Hair styling apparatus

Abstract

This invention relates to apparatus and methods for regulating a parameter on a handheld appliance, such as a hair styling appliance. A hair styling apparatus comprises a body having at least one arm bearing a hair styling heater; a temperature sensor arranged to sense a temperature of the hair styling heater and generate a temperature sense signal; and a power supply unit comprising a magnetic energy transfer element, an AC input coupled to a first side of the magnetic energy transfer element, a heater drive output coupled to a second side of the magnetic energy transfer element and to the hair styling heater to power said hair styling heater, and a power controller configured to regulate the heater drive output. A power controller is coupled to the temperature sense signal and configured to regulate the heater drive output of the power supply so as to control the temperature of the hair styling heater responsive to the temperature sense signal.

Claims

1. A hair styling apparatus comprising a body having at least one arm bearing a hair styling heater for heating hair to be styled; a temperature sensor arranged to sense a temperature of the hair styling heater and to generate an electrical temperature sense signal that depends on the sensed temperature of the hair styling heater; and a power supply unit comprising a transformer having a primary winding on a first side and a secondary winding on a second side, an AC input and a primary side switch coupled to the first side of the transformer, a heater drive output coupled to the second side of the transformer element and to the hair styling heater to power said hair styling heater, and a power controller configured to regulate the heater drive output by controlling an input to the first side of the transformer element, wherein the power controller is coupled to the temperature sense signal; and wherein the power controller is configured to regulate the heater drive output of the power supply in multiple steps by adjusting a duty cycle of the primary side switch so as to control the temperature of the hair styling heater responsive to the temperature sense signal.

2. The hair styling apparatus as claimed in claim 1, wherein the heater drive output is a low voltage output to supply a voltage of less than 100V.

3. The hair styling apparatus as claimed claim 2, wherein the power supply unit is configured to provide a maximum heater drive output voltage of 24V or 12V.

4. The hair styling apparatus as claimed in claim 1, further comprising: a second said arm bearing a second said hair styling heater; and a second said temperature sensor arranged to sense a temperature of the second said hair styling heater and generate a second said temperature sense signal, wherein the power supply unit further comprises a second heater drive output coupled to the secondary side of the transformer to power the second hair styling heater; wherein the power controller is further coupled to the second temperature sense signal; and wherein the power controller is configured to regulate the output voltage of the second heater drive output of the power supply so as to control the temperature of the second hair styling heater responsive to the second temperature sense signal fed back from the second temperature sensor.

5. The hair styling apparatus as claimed in claim 1, wherein the power controller is configured to disable the heater drive outputs responsive to the temperature sense signal exceeding a threshold value.

6. The hair styling apparatus as claimed in claim 1, wherein the hair styling apparatus is a hair straightener or hair crimper.

7. The method of controlling the temperature of the hair styling heater of the hair styling apparatus of claim 1, the method comprising: sensing a temperature of the hair styling heater and generating an electrical temperature sense signal that depends on the sensed temperature of the hair styling heater; and controlling the switching of a primary side switch coupled to the first side of the transformer responsive to the temperature sense signal to regulate the heater drive output of the power supply unit so as to control the temperature of the hair styling heater.

8. The method as claimed in claim 7, comprising insulating the temperature sensor from a heater plate of the hair styling heater so as to isolate the temperature sense signal from the secondary side of the transformer.

9. The method as claimed claim 7, wherein the controlling disables the heater drive output responsive to the temperature sense signal meeting or exceeding a reference voltage.

10. The method as claimed in claim 7, wherein the power supply is external to the body of the hair styling apparatus.

11. The method as claimed in claim 10, comprising coupling the power supply to the body via an electrical cable, and routing the temperature sense signal to a power controller of the power supply via a return path in the electrical cable.

12. The hair styling apparatus as claimed in claim 1, wherein the temperature sensor is electrically insulated from a heater plate of the hair styling heater so as to isolate the temperature sense signal from the secondary side of the transformer.

