Electrical appliance

Abstract

An electrical appliance, comprising: a power supply module having an AC power input couplable to an AC supply, and a DC power output; an airflow generator electrically connected to the DC power output

Description

Field of the Invention The present invention relates to an electrical appliance that is configured to output a flow of heated air, and in particular but not exclusively to a haircare appliance. Background of the Invention 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. Summary of the Invention According to a first aspect, the invention provides an electrical appliance, comprising: a power supply module having an AC power input couplable to an AC supply, and a DC power output; an airflow generator electrically connected to the DC power output of the power supply module by a first electrical connection, wherein the airflow generator comprises an electric motor and a motor drive controller, and an electrical heater module electrically connected to the AC supply by a second electrical connection. The appliance further comprises a safety module configured to: monitor the electrical load delivered to the airflow generator by the power supply module; determine the presence of a fault state based on the monitored electrical load, and reduce the power supplied to the electrical heater module if a fault condition is detected. An advantage that the examples of the invention provide is to achieve a more effective product safety system through functionality that is responsive to the electrical load delivered to the airflow generator by the power supply module in order to identify a fault condition with the electrical appliance and reduce power supply to the heater assembly if a fault condition is detected. This means that the conventional approach of adding communication wires between the main body of an electrical appliance and a cable-based power supply unit in order to communicate a ‘heart beat signal’ indicating product safety can be avoided. The result is a simpler, more elegant implementation which reduces part count and improves EMC issues associated with the use of heart beat signal communication in environments where high current switching dynamics are present. Examples of the invention can also be expressed as a method of operating an electrical appliance, the electrical appliance comprising a power supply module having an AC power input couplable to an AC supply, and a DC power output; an airflow generator electrically connected to the DC power output of the power supply module by a first electrical connection, wherein the airflow generator comprises an electric motor and a motor drive controller; and an electrical heater module electrically connected to the AC supply by a second electrical connection. The method comprises: monitoring the electrical load delivered to the airflow generator by the power supply module; determining the presence of a fault state based on the monitored electrical load; and reducing the power supplied to the electrical heater module if a fault condition is detected. The invention can also be expressed as a safety processor for an electrical appliance, wherein the safety processor is configured to execute the instructions defined by a method as defined above, and also a computer program product comprising computer readable instructions which, when performed by a suitable processor, implements a method as defined above. In one example, the motor driver controller may be configured to sense a fault condition in the electrical heater module and, in response, to increase power draw by the electric motor from the power supply module, thereby triggering the determination of the fault state. In this manner a fault condition can be detected in more than one subsystem, that is to say the heater module in addition to the airflow generator, but the fault information is obtained through the same information acquisition channel since the power supply module can react to the raised current draw from the motor. This effect may be achieved through the use of a temperature-sensitive current transducer which is operable to sense unacceptably high temperatures at the heater module and to increase current / power draw through the airflow generator through a suitable interface to the airflow generator drive electronics. In one particular example, the power supply module and the safety module are located in a power supply housing, and wherein the airflow generator and electrical heater module are located in an appliance housing separate to the power supply housing which may be connected by a flexible electrical cable. In this configuration, therefore, significant components of the electrical appliance are separated from each other in different mechanical housings. This can be advantageous because power supply componentry, control componentry and other parts and subsystems can be located remote from the main body of the electrical appliance which can be exploited in order to reduce the size and mass of the main body to improve user experience. The first electrical connection between the airflow generator and the DC power output of the power supply module is provided in the flexible coupling. The power supply module may comprise suitable converter circuitry such as an AC-DC converter, which may further comprise rectifier and a DC-DC converter to provide flexibility in the power supplied to the airflow generator. In one example, the safety module may be configured to determine the presence of a fault condition based on the monitored electrical load. The fault condition may be triggered in various ways, for example upon exceedance of a predetermined threshold relating to current and / or power. Such a threshold may relate to a single instance of exceedance or may operate on a time-averaged basis. Optionally, hysteretic behaviour may be incorporated to strike a balance between reliability of sensing and avoiding false triggering. The safety module may also be configured to determine the presence of a fault condition based on the monitored electrical load by identifying that the operation of the electrical appliance is in one of a plurality of operating states, at least one of those operating states being indicative of a fault condition. The operating states may be determined by the power supply module as part of its normal operating functionality in controlling the electrical