GB2475854A

GB2475854A - Mains lead switching off on disconnection

Info

Publication number: GB2475854A
Application number: GB0921087A
Authority: GB
Inventors: Sanowar Hussain Khan
Original assignee: City University of London
Current assignee: City University of London
Priority date: 2009-12-02
Filing date: 2009-12-02
Publication date: 2011-06-08
Also published as: WO2011067322A1; GB0921087D0

Abstract

A power coupling comprises a first connector 15 for plugging into a mains power supply outlet, a second connector 29 for plugging into an electrical appliance 3, and a switch module 27 to automatically break an electrical connection between the first connector and the second connector in the event that said second connector is unplugged from the appliance. This may prevent power being wasted in a transformer 7 or charging circuit 25, or may make a kettle lead safe when not in use.

Description

POWER COUPLING

Field of the Invention

This invention relates to a power coupling for an electrical appliance, particularly but not exclusively to a power coupling that is suitable for coupling a portable appliance such as a mobile telephone, personal digital assistant (PDA) or portable music player (such as an iPod or other digital music player) to a mains power supply.

In one illustrative embodiment the power coupling is embodied as a battery charger (for example, a charger for a mobile telephone or a portable digital music player), and in another as a power cord for an electrical appliance (such as a power cord with a three-pin plug at one end, and a kettle plug at the other end); and in yet another as a power supply unit for an electrical appliance (such as a power supply for a laptop computer).

Background to the Invention

It is commonplace for electrical appliances (particularly portable electrical appliances) to be powered by means of a battery pack, and these battery packs need recharging from time to time. For example, in the context of a mobile telephone, it is normal for the phone to include a battery pack, and for that pack to be rechargeable by coupling the phone to the mains power supply with a suitable battery charger.

Such battery chargers typically include a transformer (which may be of an air-core (i.e. coreless) design or a more conventional solid-core design), a power inlet for coupling to the mains power supply socket (typically with a two-or three-pin plug on one end), and a lower voltage power outlet for coupling to a mobile telephone to enable the battery within the phone to be charged.

It is well established that battery chargers of this type are less than 100% efficient (typically much less than 100% efficient) and will consume energy in use. It is less well known, however, that such chargers will consume energy (if the mains socket is switched on) even if the low voltage charger outlet is not connected to a battery pack that needs charging, and as a result it is commonplace for such chargers to be left switched on even when they are not connected to a battery pack that needs charging.

Whilst the amount of energy consumed by any one charger is trivial, the cumulative power loss of many chargers can be significant.

To address such problems it has previously been proposed, for example as disclosed in GB2443455, to incorporate electronic circuitry within a battery charger, which circuitry is configured to detect when a load is connected to the charger outlet, and decouple the charger from the power supply (in this instance by means of a relay) in the event that no load is detected.

Whilst this arrangement seems to address the above-described problem, a significant drawback is that the device described necessarily requires two additional power consuming components to function -namely, a capacitor and a rechargeable internal battery. The additional circuitry of this device introduces additional costs, as well as additional components that may malfunction. Another drawback is that the inclusion of additional components necessarily increases the size of the charger.

The abovementioned problem also applies to power supply units, for example those used to power portable equipment such as a portable or laptop computer. Such power supply units comprise a power inlet for coupling to the mains power supply socket (typically with a two-or three-pin plug on one end), a lower voltage power outlet for coupling to the device to be powered, and a transformer module configured to step down mains voltage to the voltage appropriate for the device being powered. As will be appreciated, if the device to be powered includes a battery or battery pack, then the power supply unit may additionally function as a battery charger.

As with the aforementioned battery charger, the transformer of such a power supply unit will consume electricity even if unconnected to a device to be powered, and whilst the amount of power consumed by any one power supply unit is small, the cumulative loss is significant.

In the context of power cords for electrical appliances, such as a kettle lead for example, the problem to be addressed is not one of power consumption (because such cords do not typically comprise a transformer and hence do not consume power if left plugged into a switched-on mains socket), but safety.

Specifically, it will be appreciated that when a power cord is plugged into a switched-on mains socket at one end, and the other end of the power cord is not plugged into an appliance then that free end (the "appliance end") of the power cord will be live and an accident could occur if contacts within the cord were to be bridged.

Although it is commonplace for the appliance end of a power cord to be protected (for example by encasing the appliance end in a rubber moulding that obstructs access to the live components of the cord) there is still the potential for accidents to occur.

The present invention has been devised with the foregoing problems in mind.

Summary of the Invention

In accordance with a presently preferred embodiment of the present invention, there is provided a power coupling comprising: a first connector configured for plugging into a mains power supply outlet; a second connector for configured for plugging into an electrical appliance, and a switch module configured to automatically break an electrical connection between said first connector and said second connector in the event that said second connector is unplugged from said electrical appliance.