13. The hair styling apparatus as claimed in claim 1, wherein the power controller is configured to disable the heater drive output responsive to the temperature sense signal meeting or exceeding a reference voltage.

14. The hair styling apparatus as claimed in claim 1, wherein the power supply unit is external to the body of the hair styling apparatus.

15. The hair styling apparatus as claimed in claim 14, wherein the external power supply unit comprises a power switch for turning the hair styling apparatus on and off; wherein the power supply unit is coupled to the body via an electrical cable, and wherein the temperature sense signal is routed to the power controller via a return path in the electrical cable.

16. The hair styling apparatus as claimed in claim 1, wherein the hair styling heater comprises: a metal sheet or plate; an oxide layer comprising an oxide of said metal on a surface of said metal sheet or plate; and a heater electrode over said oxide layer, wherein the heater electrode is coupled to the heater drive output.

17. The hair styling apparatus as claimed in claim 1, wherein the temperature sense signal is modulated onto one or more wires carrying power to the hair styling heaters.

18. A power supply unit for a hair styling apparatus, the hair styling apparatus comprising: a body having at least one arm bearing a hair styling heater for heating hair to be styled; and a temperature sensor arranged to sense a temperature of the hair styling heater and to generate an electrical temperature sense signal that depends on the sensed temperature of the hair styling heater, the power supply unit comprising: a transformer; an AC input and a primary side switch coupled to a first side of the transformer; a heater drive output coupled to a second side of the transformer for powering a said hair styling heater; a sense input to receive the temperature sense signal; and a power controller coupled to the sense input, wherein the power controller is configured to regulate the output voltage of the heater drive so as to control the temperature of the hair styling heater in multiple steps by adjusting a duty cycle of the primary side switch responsive to a change in the temperature sense signal.

19. The power supply unit as claimed in claim 18, wherein the heater drive output is a low voltage output configured to supply a voltage of less than 100V.

20. The power supply unit as claimed in claim 18, further comprising a primary side switch coupled to the primary winding, wherein the power controller is configured to regulate the heater drive output responsive to the temperature sense signal by controlling switching of the primary side switch coupled to the primary winding.

21. A hair styling apparatus comprising: a body having at least one arm bearing a hair styling heater, a temperature sensor arranged to sense a temperature of the hair styling heater and to generate an electrical temperature sense signal that depends on the sensed temperature of the hair styling heater; a power supply unit external to the body, the power supply unit comprising a transformer, AC input coupled to a first side of the transformer to receive mains AC power, and an output coupled to a secondary side of the transformer; and a heater controller circuit coupled to the output of the power supply, the hair styling heater, and to the temperature sense signal, wherein the heater controller circuit is configured to drive the hair styling heater responsive to the temperature sense signal in multiple steps by controlling an input to the first side of the transformer, and wherein the heater controller circuit is located within the power supply unit external to the body of the hair styling apparatus.

22. The hair styling apparatus as claimed in claim 21, wherein the power supply unit is coupled to the body via an electrical cable, and wherein the temperature sense signal is routed to the heater control circuit via a return path in the electrical cable.

23. The hair styling apparatus as claimed in claim 21, wherein the body further comprises a second arm bearing a second hair styling heater, and wherein the hair styling heater and the second hair styling heater are connected in series or parallel.

24. The hair styling apparatus as claimed in claim 23, further comprising a second said temperature sensor arranged to sense a temperature of the second hair styling heater and to generate a second temperature sense signal, wherein the heater controller circuit is further coupled to the second temperature sense signal; and wherein the heater controller circuit is configured to drive the second hair styling heater in response to the second temperature sense signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the invention and to show how it may be carried into effect reference shall now be made, by way of example only, to the accompanying drawings in which:

(2) FIG. 1 shows an example hair styling apparatus for straightening hair according to the prior art;

(3) FIG. 2 shows an example of a power supply and heater control system for driving heater plates;

(4) FIG. 3 shows further details of the power supply and heater control system of FIG. 2;