appliance. As such, the power supply module may communicate the operating states to the safety module. Likewise, the safety module may be configured to pull the operating state data from the power supply module. Alternatively, the functionality of determining operating states may be implemented in the safety module. In some examples, the safety module may be configured to operate a relay coupled between the AC supply and the electrical heater module, and wherein the safety module is configured to operate the relay to reduce the power supplied to the electrical heater module in the event that the fault condition is detected. The relay functionality may be embodied as a mechanical or electromechanical relay, or may also be embodied as a semiconductor switch device (i.e. semiconductor relay) such as a power MOSFET, SCR TRIAC and such like. In such a manner, the relay device may be isolated from the DC circuit as the safety module can trigger the relay device through an isolated input such as an opto-isolator. Optional features of aspects of the present invention may be equally applied to other aspects of the present invention, where appropriate. Brief Description of the Drawings Figure lisa perspective view of an embodiment of a haircare appliance; Figure 2 is a schematic view illustrating internal components of the haircare appliance of Figure 1; Figure 3 is a view illustrating a state transition diagram of the electrical appliance; Figure 4 is a representation of an example of the invention as a series of process steps. Detailed Description of the Invention A haircare appliance, generally designated 10, is shown schematically in Figures 1 and 2. Figure 1 depicts the haircare appliance 10 schematically from an external perspective, whereas Figure 2 provides more detail of the internal functional modules of the haircare appliance 10. The haircare appliance 10 in the embodiment of Figures 1 and 2 is a hairdryer, although it will be appreciated that some of this discussion may be applied to other types of haircare appliance, for example hair straighteners or hair curlers. The haircare appliance 10 comprises a main body 12 connected to a flexible coupling in the form of an electrical cable 14 which extends from the main body 12 and incorporates a power supply housing 16. The power supply housing 16 may incorporate various power supply and control functionality for the haircare appliance. Generally, it should be appreciated that power and control functions are distributed between the main body 12 and the power supply housing 16. The power supply housing 16 defines an enclosure that houses a number of electronic components as will be described in more detail later, and the electronic components within the power supply housing 16 are coupled to corresponding electronic components within the main body 12 by wires held within the electrical cable 14. Whilst referred to as wires, it will be appreciated that each wire may comprise more than one electrically conducting filament, for example as is the case with a braided wire, or foil shielding, with the overall structure of multiple filaments being considered a wire. A power connector 18 in the form of a plug is coupled to the opposite side of the power supply housing 16 to the electrical cable 14. The power connector 18 is configured to interact with an AC mains power supply, for example via a mains socket, to provide electrical current to the haircare appliance 10 in use. Note that although the power supply housing 16 is shown being connected to the main body 12 by the electrical cable 14, this may not be the case and the two components may be coupled or integrated together without a flexible cable. Moreover, although in Figure 1 the power connector 18 is shown at the end of an electrical cable, the power connector 18 may also be integrated into the power supply housing 16. The main body 12 defines a hollow, generally elongate, handle that is intended to be grasped by a user in use. A first portion 20 of the main body 12 is generally cylindrical in form and is suitable to be a handle to be grasped by a user. A second portion 22 of the main body 12 is curved, in this example, and therefore provides a means to direct airflow emanating from the main body 12. Note that the shape of the main body 12 is for illustrative purposes only and is not considered to be limiting to the inventive concept as defined by the claims. An air inlet 26 is located at the first portion 20 of the main body 12. The air inlet 26 takes the form of a mesh or screen, although its precise configuration is not crucial for this discussion. An air outlet 28 is located at the second portion 22. The air outlet 28 comprises an aperture through which air may flow in use. The second portion 22 therefore constitutes a nozzle part of the main body 12. The electrical cable 14 enters the main body 12 at the first portion 20 of the main body 12. A user interface 30 is formed on the first portion 20, and may take the form of one or more buttons, a touchscreen, or other combination or types of control inputs. Disposed within the main body 12 are a heater assembly 34 and an airflow generator 36. Disposed within the power supply housing 16 is a power supply module 38 and a safety module 40. Whereas Figure 1 provides an overview of the haircare appliance 10 from an external perspective, the focus of this discussion will now turn to Figure 2 which provides more detail about the internal functions and electrical configuration of the haircare appliance 10. The main body 12 of the electrical appliance and the power supply housing 16 are shown schematically in Figure 2, as being connected together by the electrical cable 14. In overview, the main body 12 comprises the airflow generator 36 and the heater assembly 34 and the user interface 30. The main body 12 further comprises motor drive circuitry 42 and a motor control module 44 operatively connected to the motor drive circuitry 42 for control purposes. The user interface 30 is operatively coupled to a user interface controller (“UI controller”) 46 which is configured to interpret control inputs from the user interface and provide appropriate control signals to the motor control module 44 for operation of the airflow generator 36. The UI controller 46 is also operatively connected to a heater controller 50 which is in turn connected to heater drive circuitry 52. The heater controller 50 receives