a subsequent negative AC wave half cycle. In these circumstances, the predetermined time period may be selected to be sufficient to extend the modified solenoid trigger signal into a subsequent positive AC wave half cycle. Alternatively, the solenoid trigger signal may be output during a negative AC wave half cycle, and wherein the modified solenoid trigger signal is output in a subsequent positive AC wave half cycle. In this case, the predetermined time period is sufficient to extend the modified solenoid trigger signal into a subsequent negative AC wave cycle. In terms of absolute time values of the duration of the trigger extension, it is envisaged that an appropriate time period for the extension may be between 5 milliseconds and 20 milliseconds. For example, the time period may be greater than 10 milliseconds, for example 15 milliseconds. In yet another aspect, there is provided a power supply system for a home appliance, the power supply system comprising: a power supply module; a current sensing and trip circuit module; and a residual current detection module. The power supply module includes an AC-DC power converter arrangement that is configured to i) receive a live AC input from a live AC circuit of the current sensing and trip circuit module, ii) receive a neutral AC input from a neutral AC circuit of the current sensing and trip circuit module, and iii) provide a DC low voltage output for connection to the home appliance and the residual current detection module. Beneficially, providing a DC low voltage output to the residual current detection module from an AC-DC converter arrangement results in a more stable, reliable and efficient power supply means. Conventionally, such a power supply would be provided from a live AC circuit e.g. by a shunt regulator which would generate higher losses and thermal waste. In one example, the current sensing and trip circuit module may comprise a current sense transformer, a trip solenoid and a circuit breaker arrangement on at least the live AC circuit thereof, and the residual current detection module may comprise a circuitry module that has a first terminal connected to the current sense transformer, a second terminal connected to the trip solenoid of the current sensing and trip circuit module, and a power supply terminal for receiving power for the circuitry module. The power supply terminal of the circuitry module is connected to the AC-DC power converter arrangement for powering the circuitry module. The AC-DC power converter arrangement may include a switched mode power supply circuitry, for example a flyback converter or a buck converter to down regulate the AC supply voltage to a level that is more appropriate for internal electronics in an energy efficient manner. Although in some examples, a direct connection may be provided between the residual current detection module and the AC-DC power converter arrangement, a further advantage may be realised by providing a backup supply circuitry which is connected to the live AC circuit of the current sensing and trip circuit module. Usefully, in the unlikely event of failure of the AC-DC power converter arrangement, the backup supply circuitry is configured to supply power to the power supply terminal of the circuitry module. The backup supply circuitry may include appropriate circuitry to convert the voltage supply from the live AC circuit to the voltage terminal of the circuitry module. In some examples, the current sensing and trip circuit module is physically separated from the residual current control module. In this respect, the two modules may be provided on different and separated circuit board substrates and may not be in contact with each other than by the electrical connections between them. The electrical connections may be provided by electrical wires, e.g. filament wires, which are flexible and which can be configured to any length desired, which provides flexibility in how the modules are arranged inside a housing. Significant packaging advantages are achieved with this approach. The connections may be electromagnet!cally shielded in some examples which can provide resilience against switching interference either from the AC mains power, the electrical contacts or the switched mode power supply. In another example, the system may be enhanced with a load switch that is configured to cut off the supply to the residual current control module when mains power is disconnected. This provides the advantage of guarding against introducing issues with the residual current detection module during user-generated test and reset actions. Optional features of aspects of the present invention may be equally applied to other aspects of the present invention, where appropriate. BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a perspective view of an embodiment of a haircare appliance incorporating a power supply system; Figure 2 is a schematic view of an example of a power supply system of the hair care appliance; Figure 3 is a series of waveform traces showing functionality of the power supply system; Figure 4 is a schematic view of another example of a power supply system of the hair care appliance; Figure 5 is a schematic view of another example of a power supply system of the hair care appliance; Figure 6 shows a series of waveforms demonstrating functionality of the power supply system in Figure 5; Figures 7 and 8 show two series of waveforms demonstrating further functionality of the power supply system in Figure 5. DETAILED DESCRIPTION Figure 1 shows a general arrangement to provide context for the invention. An electrical appliance 2 is connected to a wall box 4 of a mains power supply. The electrical appliance 2 includes an electrical supply cable 6 that extends from a main body 8 of the electrical appliance 2 and terminates in a plug 10 which is shown connected to the wall box 4 at a respective socket 12. In this example of the invention, the electrical appliance 2 is a hair dryer, for example as is available from the applicant as the Dyson Supersonic (RTM) Hair Dryer. However, the electrical appliance of the invention is not limited to hair dryers and may be any appliance with internal electronic devices that can be reconfigured to change their power draw characteristics in dependence on the territory of use. As examples, the electrical appliance may also include fans, fan heaters, blown air styling brushes, curling tongs, and so on. As has been mentioned above, the electrical appliance 2 comprises the main body 8 and the plug 10 which are connected by the electrical cable 6. The cable 6 provides appropriate wiring for supplying power from the plug 10 to the main body 8. The main body 8 comprises an outer housing or casing 14 that accommodates several functional components of the electrical appliance 2. In overview, the functional components in the main body 8 may comprise an appliance control module 16, a fan unit 18, a heater unit 20 and a heater control module 22. The plug 10 acts as the power interface between the main AC supply and the DC power requirement of the main body 8. As such, the plug 10 incorporates various electronic circuitry and electromechanical components so that it can perform a suitable power supply role safely and reliably. One such function of the plug 10 is to incorporate suitable component to provide ALCI functionality. As is known in the art, ALCI stands for ‘Appliance Leakage Circuit interrupter’. ALCI functionality and associated circuity are a requirement of various standards in territories worldwide. One such requirement is UL943B which is an industry standard governing ALCI circuits and particularly automated monitoring of those circuits. The standards set requirements for automatic monitoring of key parts of ALCI circuitry, as would be known by the skilled person. For example, one requirement is that the ALCI circuity automatic selftesting upon start-up of the electrical appliance and then periodically, within 15 minutes. Turning to Figure 2, there is shown a schematic view of the plug 10. The plug 10 comprises a housing 30 that encloses various electronics modules, as will now be described. The plug 10 comprises a live AC input 32 and a neutral AC input 34 which are provided on a first side of the housing 30, in this example. On the other side of the housing 30, there is provided a positive DC voltage output 36 and a negative DC voltage output 38. Note that for the purposes of this discussion it is immaterial which side of the housing 30 the various inputs and outputs are provided. The two voltage outputs 36,38 lead to the main body 8 of the appliance via the cable 6, shown here schematically. In overview, the modules contained by the housing 30 are a current sense and trip module (CSTM) 40, a power supply module (PSM) 42, and a residual current detection module (RCDM) 44. Together, the CSTM 40, the PSM 42 and the RCDM 44 constitute a power supply system 46 for the electrical appliance 2. With reference to each of the three modules in turn, the CSTM 40 is an assembly that incorporates several electromechanical functions relating to the AC power input to the plug 10 and serves to control the onward connection of AC power to the PSM 42. In overview, the CSTM 40 has a live AC input 50, a neutral AC input 52, a live AC output 54 and a neutral AC output 56. A live or ‘hot’ AC line or circuit 58 is connected between the live AC input 50 and the live AC output 54. Similarly, a neutral AC line or circuit 60 is connected between the neutral AC input 52 and the neutral AC output 56. The live AC input 50 is connected to the live AC input 32 of the housing 30 and the neutral AC input 52 is connected to the neutral AC input 34 of the housing 30. The CSTM 40 comprises further componentry to sense the current imbalance between the live AC line 58 and the neutral AC line 60. In this respect, the CSTM 40 comprises a current sense transformer 62, a solenoid 64, a set of contacts 66 that is actuatable by the solenoid 64 to make or break the connection along the live AC line 58 and the neutral AC line 60, a reset button 68 through which means the set of contacts 66 is resettable once broken, and a test button 70 that bridges points on the live AC line 58 and the neutral AC line 60 via an associated test bridge circuit 71 incorporating a resistor that permits, when actuated, a limited current to flow between the live AC line 58 and the neutral AC line 60 to deliver a detectable imbalance of current signal between the two lines. Further componentry, for completeness, includes a resistive fuse 63 on the live AC circuit 58 for overcurrent protection, a varistor 65 between the live AC circuit 58 and the neutral AC circuit 60 for transient voltage protection, and an LED 83 for providing a visual indication of a fault within the circuitry which will be explained in more detail below. It should be noted that the CSTM 40 is an electromechanical assembly and, as such, various components that are conventional in such devices are not shown in the schematic view of Figure 2 for the sake of clarity. Further discussion of the PSM 42 will be provided below. The PSM 42 comprises a live AC input 72 and a neutral AC input 74, and also a positive DC output 76 and a negative DC output 78. The positive DC output 76 is connected to the positive DC voltage output 36 of the housing 30 and the negative DC output 78 is connected to the negative DC voltage output 38 of the housing. An AC-DC power converter arrangement (PCA) 80 is connected between the inputs and outputs 72,74,76,78 of the PSM 42. The function of the PCA 80 is to convert the incoming AC waveform from the CSTM 40 into a DC output that is suitable for the main body 8 of the electrical appliance 2. The general functionality of the PCA 80 and, moreover, the PSM 42 would be understood by the skilled person. The PCA 80 comprises a rectifier circuit 82 (e.g. full or half-bridge rectifier circuit) that is coupled to a DC-DC converter 84. The rectifier circuit 82 has a set of AC inputs that are connected to the live AC input 72 and a neutral AC input 74 of the PSM 42, and a set of DC outputs that are connected to the DC-DC converter 84. In turn, the DC-DC converter 84 has a set of DC outputs that provide the positive DC output 76 and the negative DC output 78 of the PSM 42. The DC-DC converter 84 may be a switched-mode power supply (SMPS) as is known in the art for providing an efficient conversion of DC input voltage provided by the rectifier circuit 82. Any suitable type of SMPS would be suitable, as would be specifiable by the skilled person, such as a Buck converter or a Flyback converter. It should be noted at this point that the PSM 42 and the CSTM 40 are physically separated from one another. By this, it is meant that the electronic components such as the converter 84, the rectifier 82 and the circuit connections between them are provided on a circuit board substrate that is a separate component to the components of the CSTM. Thus, the connections between the AC outputs 54,56 of the CSTM 40 and the AC inputs 72,74 of the PSM 42 are provided by filament wires 85 extending between the modules rather than by conductive tracks provided on a circuit board substrate. In this way, there is improved flexibility in the way in which the PSM 42 may be packaged within the housing 30 which enables a more compact packaging to be achieved. The filament wires 85 may be configured to be any length to suit packaging requirements. Furthermore, they may incorporate shielding to guard against adverse electromagnetic effects. Turning now to the RCDM 44. In a general sense, the RCDM 44 provides functionality to sense current flowing through the live and neutral circuits 58,60 of the CSTM 40 and to detect an imbalance in the current flow which may occur during faulty operation of the electrical appliance 2. Such current imbalances are sometimes referred to in the art as ‘leakage currents’ as would be well understood by a skilled person. In response to detecting leakage current in the circuits 58,60, the RCDM 44 is operable to trigger operation of the solenoid 64 in the CSTM 40 which opens the contacts 66 on the live and neutral circuits 58,60 which therefore cuts power to the main body 8 of the electrical appliance 2 and makes it safe. In the art, such functionality is sometimes referred to as being provided by a ‘residual current device’ or RCD. The primary functional component of the RCDM 44 is a leakage current detection circuitry module 86. The general configuration and functionality of the leakage current detection circuitry module 86 will now be described. The leakage current detection circuitry module 86 is configured as an integrated circuit having the following pin designations: two current sensing pins, CS1 and CS2 which are connected to the current