(5) FIG. 4 shows an example embodiment of a hair straightener having a slimline housing;

(6) FIG. 5 shows the hair styling appliance of FIG. 4 with a separate power supply and control unit;

(7) FIG. 6 shows a block diagram of a first embodiment of a hair styling appliance with a modified power supply and control system;

(8) FIG. 7 shows a block diagram of a second embodiment of a hair styling appliance with a modified power supply and control system;

(9) FIG. 8 shows a block diagram of a third embodiment of a hair styling appliance with a modified power supply and control system;

(10) FIG. 9a provides a comparison of the modified power supply and control system with that of FIG. 3;

(11) FIG. 9b shows further details of the power supply and control system for use in a hair styling appliance; and

(12) FIGS. 10a-c shows three variants of the hair styling apparatus incorporating the combined power and control module.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(13) FIG. 2 shows an example of an electrical system 20 for a hair styling apparatus/appliance. A power supply circuit is formed from a power supply unit 22 with voltage feedback 25 to generate a regulated dc voltage. The controller, or heater control unit 25, controls delivery of a voltage, often DC, to the heater plates 26. The heater plate temperature is sensed by a temperature sensor, often a thermistor, or other form of temperature sensing device. A feedback loop from the temperature sensor to the heater control unit 24 is used to monitor and adjust power delivery to retain the temperature at a generally even temperature.

(14) FIG. 3 shows further details of the components forming the power supply 22 and heater control unit system 24 of FIG. 2. The power supply unit 22 connects to a mains AC input 21. In the power supply unit 22, rectification module 221 converts the AC input waveform into one having a constant polarity. Typically a full wave rectifier may be used, using a four diode rectifier bridge for example. Power supply controller 222 controls switching of a power transistor on the primary side of transformer 223. A rectifier on the secondary side of transformer 223 converts the AC signal to an output DC voltage for powering components of the hair styling apparatus. The output voltage is fed back, typically via an opto-isolator, to the power supply controller 222 to regulate the voltage delivered to the heater control unit and heater plates.

(15) A heater control unit 24 provides thermal control, controlling delivery of power to heaters for heating the heatable plates 26. The heater control unit is typically powered from the output DC voltage of the power supply, switching the heaters on and off according to heating requirements.

(16) The heater control unit 24 incorporates a local power supply unit 242. This may, for example, provide a voltage converter/regulator to power the processor (converting from 12V to 5V for example).

(17) A processing element 243, such as a microcontroller controls operation and in particular, power delivery to the heatable plates 26. The processing element may also be coupled to a user interface allowing different modes of operation to be set. The user interface may be one or more switches for example including a power switch and temperature/mode switch. The processing element may also be used to control user feedback, generating alerts or signals, visually via an indicator light or audibly via a speaker. This feedback may be used to indicate the status of the hair styling appliance to a user, such as indicating that the heatable plates are within a recommended temperature operating range, or reminding a user that the apparatus is on, and may need to be turned off.

(18) Connected to and under control of the processing element 243, power control unit 241 controls delivery of power to the heatable plates 26. The power control unit switches the heatable plates on and off according to signals from the processing element 243.

(19) A temperature sensor (e.g. a thermistor) 244 is thermally coupled to each heatable plate 26, sensing temperature and providing a temperature sense signal to the processing element. The processing element can then control operation of the heatable plates in response to the temperature feedback.

(20) FIG. 4 shows a side view of an illustrative embodiment of a hair styling apparatus 40 having a slimline housing. The styling apparatus is formed into a pair of hand-held styling tongs having two arms 44a, 44b, arranged so that when squeezed together the heatable plates 46a, 46b positioned on each arm 44a, 44b approach one another to allow hair to be clamped between. As can be seen in FIG. 4, the arms of the example embodiment are slimmer than many conventional hair straighteners, meaning that there is limited space to housing the power supply and heater control electronics.