input from the UI controller 46 based on user inputs through the user interface 30 and outputs suitable control commands to the heater drive circuitry 52 which operates the heater assembly 34 accordingly. In some examples, wireless communication functionality may be provided so that the electrical appliance 10 may be controlled remotely. It should be noted that the various controllers, electronics modules and like componentry described here may be combined into a single controller, so the illustrated example of the separate modules is for convenience of illustration. It should be noted at this point that the control of the airflow generator 46 and heater assembly 34 would be coordinated to provide a suitably heated air output based on user selected inputs. The inputs may vary based on desired airflow speed and heat output, as is typical in a heated haircare appliance. The precise form of control commands are outside the scope of this discussion. Airflow generator The airflow generator 36 is configured to be capable of generating an airflow within the main body 12, from the air inlet 26 to the air outlet 28 in use. An example of an appropriate airflow generator 36 is a motor comprising a driven impeller. One such motor is the V9 Dyson Digital Motor of Dyson Technology Limited, details of which can be found in published PCT patent application WO2017098202A1, for example. Such a motor may be a single-phase brushless permanent-magnet motor. The airflow generator 36 is electrically coupled to motor drive circuitry 42 disposed within the main body 12 by motor current wires 58. The motor drive circuitry 42 comprises suitable control electronics to provide appropriate control signals through the motor current wires 58 to the airflow generator 36. Specifics of the motor drive circuitry 42 depend on the airflow generator 36 used, but where the airflow generator 36 comprises a brushless permanent-magnet motor, such as the V9 Dyson Digital Motor of Dyson Technology Limited, the motor drive circuitry 42 may comprise a plurality of switches in the form of FETs arranged in a bridge formation. The precise configuration of motor drive circuity is considered within the capabilities of the skilled person and, as such, further discussion will not be provided so as not to obscure the main focus of the examples of the invention. The V9 Dyson Digital Motor of Dyson Technology Limited is also controlled using what is known as a “sensorless” control scheme, i.e. a control scheme that estimates a position of the rotor of the motor without using a position sensor such as a Hall sensor. A “sensorless” control scheme may calculate a rotational position of the rotor, and hence also impeller, of the motor using current and / or voltage values communicated to the motor drive circuitry 42 over the motor current wires 58. Details of appropriate “sensorless” control schemes will not be discussed herein for the sake of brevity, but a suitable “analog sensorless” control scheme is disclosed in published PCT patent application WO2013132247A1, whilst details of an appropriate “digital sensorless” control scheme can be found in GB patent application no. 1904290.2. The motor drive circuitry 42 is configured to supply DC current to the airflow generator 36 via the pair of motor current wires 58, with the motor drive circuitry 42 being controlled by the motor control module 44, which may comprise any appropriate microcontroller. The motor control module 44 is communicatively coupled to the motor drive circuitry 42 via one or more signal wires 60. The signal wire may carry appropriate control signals for control of the motor drive circuitry 42. The motor drive circuitry 42 is connected to the power supply module 38 by a pair of wires 62, providing a positive DC input 64 and a negative DC 66 input to the motor drive circuitry 42. The wires 62 pass through the power cable 14. The wires 62 are connected to a positive DC output 68 and a negative DC output 70 of the power supply module 38. The power supply module 38 also comprises a single phase AC supply, comprising, in the context of a UK supply, a live AC input 72 and a neutral AC input 74. The AC inputs are connected to the power connector 18 and therefore provide the power supply module 38 with a mains electricity supply. Note that Figure 2 is simplified for the purposes of this discussion and so power conditioning electronics that may be included in the system has not been shown for the sake of brevity. The power supply module 38 comprises an AC-DC power converter arrangement (PC A) 80, the function of which is to convert the incoming AC waveform from the power connector 18 into a DC output that is suitable for the main body 12 of the electrical appliance 2. The general functionality of the PCA 80 and, moreover, the power supply module 38 would be understood by the skilled person. The PCA 80 may comprises a suitable a rectifier circuit 81 (e.g. full or half-bridge rectifier circuit) that is coupled to a DC-DC converter 82. The rectifier circuit 80 may have a set of AC inputs that are connected to the AC inputs 72,74 of the power supply module 38, and a set of DC outputs that are connected to the DC-DC converter 82. In turn, the DC-DC converter 82 may have a set of DC outputs that provide the positive DC output 68 and the negative DC output 70 of the power supply module 38. It should be noted at this point that this disclosure provides an example AC-DC converter architecture, and the skilled person would appreciate that other architectures would be acceptable in this context to provide the same or similar functionality. The DC-DC converter 82 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 81, in the illustrated example, although in practice these are likely to be integrated structures rather than separated. Any suitable type of SMPS would be suitable, as would be specifiable by the skilled person, such as a Buck, Boost, Buck-Boost, Totempole, Forward, LLC or other converter architecture comprising a network of switches, diodes, inductors, and capacitors. The converter 82 is therefore able to provide a regulated power supply to the main body 12 and components housed therein at multiple different voltage levels as is appropriate for different operational modes of the electrical appliance 10. For example, the power supply module 38 may be operable to supply a relatively low DC voltage at a start up phase of the