sense transformer 62; a PHASE pin, a voltage supply pin VCC, a leakage test pin L TEST, and SCR test pin, SCR TEST and an SCR trigger pin SCRTRIG. Such integrated circuit modules are generally known in the art as are the pin designations. Examples include product code NCS37020 from Onsemi Corporation, and product code FM2159 from Shanghai Fudan Microelectronics Co. Now follows a general discussion about the leakage current sensing functionality of the leakage current detection circuitry module 86 for ease of reference, although it should be noted that the general functionality is well known so a full discussion will not be provided, for brevity. In general, the function of the leakage current detection circuitry module 86 is to detect leakage currents in the electrical appliance 2 using the current sense transformer 62. The leakage current detection circuitry module 86 therefore monitors the inputs CS1 and CS2 from the current sense transformer and determines if a leakage current exists that is greater than a predetermined threshold. It has been explained above that the current sense transformer 62 is connected to the leakage current detection circuitry module 86 at inputs CS1 and CS2. In more detail, it should be noted that the solenoid 64 is connected to the live circuit 58 in the CSTM 40 and is also connected to the PHASE pin, the SCR TEST pin and the SCR TRIG pin. The purpose of this interconnection is to enable the leakage current detection circuitry module 86 to trip the solenoid and thus open the contacts 66. It does this by outputting a high signal from SCRTRIG in response to detecting a leakage current. SCRTRIG is connected to a silicon-controlled rectifier (SCR) 88 which is located in a conductive line 87 that is connected to the solenoid 64. When SCR TRIG is set high, the SCR 88 conducts which energises the solenoid 64. The PHASE pin is also connected to the conductive line 87 and, due to the presence of a diode DI and resistor RI, is exposed to a clock pulse indicating the frequency of the voltage on live AC circuit 58 as sensed through the solenoid 64. The input into the PHASE pin provides timing information about the AC cycle on the live AC circuit 58, and also provides information that the solenoid 64 is carrying current correctly. It will furthermore be noted that the CSTM 40 and the RCDM 44 are physically separated from one another. By this, it is meant that the electronic components of the RCDM 44 such as the leakage current detection circuitry module 86 and associated components like accompanying resistors and diodes are installed on a circuit board substrate that is a separate component to the components of the CSTM 40. The connections are shown generally on Figure 2 at reference label 81. Thus, the connections 81 between the CSTM 40 and the RCDM 44 may be provided by filament wires or similar components such as stamped metal connections extending between the modules rather than by conductive tracks provided on a circuit board substrate. In this way, there is improved flexibility in the way in which the RCDM 44 may be packaged within the housing 30 which enables a more compact packaging to be achieved. The connections 81 may incorporate shielding to guard against adverse electromagnetic effects. As a further enhancement to the illustrated example, a load switch may be incorporated into either the circuitry illustrated in Figure 2 or Figure 4 that is configured to cut off the supply to the leakage current detection circuitry module 86 (namely, the VCC pin) when mains power is disconnected from the electrical appliance. This may be achieved by using a clock signal generator that is synchronised to the mains power using a suitable configuration of diode, resisters and Zener diodes. The signal from the Zener diode may be fed into a comparator which generates a square wave clock signal. To detect a loss of mains voltage, a suitable integrated circuit known as a Single Retriggerable Monostable Multivibrator which can output a status signal indicating the loss of mains power. This status signal can be used to terminate the power to the VCC pin of the leakage current detection circuitry module 86 when a predetermined number of AC wave cycles have been detected as missing. Auto-monitoring of leakage current detection circuitry module 86 Although the basic function of the leakage current detection circuitry module 86 is to trigger the solenoid 64 when a leakage current is detected, it is also configured to carry out a selftesting function in order to ensure that it is operating correctly. This function is sometimes also referred to in the art as an ‘auto-monitoring’ function of the circuit. The self-test function is implemented by the LATEST pin and the SCRTEST pin. As can be seen in Figure 2, the L TEST pin is connected to semiconductor switch SI. Switch SI is located in a conductive line 89 that is connected to the live AC circuit 58 in the CSTM 40 via diode D2 and resistor R2. A further conductive line 89’ is also provided to connect the LATEST pin to the negative AC circuit 60 via a further diode D2’. The two didoes D2 and D2’ permit leakage current to flow during positive and negative half cycles, respectively. When the L TEST pin is set high, this activates the switch SI which therefore introduces a controlled leakage current from the live AC circuit 58. The leakage current is detected by the current sense transformer 62 and so the current detection circuitry module 86 is able to determine that the current sense transformer 62 is operating correctly. Once the confirmation of the ability to detect a leakage current is established, the current detection circuitry module 86 is able to self-test for correct operation of the SCR 88 and the solenoid 64. This is generally conventional functionality in such residual current detection devices, but a brief overview will be provided for context, with reference to Figure 3. Figure 3 illustrates various waveforms and pin statuses. From top to bottom, there is shown the AC cycle of the live AC circuit 58, the status of the PHASE pin which coincides with the AC cycle, the status of the LTEST pin, the level of leakage current, the status of the SCRTEST pin and the status of the SCRTRIG pin. The leakage test is only initiated in the negative half cycle which means that triggering of the SCR 88 will not cause solenoid 84 to be energised. A leakage test is initiated at time TO by the L TEST in going high. This fires switch SI which causes leakage current to flow as indicated. The leakage current is detected by the current sense transformer 62 through pins CS1 and CS2. In order to test the correct functioning of the SCR 88, the current detection circuitry module 86 triggers the SCRTEST pin to a predetermined voltage, e.g. as shown here as 3 V. The current detection circuitry module 86 senses the leakage current and, in response, sets the SCRTRIG pin to a high state at time T1. It takes a finite time for sensing to occur which may be between 2ms and 3ms for example. Typically, it may take approximately 2 ms. Triggering of the SCR TRIG pin fires the SCR 88 which pulls the predetermined voltage (e.g. 3 V) at the SCR TEST pin to ground. The current detection circuitry module 86 senses the falling edge of the SCR TEST pin and therefore can determine that the SCR 88 is operating correctly. If a fault in the system is identified, the current detection circuitry module 