(21) In FIG. 5, the hair styling apparatus is separated into two separate units: the hand-held styling tongs and an external unit 52. Components of the power supply and/or heater control electronics of the hair styling apparatus are now located in the external unit 52, remote to the hand-held styling tongs 40. This reduces the components in the hand-held styling tongs, reducing the space required and reducing the weight of the tongs. The external unit 52 connects to the mains AC input via a multi-core cable, then via another multi-core cable to the hand-held styling tongs. In use, the external unit would typically rest on the floor, connected via a cable of approximately two metres or more to the tongs. The external unit may incorporate a power switch 54 allowing a user to turn the hair styling appliance on or off. An LED indicator 53 may also be present to provide visual feedback that the apparatus is on. A temperature control switch or dial may also be present.

(22) FIGS. 6-9 show further details of how the hair styling apparatus of FIG. 5 may be implemented.

(23) The circuit arrangements shown in FIGS. 6-9 include example embodiments using low voltage heaters, capable of being driven by a voltage of below 100V, for example voltages 12-24V (although higher voltages, such as 36V, 50V or more may be used). The low voltage heaters may comprise an metal heater plate, such as an aluminium heater plate bearing a plasma electrolytic oxide (PEO) coating of aluminium oxide. A heater element, or track, may be screen printed on the surface of the PEO layer to form an electrode. A temperature sensing device, such as a thermistor, may then be fixed to the heater. The thermistor may be a printed or surface mounted device for example.

(24) FIG. 6 shows a block diagram of a first embodiment 60 of a hair styling appliance with a modified power supply and control system. In this embodiment, the power supply 65 is housed in an external unit 61. The external power supply is capable of delivering 120 W at between 12V and 24V. The power supply output connects via a 2-core cable 62 to the hand-held tongs 63. The external power supply rectifies the AC input to provide a DC output the tongs. Operating at 12V, the 2-core cable is chosen to handle approximately 8-9 A.

(25) In the embodiment of FIG. 6 the power supply is housed externally, with the components for controlling the heaters are housed in the body on of the tongs. In the hand-held tongs, the heater controller/control electronics 66 drive a power controller and transistor 67 which in turn switches in a current to the heaters 681, 691 to heat the heatable plates. A thermistor 682, 692 on each heater plate allows the temperature of each heater plate to be monitored independently. Independent control of each heater may then be possible.

(26) One advantage of this arrangement is that the cable connecting the external unit to the hand-held tongs only requires two cores, meaning that the cable assembly is both low cost and also lightweight.

(27) FIG. 7 shows a block diagram of a second embodiment of a hair styling appliance with a modified power supply and control system. In this embodiment, the power supply 75 is housed in an external unit 71 along with the heater controller/control electronics 76 and power transistor drive 77 for driving the heaters. The external power and control unit is connected to the hand-held tongs 73 by a four-core cable. Two cable cores provide power to the heaters 781, 791, and another two cores are connected to a thermistor 782 for sensing the temperature of heater 781.

(28) In the hand-held tongs, the two heaters 781, 791 are connected in parallel, with the thermistor 782 mounted to one of the heater/heatable plate assemblies. Both heaters are controlled together. One advantage of this arrangement is that there is a reduction in components in the hand-held tongs, with power supply and control components moved into the external unit. Furthermore, only a four-core cable is required, meaning that the cable is still relatively lightweight and low cost.

(29) In the embodiment shown in FIG. 7, the power supply typically generates an output of approximately 12V to drive the parallel connected heaters. In a variant, the heaters may be connected in series, with the power supply generating an output of around 24V. In this way, the current requirement would be halved meaning that thinner gauge cable cores may be used to power the heaters.

(30) Turning now to FIG. 8, this shows a variant of the FIG. 7 embodiment. In this embodiment, the power supply 85 is also housed in an external unit 81 with the heater controller/control electronics 86 and power transistor drive 87 for driving the heaters. This embodiment differs to FIG. 7 by providing independent sensing and control of each heater 881,891. Two thermistors 882, 892, one for each heater plate, sense the temperature of each heater plate in the hand-held tongs. The temperature sense signals from each thermistor are fed back to the control electronics in the external unit.