electrical appliance 2 in order to supply the electronics components within the main body 12 with a low DC voltage (e.g. within the order of 5-15V) for the energising of electronics circuitry and to bring the various electronics modules into a standby state ready for operation. This may be the case when the user plugs in the electrical appliance into an AC wall outlet but has not yet engaged with the user interface 30 to activate the airflow generator 36 and the heater assembly 34. On activation of these components, the power supply module 38 may be operable to increase the voltage level supplied to the main body 12 and supply higher current levels for the main operational modes of the electrical appliance 10, as will be discussed further later. Heater circuitry The form of the heater drive circuitry 52 is dependent upon a desired control scheme of the heater assembly 34, as would be understood by a skilled person, and so the specific form of the heater drive circuitry 52 may vary depending upon the heater elements (not shown) used in the heater assembly 34. The heater controller 50 may be configured to operate the heater drive circuitry 52 using a burst-fire control scheme, a phase angle control scheme, pulse-width modulation or a combination thereof, to control current flow to heater elements of the heater assembly 34 over a pair of power supply wires 85. In such embodiments, the heater drive circuitry 52 may comprises a plurality of AC switches such as TRIACs used to control current flow to the heater elements depending on an output of the heater controller 50. The heater drive circuitry 52 is electrically coupled to the power supply connector 18 by a pair of power supply wires 83 that extend within the electrical cable 14 and through the power supply housing 16. In some examples, power conditioning components such as input filters (not shown), comprising capacitive and / or inductive components or the like, may be disposed between the pair of power supply wires 83 and the power supply connector 18 within the power supply housing 16. The pair of power supply wires 83 comprise a live wire and a neutral wire 84,86. In use, the heater controller 50 is able to control current flow to the heater assembly 34, using the heater drive circuitry 52 in response to commands input by a user using the user interface 30 and communicated to the heater controller 50 via the user interface controller 46, for example to raise or lower the temperature of the heater assembly 34. In some examples, the heater controller 50 is able to communicate with the motor drive controller 44 over communication channel 94. In this way, one or the other of the motor drive controller 44 or the heater controller 50 may take the role of a master controller for the haircare appliance 10, and may be utilised to control both temperature and airflow provided by the electrical appliance 10, in use. A power relay module 90 is coupled to the AC supply between the power connector 18 and the heater drive circuitry 52. In this example, the power relay module 90 is housed within the power supply housing 16. The power relay module 90 may comprise a suitable mechanical, electronic, or electromechanical relay contacts which enables the power relay module 90 to make or break the electrical AC circuit between the AC supply and the heater assembly 34 and the heater drive circuitry 52. More specifically, the power relay module 90 may comprise a relay coil or solenoid 92 which is operatively coupled to a relay switch 94. As would be understood by a skilled person, the relay coil 92 is energisable in order to control the connection state of a relay switch 94 in order to allow power to be transmitted along power wires 83 to the heater drive circuity 52 or to reduce or cut the transmitted power in order to place the heater drive circuitry 52 and the heater assembly 34 into a safe state. In this sense, the heater assembly 34 may be a high-load component with a potential power dissipation of between 500W and over 3000W. A safety module 100 is provided. In this example, the safety module 100 is operatively coupled to the power relay module 92. More specifically, in this example the safety module 100 is coupled to respective terminals of the relay coil 92 by control lines 101,102. In this way, the safety module 100 is operable to energise and deenergise the relay coil 92 in order to trigger a change in state of the relay switch 94 in order to control the connection status of the AC circuit to the heater drive circuitry 52. The safety module 100 is configured to execute a safety monitoring strategy to ensure the safe operation of the electrical appliance 10. In particular, the safety module 100 is configured to operate the power relay module 90, and thereby control the flow of power to the heater assembly 34 based on the electrical load supplied by the power supply module 38. Since the power supply module 38 supplies power to the airflow generator 36, it is important that the airflow generator 36 is operating without faults in order for power to be applied to the heater assembly 34 safely. The safety module 100 is therefore configured to ensure that a fault state is not in existence and to control the state of the power relay module 90 accordingly. Safety systems in electrical appliances are known in the art. However, conventional approaches relay on the use of monitoring hardware established proximal to the electrical loads in the main body of the electrical appliance which communicate to a power supply module by way of a so-called ‘heart beat’ communication signal that is transmitted down a set of communication wires from the main body of the appliance to a safety monitoring system located at or proximal to the power supply. In conventional safety monitoring systems, such heat beat signals require additional communication wires which are housed within the electrical cables between the electrical appliance and a remote power supply box which typically houses power supply circuity. The additional wires in the electrical cable increases the thickness of the cable, which is preferable to avoid. Moreover, the heartbeat signal requires transmit and receive electronics distributed about the main body of the electrical appliance and the power supply box, which adds complexity, in part due to the additional electronics and also because further electromagnetic compatibility requirements need to be