86 is configured to provide power to the LED 83 by way of an LED pin. In this example the LED 83 is provided on the CSTM 40 but in principle the positioning of the LED 83 is not material to its functionality and so it may be positioned anywhere on the housing 30. Power supply to residual current detection module 44 Having described in overview the main functionality of the current detection circuitry module 86, the discussion will move on to power supply aspects. An aspect that is notable about the leakage current detection circuitry module 86 is the voltage supply that is provided to it via the VCC pin. Conventionally, such an integrated circuit having leakage current detecting and auto-monitoring functionality will be provided with an input voltage from the live AC circuit 58. However, the drawback of this approach is that it requires a large resistor and associated circuitry components in order to provide an appropriate voltage input. This approach tends to be an inefficient way to provide power to such an integrated circuit and as such dissipates excessive energy as heat through the supply resistor(s). In the illustrated example, it will be noted that the PSM 42 provides a power connection to the current detection circuitry module 86. More specifically, it will be noted that the positive voltage output of the DC-DC converter 84 of the PCA 80 is connected to the VCC pin via a conductive link 90. The conductive link 90 may be composed of a conductive track portion 90a provided on a circuit substrate of the RCDM 44 and a connecting portion 90b which extends between the RCDM 44 and the PSM 42. The connecting portion 90b may be a soldered joint or may be a filament wire which would provide more flexibility in positioning the physically separated substrates of the RCDM 44 and the PSM 42. The conductive link 90 incorporates a diode D3 and a resistor R3 and capacitor C2 to ensure that the input voltage is suitable for the VCC pin. Notably, supplying power to the leakage current detection circuitry module 86 from the DC-DC converter 84 provides a more efficient power supply that dissipates less thermal energy. This is particularly the case with a high efficiency DC-DC switched-mode based converter such as a boost / buck converter, as opposed to a shunt / series-controlled regulator. Turning now to Figure 4, there is shown a further example of a power supply arrangement between the PSM 42 and the current detection circuitry module 86 of the RCDM 44. In most respects, the components shown in Figure 4, and their associated functionality, are the same as those shown in Figure 2 so this discussion will focus on the differences for the sake of brevity. Comparing Figure 4 with Figure 2, it will be noted that the current detection circuitry module 86 of the RCDM 44 is still supplied with a voltage on the VCC pin by the PC A 80, via conductive link 90. However, the example of Figure 4 provides enhanced functionality in the form of a backup power supply circuitry 92. The backup power supply circuitry 92 is shown as encompassed by the dotted lines and it will be appreciated that it is incorporated into an intermediate position in the conductive link 90 between the DC-DC converter 84 and the VCC pin. It is envisaged that the backup power supply circuitry 92 is incorporated into the circuit board substrate of the RCDM 44. The backup power supply circuitry 92 functions to maintain a voltage supply to the VCC pin in the event of a fault occurring with the DC-DC converter 84. If a fault does occur, such that the voltage output of the DC-DC converter 84 falls to 0V, then the backup power supply circuitry 92 functions to connect the VCC pin to the conductive line 89 which therefore links the VCC pin to the live AC circuit 58 of the CSTM 40. The conductor 89 and conductor 90 converge at junction Vs. Junction Vs is provided on the substrate of the RCDM 44. The connection through the conductor 89 to the live AC circuit 58 is controlled by a semiconductor switch S2. Whilst the DC-DC converter 84 is supplying a suitable voltage, the switch S2 is in an open / off position which means that the voltage at Vs is at a voltage determined by the supply voltage of the DC-DC converter 84, as adapted by the resistor R3, which is should be noted is the same as in Figure 2. The gate voltage at switch S2 is maintained in a low state by switch S3, as the drain terminal of S3 is connected to the gate terminal of S2. The gate terminal of switch S3 is connected to a voltage divider VD1 constituted by resistors R4,R5 on a branch conductor 94 from conductive link 90. The voltage divider VD1 therefore maintains the gate terminal of switch S3 at a suitable level to maintain it at a high state, which pulls the switch S2 to an off state. If the supply voltage from the DC-DC converter 84 drops to 0V, the gate terminal of switch S3 drops to 0V. The presence of a suitably biased Zener diode Zl, capacitor Cl and resistor R6 across the source and drain terminals of switch S3 biases the gate terminal of the switch S2 to a voltage which is higher than that of the source terminal of switch S2. Suitable selection of the bias value of the Zener diode Zl is considered to be within the capabilities of a skilled person. So, when the power supply from the DC-DC converter 84 fails, the switch S3 turns off due to loss of voltage at its gate terminal and so the gate terminal is biased by virtue of Zener diode Zl and capacitor Cl to a voltage higher than that at the source terminal of switch S2. This closes the switch S2 and sets the voltage VS to be the voltage at the drain terminal of switch S2 will be at a voltage determined by the live AC circuit 58 as pulled down by resistor R7 and rectified and smoothed by diode D7 and capacitor C2, which therefore supplies the VCC pin of the current detection circuitry module 86. Re-establishment of the power supply from the DC-DC converter 84 will reverse the above process and switch the power supply to the VCC pin from the live AC circuit 58 to the voltage output of the DC-DC converter 84. Beneficially, therefore, the backup power supply circuitry 92 guards against a single mode failure of the DC-DC converter 84. Extension of SCR trigger pulse Having described power supply arrangements for the leakage current detection circuitry module 86, the discussion will now turn to a further aspect of the invention with reference to Figures 5-7. Firstly, reference will be made to Figure 5 which provides a schematic view of the power supply system 46 similar to that shown in Figures 2 and 4. The following discussion will therefore focus on the differences between the system in Figure 5, which are concerned with the internal configuration of the RCDM 44. As is the case in Figure 2 and 4, the RCDM 44 comprises leakage current detection circuitry module 86, the function of which is the same as the above discussion, which is to sense a current imbalance using the current sense transformer 62 at pins CS1 and CS2 and issue a triggering signal at SCR TRIG pin in order to activate the SCR 88 which energises the solenoid 64 and opens the contacts 66 to put the system into a safe state. As before, the leakage current detection circuitry module 86 has auto-monitoring functionality, as discussed above. One issue associated with a conventional integrated circuit carrying out the role of the leakage current detection circuitry module 86 is that the