(31) In the embodiment in FIG. 8 a six-core cable 82 is used. Three cores provide power to the heaters, one of which provides a switched drive signal for one heater, another provides a switched drive signal for the other heater, and the third provides a shared return path. The further three cores are used for the thermistors, with one shared wire, and the remaining two each connected to a different one of the thermistors to provide separate temperature sense signals. Each thermistor may then be used in one of the many known thermistor circuits, such as a bridge circuit for example, allowing the sense signal from each thermistor to be used to determine the temperature of the heater plate on which the thermistor is positioned.

(32) In the embodiments shown in FIGS. 7 and 8, the resulting hand-held tongs may comprise of a body with two arms, each bearing a hair styling heater, and so may be lightweight. With the power supply and heater control housed externally, embodiments are permitted that comprise only electrical wires providing a connection between the external power supply and the heaters within the body of the hand-held tongs.

(33) As explained previously with reference to FIG. 3, in conventional styling apparatus the power supply module 22 may incorporate a feedback loop to control and adjust the voltage output of the power supply under different loads. The heater control unit may further include a feedback loop from the thermistor back to the processing element to sense and adjust power being delivered to the heater plates. FIGS. 9a and 9b show one way of combining the separate power supply and heater control module to achieve a more compact design.

(34) FIG. 9a shows a modified version of the power supply and control modules shown in FIG. 3. In FIG. 9a, the secondary side of the transformer 223 is connected to the heater plates 26, rather than to the separate heater control unit. Modules that may now be removed are shown in dotted lines on FIG. 9a. The two feedback loops are now replaced by a feedback loop 229 from the temperature sensor to a modified power supply controller 222. A further feedback loop may be provided from each temperature sensor to the modified power controller.

(35) The removal of several modules means that the more compact circuit of FIG. 9b is formed. As shown in FIG. 9a, modules such as rectification and voltage feedback in the power supply may no longer be needed, as well as the local PSU, processing element and power control modules in the heater control unit. Heater control functionality may now be incorporated into the modified power controller.

(36) Shown in FIG. 9b, the secondary side of the transformer now feeds the heater elements in the heater plates via connection 227. No rectification is required, but may be provided in some embodiments if it is preferred to drive the heater elements/heater plates with a DC power source.

(37) The temperature sensor feeds a temperature sense signal 229 to the modified power controller 922. The power controller is accordingly reconfigured to control the output voltage on the secondary side in response to the sensed temperature, i.e. the output voltage on the secondary side of the transformer winding is now dependent upon the sensed temperature. This eliminates the need for a separate heater control to separately provide thermal control of the heaters. This way, the power supply is regulated by means of the temperature sense signal, rather than monitoring the output voltage.

(38) As the skilled person will appreciate, galvanic isolation is typically a requirement in such systems to provide electrical isolation from the mains electricity. In the modified electronics of FIG. 9b the temperature sensor may be coupled to the modified power supply controller 922 on the primary side of transformer 923 and inherently isolated from the secondary side of the transformer as there is no electrically conductive connection to the heater platesonly a thermal connection. In this way, no opto-isolator may be needed.

(39) FIG. 9c shows an illustrative schematic of a switched mode power supply (SMPS) for a hair styling apparatus. The SMPS in this illustrative embodiment is in a flyback configuration with control electronics using temperature sense feedback. In variants it will be appreciated that other SMPS configurations may be used, such as a forward converter or full forward converter, again with temperature sense feedback from a temperature sensor sensing a temperature of a hair styling heater. An AC mains input 959 is coupled to rectifier circuit 951. Reservoir capacitor 958 is connected across the primary side of the transformer 923 and switching transistor 957. The secondary side of the transformer 923 is then coupled to the heater element 956 in a heater plate.