met in order to ensure that the heart beat signals are not effected by switching noise from the motor drive electronics. Advantageously, the approach provided by the examples of the invention achieves a more effective implementation through functionality that is responsive to the electrical load delivered to the airflow generator 36 by the power supply module 38 in order to identify a fault condition with the electrical appliance and reduce power supply to the heater assembly 34 if a fault condition is detected. A fault condition may be identified based on one or more thresholds of relevant electrical characteristics such as supplied current or power which are classifiable as being representative of an unallowable situation on which action needs to be taken. Suitable hysteresis behaviour may be applied to said one or more thresholds to allow some temporary exceedance of the one or more thresholds before power cut out action is implemented. Multiple different thresholds regarding suitable power-related electrical characteristics such as current and power may be implemented to represent fault conditions. Time-related thresholds may also be implemented to guard against false tripping of thresholds. The safety module 100 is shown here as being implemented as a separate component to the power supply module 38 and the relay module 90. This is for convenience of illustration and description only. It should be noted that the functionality described here may be implemented into software, firmware or hardware components integrated with the power supply module 38, the relay module 90 or, indeed, into separate microcontroller circuitry. As has been mentioned above, the functionality provided by the safety module 100 is configured to monitor the electrical load supplied to the motor drive circuitry 42 by the power supply module 38. This may be achieved by different means. In one example, the safety module 100 may be coupled to one or both of the DC supply wires 62 supplying DC power (in this example) between the power supply module 38 and the motor drive circuitry 42. The coupling between the safety module 100 and the DC supply wires 62 is shown in dashed lines in Figure 2 as an optional / alternative coupling and denoted as reference ‘106’. The safety module 100 may also be configured to monitor operation of the power supply module 38 internally to access information and electrical characteristics that are indicative of the electrical load supplied by the power supply module 38 to the airflow generator 36. For example, the power supply module 100 may be configured to communicate with internal state circuitry 110 integrated within the power supply module 38. The internal state circuitry 110 may be conventional hardware or firmware that is operable to identify operating states of the electrical appliance based on the load supplied. Therefore, it can be considered that the safety module 100 is operable in some examples to identify a plurality of operating states associated with the electrical appliance, and, more particularly, operating states of the motor drive circuitry 42 associated with the airflow generator 36. The safety module 100 may be configured to identify the plurality of operating states by monitoring the electrical load supplied to the airflow generator 36 directly, for example by measuring, sensing or otherwise determining the power draw over the power supply wires 62 to the motor drive circuitry 42. Alternatively, the safety module 100 may be configured to infer the operating state of the electrical appliance 10 by communicating with another function of the appliance 10 e.g. the internal state circuitry 110 integrated within the power supply module 38. By way of further explanation, Figure 3 provides an illustration of a plurality of operating states for the electrical appliance 10. The graph in Figure 3 provides voltage on the y-axis and current on the x-axis. The graph therefore provides an indication of the power draw of the electrical appliance 10 from the power supply module 38 during operation. The operating states shown in Figure 3 and discussed below may be conventional power supply behaviour that is implementable by a conventional power supply module of an electrical appliance in order to manage the power supplied to the load in a way that is safe for a user. In overview, the plurality of operating states include: (1) power off state; (2) standby state; (3) transition state; (4) normal operating state; (5) recoverable overload state; (6) fault condition state - reduce power; (7) fault condition - safe state (8) reset / disable state. The discussion will now provide further explanation of each of the operating states (1) through to (8). Operating state (1) - power off state. This operating state corresponds to the electrical appliance 10 being unplugged from the main supply. Here, it will be noticed that power draw is zero as the operating state corresponds to the origin of the graph at which voltage and current are at zero. Operating state (2) - standby. This operating state corresponds to a scenario where the electrical appliance 10 has been plugged into the AC mains supply and so has a source of electrical power available to it. The power supply module 38 will therefore supply a relatively low voltage to the electronic circuitry within the main body 12 to ready the electrical appliance 10 for operation. Typically, therefore, this operating state corresponds to the electrical appliance 10 being plugged into the mains supply but waiting to be used. The user interface 30, the UI controller 46, the motor controller 44, the motor drive circuitry 42, the heater controller 50 and the heater drive circuitry 52 may therefore be supplied with standby power in readiness for operation. As can be seen in Figure 3, the voltage level is relatively low in this operating state, and can be considered to be between 5V and 15V for example, although this is not essential. As can also be seen, the current draw can vary at this voltage level, depending on the requirement of the electronics during standby. Operating state (3) - transition state. This state corresponds to a transition state where the electrical appliance 10 has been commanded to operate and in response the power supply module 38 is configured to transition from the standby state (operating state (2)) to a normal operation state (operating state (4)). This may correspond to