auto-monitoring function can in some circumstances conflict with the normal ability of the circuity to trigger the SCR 88 correctly. This is particularly the case with certain standard requirements that specify that leakage detection circuity is required to trip with a pulsating leakage current at specific phase delays of Odeg, 90deg and 135deg, which can be challenging in the presence of conventional automonitoring processes. This is because the auto-monitoring function is reserved for use in one half-cycle of the AC cycle. As discussed above, the auto-monitoring is taking place within the negative half cycle. This can mean that leakage currents occurring late in the positive half-cycle (e.g at 135degs phase angle) do not provide sufficient actuation energy for the triggering pulse from the leakage current detection circuitry module 86 to actuate the solenoid 64. The configuration of the RCDM 44 as exemplified in Figure 5, and as discussed further below, provides a leakage current detection circuitry module 86 with enhanced functionality which overcomes this issue and ensures that the leakage current detection circuitry module 86 can correctly trigger the SCR 88 in any part of the positive AC cycle even with auto-monitoring. To this end, the RCDM 44 shown in Figure 5 also includes a further circuitry component which in this example is shown as an integrated circuit, which will be hereinafter referred to as trigger signal modifier circuit module 100. The trigger signal modifier circuit module 100 comprises the following pin designations: a TRIG IN pin, a TRIG OUT pin, a L TEST pin, a PHASE pin, a CLK pin, a power supply pin VCC, and AC status pin. The pins of the trigger signal modifier circuitry module 100 are connected to the pins of the leakage current detection circuitry module 86 in the following way: The CLK pin is connected to the PHASE pin via an associated diode and therefore provides a clock input that is timed to coincide with the timing of the AC cycle. The leakage current detection circuitry module 86 therefore receive AC phase information as in the previous examples. What is more, the PHASE pin of the trigger signal modifier circuit module 100 is connected to the conductor 87 associated with the solenoid 64 via diode D4, resistor RI and a Zener diode ZD2, and so receives the AC phase information by this means. In effect therefore, the trigger signal modifier circuit module 100 receives AC phase information through the solenoid 64 and generates a corresponding clock signal from the CLK pin to the leakage current detection circuitry module 86. This means that both the leakage current detection circuitry module 86 and the trigger signal modifier circuit module 100 are synchronised with mains power and the CLK signal input to the PHASE pin of the leakage current detection circuitry module 86 and so guards against generation of common mode noise and prevents mistriggering. The VCC pin of the trigger signal modifier circuit module 100 is connected to the DC-DC converter 84 in the same manner as described in the previous examples. However, other power supply arrangements for the VCC pin are possible. The VCC pin of the leakage current detection circuitry module 86 is connected to the DC-DC converter 84 as in the previous examples. However, other power supply arrangements for the VCC pin are possible. The AC status pin is connected to the VCC pin of the leakage current detection circuitry module 86 by way of two switches, labelled S4 and S5. The function of the switches S4, S5 will be discussed further below. The TRIG IN pin is connected to the SCRTRIG pin. Therefore, the SCRTRIG pin of the leakage current detection circuitry module 86 outputs the SCR TRIG signal to the trigger signal modifier circuit module 100. In turn, the trigger signal modifier circuit module 100 outputs a TRIG OUT signal via the TRIG OUT pin. The trigger signal modifier circuit module 100 is configured to perform a modification to the TRIG IN signal and output a modified signal as TRIG OUT in certain circumstances, as will be described in more detail later. The TRIG OUT pin is connected to the SCR 88. The TRIG OUT pin triggers the SCR 88 in the same way as the SCR TRIG pin as described in the previous examples. This will be described in more detail below. The LATEST pin of the trigger signal modifier circuit module 100 is connected to the LATEST pin of the leakage current detection circuitry module 86. By this means, the trigger signal modifier circuit module 100 receives a signal when the leakage current detection circuitry module 86 initiates a leakage test, as described above. The LATEST pin of the leakage current detection circuitry module 86 is connected to the gate of switch SI as in the previous examples. The SCRTEST pin of the leakage current detection circuitry module 86 is connected to the conductor 87 as in previous examples. In general, the functionality of the trigger signal modifier circuit module 100 is to modify the operation of the leakage current detection circuitry module 86, and specifically the trigging of the SCR TRIG signal upon detection of a leakage current, in order to extend the duration of the triggering signal that is applied to the SCR 88 thereby improving the triggering function particularly during late stages of a AC half cycle. As further background, it should be appreciated that auto-monitoring routines in commercially available integrated circuits are designed to perform during the negative half-cycle of the AC mains, while the triggering switch of the ALCI circuitry (i.e. the silicon controlled rectifier / SCR) is conductive only during the positive half-cycle of the AC mains or vice versa. However, the drawback of such approach is that the SCR will have a problem triggering if the leakage current happens at a phase angle close to the next negative half cycle. In more detail, during late stages of a phase half-cycle (e.g. after 135degs) the duration of a leakage current is very small (about 2.5ms in a 50Hz main power waveform). Due to limitations of conventional auto-monitoring functionality, triggering of the solenoid 64 can only occur in the positive half cycle of the AC mains. Due to the reaction time of the electronics which usually takes about 2.0ms, the circuitry only has around 0.5ms to trip the solenoid which is insufficient for proper operation. To guard against this, the trigger signal modifier circuit module 100 is configured to detect the triggering signal (SCR TEST) from the leakage current detection circuitry module 86 and generate an extended trigger signal which ensures that the trigger signal extends into the next positive cycle of the AC mains, allowing sufficient time for the solenoid 64 to be energized and the mechanical contacts 66 to be triggered. Moreover, the trigger signal modifier circuit module 100 is configured to avoid extending the triggering signal during an active auto-monitoring routine, which could otherwise lead to erroneous triggering. This functionality is shown pictorially in Figure 6, which shows a series of waveforms and signal traces. From top to bottom, there is shown i) a representation of the AC power cycle on the live AC circuit 58, ii) status of the PHASE pin, and therefore also the CLK pin, iii) leakage current through the live AC circuit 58, SCRTRIG signal output by the leakage current detection circuitry module 86 and therefore input to the