(40) Feedback is provided by a temperature sensor 954 which feeds a temperature sense signal to the modified power supply controller 952 on the primary side of the transformer.

(41) In many conventional power supply systems a feedback signal is provided from the output voltage signal. To retain the isolation between primary and secondary sides of the transformer 923, isolation means, such as an opto-isolator may be used. However in the embodiment of FIG. 9c the temperature sensor itself is electrically isolated from the secondary side circuit of the combined power supply and heater circuit as indicated by arrow 955 in FIG. 9c. This means that no further isolation may be necessary as the temperature sensor may be inherently isolated from the secondary side of the transformer.

(42) This temperature sense signal may then be used to control the duty cycle of the switching transistor 957 responsive to the sensed temperature so as to adjust the output (e.g. voltage) on the secondary side of the transformer and accordingly the power to the heater element.

(43) Increasing the duty cycle, i.e. turning the transistor switch on for a longer percentage of the switching period may then lead to an increased output voltage. Conversely, reducing the duty cycle may then lead to a reduced output voltage. Optionally, smoothing/rectifying components may be added to the secondary side of the transformer, including a diode and output smoothing capacitor, although it will be appreciated that for driving a heating element these may not be essential.

(44) The temperature sensor provides feedback to the modified power supply controller. The controller may then, for example, compare the sensed signal with a reference voltage for the normal operating temperature.

(45) Rather than controlling the output to provide a constant voltage, the controller, now dependent on a temperature sense signal, may be configured to control the output to provide a constant output temperature, or adjust as necessary. This may lead, for example, to the voltage on the secondary side varying, or limiting the current drive.

(46) In another embodiment, the output may be controlled to switch between powering the heater, i.e. drive (on), and not driving the heater, i.e. no-drive (off), enabling the output to drive the heater only when the temperature is below a desired operating temperature. In such an embodiment, in periods when the heater plates are being driven the secondary side voltage may be, for example, 12V. In periods when the heater plates do not need to be driven, the secondary side may not be driven, i.e. 0V. In such an embodiment, if the sensed value is below a reference value for the normal operating temperature, the resulting signal from a comparison of the reference value and sensed value may be used as an indicator that the secondary side now needs to be driven, i.e. the comparison signal may be considered a call for heat signal. When the desired operating temperature is reached, then the call for heat is disabled meaning that the secondary side no longer needs to be driven.

(47) In an SMPS the duty cycle of the switching transistor 957 may be controlled dependent on the temperature sense signal to either increase or decrease the secondary side voltage and thus the voltage delivered to the heating element. In variants, the switching frequency may also be controlled.

(48) The controller may be further configured to limit the maximum current transferred from the primary side to the secondary side of the transformer.

(49) In the event that the sensed temperature becomes excessive, the modified power supply controller may completely disable the switching transistor such that no power is transferred to the second side at all, meaning that the heaters are promptly turned off.

(50) The modified controller may also incorporate additional features, such as a temperature control. This optional temperature control may allow a user to adjust a temperature of the hair styling heater(s) and may be located at the power supply and/or appliance end of the link, for example to adjust the temperature by modifying the temperature sense signal and/or the response (of the power supply) to the signal. The modified power supply controller may incorporate such functionality.

(51) It will be appreciated that the schematic in FIG. 9c is an illustrative example only and further components may well be includedthe intention is to show feedback from the temperature sensor, providing inherent galvanic isolation in the feedback loop, sensing the temperature of the heater plates to the modified power supply controller.

(52) In the embodiment of FIG. 9c a thermistor is used, however it will be appreciated that there are many other forms of temperature sensor that may be used to detect a change in temperature, including thermocouples, resistive elements, and shape memory materials such as bi-metallic strips. In the latter case, a shape memory material may be used, for example, to detect that a temperature threshold has been crossed, activating or deactivating one or switches to generate one or more temperature sense signals to feedback to the modified power supply controller.