the motor drive circuitry 42 preparing to drive the airflow generator (36) e.g. by drawing more power as it charges the high side ‘boot strap capacitors’ to ready the switching circuits associated with the airflow generator 36. Operating state (3) is envisaged to last for a relatively short period of time, in the region of less than one second, although this is just exemplary. Notably, operating state (3) has hysteretic behaviour such that the power supply module 38 can increase and decrease power supply (increase and decrease voltage and / or increase and decrease current) within this region and return to operating state (2). It should be also noted that the hysteretic behaviour adds stability to the system but is not essential for the system to operate with acceptable performance. Operating state (4) - normal operating state. As will be noted in Figure 3, at this operating state the power supply module 38 is outputting a substantially constant voltage, which is significantly higher power than is supplied at operating state (2). For context, an operating voltage of between 20V and 40V may be acceptable, by way of example only. In this operating state it can be considered that a user of the electrical appliance 10 has operated the user interface 30 in order to turn on the electrical appliance 10, thereby commanding activation of the airflow generator 36, and also activation of the heater assembly 34 is a heated airflow is required, which is generally optional in hairdryers which can blow heated and unheated air. In this operating state, it can be appreciated that the current flow is permitted to cover a range of values, commensurate with normal operation of the appliance based on a varying load of the airflow generator 36 as it may be required to operate over multiple airflow settings in accordance with user preferences. Operation of the electrical appliance 10 may proceed through operating states (1) to (4) consecutively, and operation may be reversed from operating state (4) back through to (2) and / or (1). This corresponds to normal usage of the electrical appliance 10 where the user may plug the appliance in and turn it on, in which case operating states (1) through (4) would be run through promptly. Conversely, in the event that the user deactivates the electrical appliance 10 using the user interface 30, operating state (4) would switch to operating state (2) through the transition state (3) consecutively. This is illustrated in Figure 3 by virtue of the hysteretic behaviour of the power supply module 38. Operating state (5) - recoverable overload state. This operating state represents a ‘fold-out’ region of the power supply module 38 which, as a skilled person would understand, provides some flexibility for the power supply in tolerating reduced impedance of the electrical load, that is, the airflow generator 36. In this region, the power supply module 38 limits the power output by reducing the voltage supplied. The supply of electrical current may be constant in this region although it may be allowed to increase slightly. Operating state (5) is a recoverable state and, as such, if the impedance of the electrical load increases again, the electrical appliance 10 will transition back to operating state (4). If impedance of the electrical load continues to decrease, thereby increasing the current draw, then the power supply module 38 identifies that a fault condition exists within the airflow generator 36. A reduction in impedance of the load may be the result of a motor stall which may occur due to a locked rotor such that there is saturation of the electric field within the windings of the motor. In the event of identifying a fault condition, the system will move to through operating state (6) thereby indicating a fault by which means the power supply module 38 will reduce the voltage on the power supply, which will result in operating state (7). Transition from operating state (6) to operating state (5) is not permitted in this example. Operating state (7) fault condition safe state. In this operating state, the power supply module 38 is supplying the electronics in the main body 12 with a low voltage which may be sufficient to keep those electronics electrically active, but which is insufficient to activate the motor drive circuitry 42. Through this operating state, the power supply module may return the appliance to operating state (8) at which point there is the option to disable the electrical appliance entirely (operating state (1)) or return to operating state (2), the choice of which may depend on the fault that has occurred within the airflow generator 36. Note at this point that there may be more or fewer operating states of the electrical appliance from the ones shown in Figure 3. Based on the above discussion, it will be appreciated that the safety module 100 may be configured to determine that a fault condition is present by monitoring the state information of the power supply module 38 and detecting that a fault state has been entered into, for example operating states (6) and / or (7) in the discussion above. On detecting the presence of a fault state, the safety module 100 is then operable to terminate power to the heater assembly 34 by triggering the relay coil 92 to sever the supply of AC power to the heater drive electronics 52 by opening the relay switch 94. As an enhancement to the functionality of the safety module 100 as described above, further functionality may be incorporated to communicate operational information about the heater assembly 34 to the power supply module 38 and / or the safety module 100 in order to contribute to the determination about whether there is a fault condition present within the electrical appliance. A specific instance of this functionality will now be explained. In the example illustrated in Figure 2, a temperature responsive function 112 is provided. The temperature responsive function is operable to cause electrical current to be drawn from the power supply module 38 by the motor drive circuitry 42 based on the operation of the heater assembly 34 and, in particular, the temperature of the heater assembly 34. More specifically, the temperature responsive function or module 112 may be configured to determine the temperature of the heater assembly 34 and cause an increase in load current to be drawn from the power supply module 38 if the temperature of the heater