TRIG IN pin, iv) the output of the TRIG^OUT pin, and v) the status of the LTEST pin. The waveforms represent a scenario where a leakage current arises late in the positive half cycle, for example at 135deg. Assuming the automonitoring functionality of the circuitry of the RCDM 44 takes place in the negative half cycle, this means that at latter stages of the positive half cycle there is insufficient energy available from the leakage current to serve to trigger the trip solenoid 64 effectively. As can be seen in the leakage current trace, the current level follows the degrading AC cycle from TO to Tl, where the AC cycle transitions to the negative half cycle of phase cycle AC1. The leakage current detection circuitry module 86 is configured to detect the leakage current and set the SCR TRIG pin to a high state, as has been described previously. However, the leakage detection takes a finite time to occur, which is typically around 2.0ms, as shown at ATI. It will be appreciated that at latter stages of the positive half cycle, as shown here, a very small time period exists between the leakage current occurring and the end of the positive half cycle. In a typical household AC mains power system, a 135deg phase angle to 180deg phase angle difference amounts to about 2.5ms. Therefore, on triggering of the SCRT signal, there is insufficient energy available to the solenoid to enable it to be energised. In such a scenario, the trigger signal modifier circuit module 100 is operable to detect the SCR TRIG signal and determine whether an auto-monitoring test is active. It may achieve this by checking the status of the L TEST pin which, as can be seen in Figure 6, is at a low state. The status of the L TEST pin may be determined through the previous AC phase cycle in order to determine whether an automonitoring leakage test is in an active state. Once these conditions are fulfilled, the trigger signal modifier circuit module 100 is operable to apply a modification or enhancement to the TRIG IN / SCR TRIG signal and output the modified trigger signal TRIG_OUT. It will be seen in Figure 6 that the modified trigger signal TRIG OUT is extended in duration compared to the basic, unmodified trigger signal TRIGIN / SCRTRIG. Here, the TRIG OUT signal is extended to T3 which can be seen is in the subsequent phase cycle labelled AC2. The extent to which the trigger signal modifier circuit module 100 extends the duration of the input trigger signal TRIG IN may be varied. However, as shown here, the duration of the TRIG OUT signal has been extended so that it extends into the next positive half cycle, which is shown as starting at T2 and labelled as AC2. It is envisaged that an appropriate duration of extension to the SCRTRIG signal is 15ms, which applies to a 50Hz power cycle. In a 50Hz AC power cycle, a full wave cycle is 20ms, so it will be appreciated that half a cycle is 10ms in duration. So, a 15ms extension would mean that the TRIG OUT signal would extend to at least 45deg into the next positive AC phase cycle, based on a leakage current occurring at some point after 135degs in the preceding AC phase cycle. The amount of extension into the next positive phase cycle that would be required would largely depend on the energy requirements to trigger the solenoid 64. Smaller solenoids would require less energy to trigger, so a smaller time extension into the next positive phase cycle may be sufficient. It is envisaged at this point that a time extension at least to 90 degrees into the next positive phase cycle would provide a reliable triggering of the solenoid, which equates to a 5ms extension into the next positive phase cycle. However, in some circumstances, an extension of 45 degrees may be sufficient, or 12.5 degrees. In other examples, it is envisaged that an extension of time comparable to a complete AC phase cycle, i.e. 20ms, would be an appropriate time extension. In Figure 6, the extended trigger signal, as shown by the status of the TRIG OUT pin is shown as extending 45 degrees (or 5ms, for a 50Hz cycle) into the positive cycle, and is shown extended further, in dashed lines, up to 90 degrees. The functionality in Figure 6 will now be compared with further functionality of the trigger signal modifier circuit module 100. Comparing Figure 7 with Figure 6, it will be appreciated that Figure 7 also comprises a trace indicating the SCR TEST signal as output from the SCR TEST pin of the leakage current detection circuitry module 86. As can be seen in Figure 7, the leakage current detection circuitry module 86 has initiated a leakage test at TO, as indicated by the high status of the LTEST signal. The LATEST signal issued by the leakage current detection circuitry module 86 is detected by the trigger signal modifier circuit module 100 by virtue of its respective L TEST pin. In this example, the leakage current test is being conductive at the start of a negative half cycle of AC1. The trigger signal modifier circuit module 100 is therefore able to determine that the leakage current detection circuitry module 86 is in an active testing state. That is to say, the automonitoring function is active, as opposed to the scenario in Figure 6 where the leakage current detection circuitry module 86 was in an inactive testing state, that is automonitoring is not active. As described above, during the test the leakage current detection circuitry module 86 also issues the SCRTEST signal, which sets the pin status to a predetermine voltage level e.g. 3V as discussed above. This is indicated on Figure 7 as the SCR TEST signal goes to a high state. Following the initiation of the leakage test, leakage current occurs in the same way as in Figure 6. The leakage current detection circuitry module 86 detects the leakage current via the current sense transformer 62 at pins CS1 and CS2 and issues the SCRTRIG signal. The signal is triggered at time T1 on Figure 7. The SCR TRIG signal is detected by the TRIG IN pin of the trigger signal modifier circuit module 100. In response, the trigger signal modifier circuit module 100 sets the TRIG^OUT pin to a high state, which pulls the voltage at the SCR TEST pin to a low state. The leakage current detection circuitry module 86 therefore is able to determine a proper functioning of the SCR 88. This happens at time T2. It will be noted that in this scenario, the trigger signal modifier circuit module 100 has identified that a leakage test status is active (i.e. automonitoring is in an active state) and so it determines not to extend the duration of the TRIG OUT signal as compared to the TRIG IN signal that it receives from the leakage current detection circuitry module 86. Instead, the trigger signal modifier circuit module 100 simply outputs the SCRTEST signal it receives at the TRIGIX in directly to the TRIGOIJT pin. Turning to Figure 8, it will be noted that in Figure 8 a leakage test is shown as happening in the positive half cycle of AC1. This is shown by the status of the LTEST as high between TO and Tl, and the rise in leakage current. Leakage current is terminated at Tl, by which point the leakage current detection circuitry module 86 has detected the rise in leakage current from the current transformer 62 therefore determining that it is operating correctly and also that the detection circuitry is functioning as it should. The leakage current detection circuitry module 86 waits until the negative