(53) The resulting combined power and control module has a reduced component count compared to the conventional separate power supply and heater control modules, with feedback from the heater plate temperature sensor (a thermistor in the embodiments shown) back to the power controller. Thus, the voltage delivered by the power conversion is controlled dependent on the sensed temperature feedback.

(54) In other embodiments, additional temperature sense signals may be fed back from additional temperature sensors monitoring other heating plate and/or monitoring other zones on the same heating plate. The latter enables a heating plate on one arm to be divided into multiply independent and controllable heating zones, either along the length or across the width of the heating plate.

(55) FIGS. 10a-c show three variants of the hair styling apparatus incorporating the combined power and control module of FIG. 9b. In all three variants the temperature sensor may provide the inherent galvanic isolation in the feedback loop between the primary and secondary sides of the transformer.

(56) FIG. 10a shows a modified version of the styling apparatus in FIG. 6, with an embodiment 100 of the hair styling apparatus housing the combined power supply and heater control module 106 in the hand-held housing 104 of the styling apparatus. In FIG. 10a, the styling apparatus is connected to a mains AC connection via a conventional two-core cable (or three-core if a ground connection is required) without use of an external unit to house any power supply or heater control components. However, the use of the combined power and heater control module, with feedback from the temperature sensor to the power supply switching control means that the component count is reduced, the weight is reduced, and the space required to house the electronics is reduced compared to a hair styling apparatus implementing a conventional power supply and control system.

(57) FIG. 10b shows a modified version of the styling apparatus of FIG. 7, with an embodiment 110 of the hair styling apparatus housing the combined power and control module in an external unit 112. In this embodiment the thermistor senses the temperature of one heating plate, which is then fed back to the combined power and control module to control the drive voltage to both heating plates.

(58) FIG. 10c shows a modified version of the styling apparatus of FIG. 8, with an embodiment 120 of the hair styling apparatus housing the combined power and control module in an external unit 122. In this embodiment one thermistor is used to sense the temperature of each heating plate, with both sense signal fed back to the external unit 122 housing the combined power and control unit 126. Each heater may then be controlled independently.

(59) In the embodiments shown in FIGS. 10b and 10c, as with the embodiments shown in FIGS. 7 and 8, the resulting hand-held tongs may comprise a body with two arms, each bearing a hair styling heater, and so may be lightweight. With the power supply and heater control housed externally, embodiments are permitted that comprise only electrical wires providing a connection between the external power supply and the heaters within the body of the hand-held tongs. Furthermore, in the embodiments in 10b and 10c, the size and weight of the external power supply unit may be significantly reduced over the embodiments shown in FIGS. 7 and 9 owing to the reduction in component count by way of feeding back the temperature sense signal to the power controller.

(60) In the previously described embodiments that incorporate the heater control into the external housing, for example as shown in FIGS. 7, 8, 10c and 10c the return path from the temperature sensor may be provided as one or more wires separate to those powering the hair styling heaters, for example for isolation. Alternatively a feedback signal may be carried by one or more wires carrying power to the heater, for example as a signal modulated into the power supply at the hand-held tongs end of the link (and demodulated at the power supply end). This can reduce the number of wires used for the link, meaning that, for example, a four or six core wire may be reduced to a two core cable to provide power to the handheld tongs and modulated feedback on the same wires.

(61) In variants of the embodiments shown in FIGS. 10a-10c incorporating the circuit of FIG. 9b, further functionality may be added to provide a user interface, enabling user control of the heater plate temperatures, visual and audio feedback, and also to provide calibration capabilities for the temperature sensors uses. In some variants such functionality may be incorporated into the combined power and control module, in others a separate processing element (microcontroller, PIC or the like) may be used. Should any features be incorporated into the handheld tongs, signals back to the external unit may again be returned in similar ways to the temperature sense feedback.

(62) No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

(63) Through out the description and claims of this specification, the words comprise and contain and variations of the words, for example comprising and comprise, means including but not limited to, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

(64) Throughout the description and claims, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

(65) Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example, of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.