assembly 34 starts to approach levels that may be considered to be unsafe. This functionality may be achieved by a suitably configured thermistor (for example a negative-temperature coefficient resistor) that is operable to cause a small additional electrical current from the power supply module 38 when the heater assembly is within a target operating temperature range. With cross reference to the operating states of Figure 3, the effect of this small additional current caused by the temperature responsive function 112 would be to move the operating point of the electrical appliance 10 sideways along the graph within operating state (4). However, in the event that the temperature of the heater assembly 34 increases into an allowable over / upper temperature range, or zone, then the temperature response function 112 is operable to increase the current drawn by the motor drive circuitry 42 from the power supply module 38 to a current level that would be sufficient to transition the power supply module 38 into operating stage (6). As has been discussed above, the transition into operating state (6) would cause the safety module 100 to identify a fault condition and therefore the power relay module 90 would be triggered thereby cutting AC power supply to the heater assembly 34. In the above discussion, it will be noted that the temperature responsive function 112 may be achieved by integrating a suitable NTC resistive element into the heater assembly 34. The NTC resistive element would therefore communicate safety information about the heater assembly 34 to the power supply module 38, albeit indirectly via the motor drive circuitry 42. This functionality may be performed in different ways. For example, indirect sensing approaches may be used to avoid embedding an NTC element within the heater assembly 34 and maintain an isolation barrier between the AC electronics of the heater assembly 34 and the DC electronics of the airflow generator 36. Still further, optical circuitry could be used to maintain a sufficient isolation barrier. The functionality of the safety module 100 is further illustrated in an exemplary manner in Figure 4 by a series of functional steps 202-206, which together form operational method 200. The functional steps 202-206 as summarised below, and as described above, may be implemented by the safety module 100 provided with a suitable processing environment such as appropriate microcontroller circuitry or application-specific integrated circuity to perform the method 200, as would be understood by a skilled person. At step 202 the safety module 100 is operable to monitor the operating state of the electrical appliance 10 and particularly the power / electrical load that is drawn by the airflow generator 36 from the power supply module 38. This can be achieved through various approaches, as has been discussed above, for example by monitoring the current drawn by the airflow generator and comparing the current load with one or more thresholds indicative of a fault condition of the airflow generator, or the safety module may monitor for the occurrence of a plurality of operating states associated with the electrical appliance with the target of identifying a fault state associated with the airflow generator 36. Step 204 corresponds to the identification of a fault condition by the safety module 100, in response to which the safety module is operable to reduce the power supplied to a different subsystem of the electrical appliance by triggering a power relay, as indicated at step 206. The skilled person would appreciate that variations may be made to the specific embodiments discussed above, and illustrated in the accompanying Figures, without departing from the inventive concept as defined in the claims. For example, in the above disclosure, the safety module 100 is monitoring the electrical load delivered to the airflow generator 36 by the power supply module 38 and from that monitoring is able to determine the state of the electrical appliance 10 and therefore identify a fault condition. Expressed in another way, the system uses electrical load to communicate information about the fault state of the electrical appliance. Possible implementations to achieve this result have been described above. However, the skilled person would appreciate that other implementations that have not been disclosed here may achieve the same or similar effect. For example, it is conventional in power supply circuits to have power factor correction functionality, which is typically abbreviated to ‘PFC’. The skilled person will appreciate that this is conventional functionality that is provided in AC-DC converter circuitry in order to reduce voltage ripple on the DC output voltage of an AC-DC converter which, in more extreme examples, can influence adversely the mains supply by generating unpredictable increases in reactor power. Therefore, conventional converter circuitry incorporates voltage boosting functionality which drives up the DC voltage, and reduces the current, which improves the harmonic content of the output signal making them more effective at being filtered to acceptable ripple levels using the inbuilt output filtering systems. In such converter systems, PFC functionality will typically operate at medium to high loads as the current draw increases. However, as a protection measure the PFC functionality will be deactivated during extreme loads to avoid overloading the PFC function. In such cases, the power supply circuit would deactivate the PFC function and pass a large ripple voltage until the excessive electrical load is removed. This functionality can be used to communicate state information about the electrical appliance, and particularly the DC electrical load, to the safety module in the above examples. In an alternative example, therefore, the safety module may be provided with functionality, through monitoring the electrical output of the power supply module, to identify when 5 PFC functionality is indicative of a fault condition in the electrical load and can therefore operate to reduce the electrical output to the AC system, for example my operating the relay device. Although the examples of the invention have been described in the context of a haircare 10 appliance, it will be appreciated that the disclosure is applicable to other electrical appliances that provide a source of heated air, such as space heaters. 15