half cycle before conducting an SCR test. This can be appreciated by the SCR TEST signal going high at time T2. As above, the SCRJTEST pin is set to e.g. 3 V by way of the testing process. In response to the SCR TEST pin, the leakage current detection circuitry module 86 fires the SCR TRIG signal. Due to the preceding occurrence of the L TEST signal, the trigger signal modifier circuit module 100 is able to determine that the leakage current detection circuitry module 86 is in an active testing state. That is to say, the automonitoring function is active, as opposed to the scenario in Figure 6 where the leakage current detection circuitry module 86 was in an inactive testing state, that is automonitoring is not active. In general, it should be considered that the leakage current detection circuit module 100 detects the presence of an active automonitoring state if the leakage test signal occurs within 360 degrees of an AC phase cycle preceding the occurrence of the solenoid trigger signal, i.e. one complete preceding AC cycle. The SCR TRIG signal is detected by the TRIG IX pin of the trigger signal modifier circuit module 100. Since the trigger signal modifier circuit module 100 has detected that an automonitoring state is active, it sets the TRIG OUT pin to a high state, which pulls the voltage at the SCRTEST pin to a low state. The leakage current detection circuitry module 86 therefore is able to determine a proper functioning of the SCR 88. This happens at time T4. It will be noted that in this scenario, in a similar manner to the scenario in Figure 7, the trigger signal modifier circuit module 100 has identified that a leakage test status is active (i.e. automonitoring is in an active state) and so is configured not to extend the duration of the TRIG OUT signal as compared to the TRIG IN signal that it receives from the leakage current detection circuitry module 86. Instead, the trigger signal modifier circuit module 100 simply outputs the SCR TEST signal it receives at the TRIG IN in directly to the TRIGOI.H pin. From the above discussion, it will be appreciated that the trigger signal modifier circuit module 100 integrates with the leakage current detection circuitry module 86 and enhances its functionality by extending the length of the SCR trigger signal in certain circumstance, notably when an auto-monitoring process is not running. The trigger signal modifier circuit module 100 may be implemented as a mixed-signal integrated circuit (IC). Figure 5 illustrates trigger signal modifier circuit module 100 and leakage current detection circuitry module 86 as separate module. However, one skilled in the art will recognise that both trigger signal modifier circuit module 100 and leakage current detection circuitry module 86 may be integrated under a single mixed-signal integrated circuit without departing from the art. It will be appreciated that integrating both modules in a single IC has the benefit of size reduction since some of the connections between the pins of respective modules would be rendered redundant, for example, SCRTRIG of leakage current detection circuitry module 86 and TRIGIN of trigger signal modifier circuit module 100. The example in Figure 5 provides a further benefit, as will now be explained. As mentioned above, the AC status pin is connected to the VCC pin of the leakage current detection circuitry module 86 by way of two switches, labelled S4 and S5. Switch S5 is located in the conductive link 102 between the VCC pin of the leakage current detection circuitry module 86 and the power connection to the DC-DC converter 84. The conductive link 102 further includes a resistor R8 to provide a suitable voltage modification as required by the VCC pin. The base terminal of switch S5 is connected to the AC-status pin of the trigger signal modifier circuit module 100. The collector terminal of the switch S4 is connected to the base terminal of switch S5. Note that both switches S4, S5 are BJTs, in this example, although other semiconductor switches would be appropriate. The trigger signal modifier circuit module 100 is operable to set the AC status pin to a low value when it detects that AC main is active. This ensures that the switch S4 is ordinarily in an open state which means that the switch S5 connects the VCC pin of the leakage current detection circuitry module 86 to the power supply. The trigger signal modifier circuit module 100 is operable to monitor for the inactivity of the AC mains in which case it will set the AC status pin to a high state. This may happen when the trigger signal modifier circuit module 100 detects that a predetermined number of AC cycles are absent, for example the absence of between 2 and 6 AC cycles, which may be 4 cycles. Upon triggering of the AC-status pin, this turns the switch S4 to a closed state which pulls the base terminal of switch S5 to low, therefore cutting the power to the VCC pin of the leakage current detection circuitry module 86. This functionality is particularly beneficial in the example of a user test function which can result in the AC mains power being disconnected for a period of time. To avoid contention between the loss of mains power, and the extended discharge time of the DC-DC converter 84 at minimum load conditions, which can span several seconds, the functionality of the trigger signal modifier circuit module 100 can avoid the leakage current detection circuitry module 86 going into an ‘end of life’ mode following a cut in mains power. The skilled person will appreciate that the examples that have been described above and illustrated in the Figures are merely indicative of the inventive concept as defined in the claims. The skilled person would understand that various features and processes of the examples in this discussion could be implemented in different ways without departing from the inventive concept as claimed herein. Some variants to the specifically illustrated examples have already been discussed above, and this does not preclude that the skilled person would be aware that other variations could be made. For example, in the above discussion where mention is made to semiconductor switches, it should be noted that the type of switch is not essential unless stated specifically and that the skilled person would understand that other semiconductor switch devices would be suitable. In an additional enhancement, it should be noted that the backup supply circuitry 92 as discussed with reference to Figure 4 may also be applied to the circuitry illustrated in Figure 5. In this case, the connection of the backup supply circuitry Vs as shown in Figure 4 may be connected as a node to the VCC pins on both the leakage current detection circuitry module 86 and also the trigger signal modifier circuit module 100. In such an arrangement, therefore, the technical advantages of the backup supply circuitry 92 would also apply to the power supply to the leakage current detection circuitry module 86 and also the trigger signal modifier circuit module 100. It should be noted in the above examples that the functionality has been described as being embodied by suitably configured integrated circuits, which would be within the ambit of a person skilled in the art. However, the skilled person would appreciate that comparable functionality may also be achieved with suitably configured microcontrollers with onboard programmable firmware.

Claims

1. An appliance leakage circuit interrupter (ALCI) device having a self-test function, the ALCI device comprising:a leakage current detection circuit module which is configured to:receive a phase current signal from a current sensor;determine the presence of a leakage current based on the phase current signal;output a solenoid trigger signal in the event that leakage current is detected; andoutput a leakage test signal, that is indicative either of an active automonitoring testing state or an inactive automonitoring testing state of the leakage current detection circuit module,a trigger signal modifier circuit module which is configured to:receive the solenoid trigger signal;receive the leakage test signal; andoutput a corresponding solenoid trigger signal to a solenoid switching device if the leakage test signal indicates that the leakage current detection circuit module is in an active automonitoring testing state.

2. The appliance leakage circuit interrupter device of Claim 1, wherein the solenoid trigger signal is output during a positive AC wave half cycle, and wherein the corresponding solenoid trigger signal is output in a subsequent negative AC wave half cycle.

3. The appliance leakage circuit interrupter device of Claim 1, wherein the trigger signal modifier circuit module is further configured to:output a modified solenoid trigger signal to a solenoid switching device if the leakage test signal indicates that the leakage current detection circuit module is in an inactive automonitoring testing state, wherein the modified solenoid trigger signal has a time duration that is equal to the time duration of the solenoid trigger signal extended in time by a predetermined time period.

4. The appliance leakage circuit interrupter device of Claim 3, wherein the predetermined time period is sufficient to extend the modified solenoid trigger signal into a subsequent positive AC wave half cycle.

5. The appliance leakage circuit interrupter device of Claim 2, wherein the solenoid trigger signal is output during a negative AC wave half cycle, and wherein the modified solenoid trigger signal is output in a subsequent positive AC wave half cycle6. The appliance leakage circuit interrupter device of Claim 5, wherein the predetermined time period is sufficient to extend the modified solenoid trigger signal into a subsequent negative AC wave cycle.

7. The appliance leakage circuit interrupter device of any one of the preceding claims, wherein the predetermined time period is greater than 5 milliseconds.

8. The appliance leakage circuit interrupter device of any one of Claims 1 to 6, wherein the predetermined time period is greater than 10 milliseconds.

9. The appliance leakage circuit interrupter device of any one of Claims 1 to 6, wherein the predetermined time period is less than 20 milliseconds.

10. The appliance leakage circuit interrupter device of any one of Claims 1 to 6, wherein the predetermined time period is 15 milliseconds.

11. The appliance leakage circuit interrupter device of any one of the preceding claims, wherein the trigger signal modifier circuit module is a mixed-signal integrated circuit.

12. The appliance leakage circuit interrupter device of any one of the preceding claims, wherein the trigger signal modifier circuit module is configured to determine that the leakage test signal indicates that the leakage current detection circuit module is in an active automonitoring testing state, if the leakage test signal occurs within 180 degrees of the AC phase preceding the occurrence of the solenoid trigger signal.

13. The appliance leakage circuit interrupter device of any one of Claims 1 to 12, wherein the trigger signal modifier circuit module is configured to determine that the leakage current detection circuit module is in an active automonitoring testing state based on a predetermined time interval from the previously active automonitoring state.

14. The appliance leakage circuit interrupter device of any one of the preceding claims, wherein the trigger signal modifier circuit module receives a clock signal synchronised with the phase current signal, and wherein the trigger signal modifier circuit module outputs a clock signal to the leakage current detection circuit module.

15. An appliance leakage circuit interrupter (ALCI) device having a self-test function, the ALCI device comprising:a leakage current detection circuit module which is configured to:receive a phase current signal from a current sensor;determine the presence of a leakage current based on the phase current signal;output a solenoid trigger signal in the event that leakage current is detected; andoutput a leakage test signal, that is indicative either of an active automonitoring testing state or an inactive automonitoring testing state of the leakage current detection circuit module,a trigger signal modifier circuit module which is configured to:receive the solenoid trigger signal;receive the leakage test signal; andoutput a modified solenoid trigger signal to a solenoid switching device if the leakage test signal indicates that the leakage current detection circuit module is in an inactive automonitoring testing state, wherein the modified solenoid trigger signal has a time duration that is equal to the time duration of the solenoid trigger signal extended in time by a predetermined time period.

16. The appliance leakage circuit interrupter device of Claim 15, wherein the solenoid trigger signal is output during a positive AC wave half cycle, and wherein the modified solenoid trigger signal is output in a subsequent negative AC wave half cycle.

17. The appliance leakage circuit interrupter device of Claim 16, wherein the predetermined time period is sufficient to extend the modified solenoid trigger signal into a subsequent positive AC wave half cycle.

18. The appliance leakage circuit interrupter device of Claim 15, wherein the solenoid trigger signal is output during a negative AC wave half cycle, and wherein the modified solenoid trigger signal is output in a subsequent positive AC wave half cycle19. The appliance leakage circuit interrupter device of Claim 18, wherein the predetermined time period is sufficient to extend the modified solenoid trigger signal into a subsequent negative AC wave cycle.

20. The appliance leakage circuit interrupter device of any one of the preceding claims, wherein the predetermined time period is greater than 5 milliseconds.

21. The appliance leakage circuit interrupter device of any one of Claims 15 to 19, wherein the predetermined time period is less than 20 milliseconds.

22. The appliance leakage circuit interrupter device of any one of Claim 15 to 21, wherein the trigger signal modifier circuit module is a mixed-signal integrated circuit.

23. The appliance leakage circuit interrupter device of Claim 15, wherein the trigger signal modifier circuit module is further configured to:output a corresponding solenoid trigger signal to a solenoid switching device if the leakage test signal indicates that the leakage current detection circuit module is in an active automonitoring testing state.

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