Claims

1. An electrical appliance, comprising:a power supply module having an AC power input couplable to an AC supply, and a DC power output;an airflow generator electrically connected to the DC power output of the power supply module by a first electrical connection, wherein the airflow generator comprises an electric motor and a motor drive controller;an electrical heater module electrically connected to the AC supply by a second electrical connection;a safety module configured to:monitor the electrical load delivered to the airflow generator by the power supply module;determine the presence of a fault state based on the monitored electrical load, andreduce the power supplied to the electrical heater module if a fault condition is detected.

2. The electrical appliance of Claim 1, wherein the motor drive controller is further configured to sense a fault condition in the electrical heater module and, in response, to increase power draw by the electric motor from the power supply module, thereby triggering the determination of the fault state.

3. The electrical appliance of Claim 1 or 2, wherein the power supply module and the safety module are located in a power supply housing, and where in the airflow generator and electrical heater module are located in an appliance housing separate to the power supply housing.

4. The electrical appliance of Claim 3, wherein the power supply housing and the appliance housing are connected by a flexible coupling.

5. The electrical appliance of Claim 4, wherein the first electrical connection between the airflow generator and the DC power output of the power supply module is provided in the flexible coupling.

6. The electrical appliance of Claim 5, wherein the second electrical connection between the electrical heater module and the AC supply is provided in the flexible coupling.

7. The electrical appliance of any one of Claims 1 to 6, wherein the safety module is configured to determine the presence of a fault condition based on the monitored electrical load, if the electrical power drawn from the power supply module by the airflow generator exceeds at least one predetermined threshold.

8. The electrical appliance of any one of Claims 1 to 6, wherein the safety module is configured to determine the presence of a fault condition based on the monitored electrical load by identifying that the operation of the electrical appliance is in one of a plurality of operating states, at least one of those operating states being indicative of a fault condition.

9. The electrical appliance of any one of the preceding claims, wherein the safety module is configured to operate a relay device coupled between the AC supply and the electrical heater module, and wherein the safety module is configured to operate the relay device to reduce the power supplied to the electrical heater module in the event that the fault condition is detected.

10. A method of operating an electrical appliance, the electrical appliance comprising: a power supply module having an AC power input couplable to an AC supply, and a DC power output; an airflow generator electrically connected to the DC power output of the AC-DC converter by a first electrical connection, wherein the airflow generator comprises an electric motor and a motor drive controller; and an electrical heater moduleelectrically connected to the AC supply by a second electrical connection; wherein the method comprises:monitoring the electrical load delivered to the airflow generator by the power supply module;5 determining the presence of a fault state based on the monitored electrical load;andreducing the power supplied to the electrical heater module if a fault condition is detected.10 11. A safety processor for an electrical appliance, wherein the safety processor isconfigured to execute the instructions defined by a method in accordance with Claim 10.

12. A computer program product comprising computer readable instructions which, when performed by a suitable processor, implements a method in accordance with Claim 15 10.

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