In a particularly preferred arrangement, said switch module is configured to automatically make an electrical connection between said first connector and said second connector in the event that said second connector is plugged into an electrical appliance.

In one envisaged arrangement the switch module may comprise a switch and an actuator, said actuator being moveable to close said switch and make said electrical connection. The actuator may close said switch by urging a first contact of said switch into electrical contact with a second contact of said switch.

In another envisaged arrangement, the switch module may comprise an actuator that is moveable to bridge first and second spaced electrical contacts and thereby make said electrical connection.

Preferably the actuator is moveable against a resilient bias.

The resilient bias may be configured to drive said actuator away from said first contact, to thereby allow said first contact to move away from said second contact to break said electrical connection. In another arrangement, the resilient bias may be configured to drive said actuator away from said spaced electrical contracts to break said electrical connection as said second connector is unplugged from said electrical appliance.

In a preferred arrangement, the actuator is configured to move as said second connector is plugged into an electrical appliance. For example a part of said appliance may bear on said actuator as the second connector is plugged into the appliance to move said actuator.

In one arrangement the actuator may project from said second connector of said power coupling when said second connector is unplugged from said appliance.

The second connector may comprise a housing and a plurality of electrical contacts for coupling with corresponding contacts of an electrical appliance. The actuator may be driven into the housing when said second connector is plugged into an appliance. In envisaged implementations, at least part of said actuator is electrically non-conducting.

In one embodiment the coupling is configured as a power supply unit and includes a transformer that is operable to step-down a mains supply voltage at said first connector to a lower appliance voltage at said second connector. In another embodiment the coupling is configured as a battery charger and includes: a transformer that is operable to step-down a mains supply voltage at said first connector to a lower appliance voltage at said second connector, and battery charging circuitry.

In preferred embodiments, the transformer includes primary and secondary windings, and said switch module is configured to be capable of interrupting the supply of power to said primary winding.

In a particularly preferred arrangement, an embodiment of the present invention provides a power coupling comprising: a first connector configured for plugging into a mains power supply outlet; a second connector for configured for plugging into an electrical appliance, electronic circuitry that is electrically coupled between said first and second connectors and consumes electrical power when energised, and a switch module configured to automatically break an electrical connection between said first connector and said electronic circuitry in the event that said second connector is unplugged from said electrical appliance.

In another embodiment, there is provided a power coupling comprising: a first connector configured for plugging into a mains power supply outlet; a second connector for configured for plugging into an electrical appliance, and a switch module that is at least partly embedded within said second connector, said switch module being configured to automatically break an electrical connection between said first connector and said second connector in the event that said second connector is unplugged from said electrical appliance.

Other features, embodiments and advantages of the teachings of the invention are set out hereafter.

Brief Descri�tion of the Drawings Various aspects of the teachings of the present invention, and arrangements embodying those teachings, will hereafter be described by way of illustrative example with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of a prior art battery charger; Fig. 2 is a circuit diagram showing the components of the prior art charger shown in Fig. 1; Fig. 3 is a schematic representation of a power coupling according to an embodiment of the present invention; Figs. 4 to 7 are schematic representations of illustrative second connectors for use with power couplings according to embodiments of the present invention; Fig. 8 is a schematic representation of a power coupling according to another embodiment of the present invention; and Fig. 9 is a schematic representation of a power coupling according to yet another embodiment of the present invention.

Detailed Descri�tion of Preferred Embodiments Referring now to Figs. 1 and 2, there is shown in Fig. 1 a schematic representation of a power coupling in the form of a conventional battery charger 1. In this illustrative arrangement the charger 1 is configured for charging a battery pack of a mobile telephone 3.

The charger 1 comprises a transformer module 5 that contains a transformer 7 (with primary 7(i) and secondary 7(u) windings), LED5 9 and battery charging control circuitry 11. The transformer module 5 is coupled by a cable 13 to a first connector 15 that (in this embodiment) comprises a three-pin plug which can be plugged into a complementary mains power outlet 17. The transformer module is coupled by a second cable 19 to a second connector 21 that is suitable for plugging into a socket on the mobile telephone 3.

When the first connector 15 is plugged into the socket 17, power is supplied to the transformer module 5 (for example at 240V) and the transformer acts to step-down that supply voltage to a lower voltage (for example 5 or 9 volts) that is suitable for recharging the battery of the mobile telephone 3. As described earlier, if the second connector should be unplugged from the telephone 3, power will be supplied to the primary coil 7(i) of the transformer whilst the first connector 15 is plugged into the socket 17 and the socket 17 is switched-on, and even though the telephone 3 has been decoupled some of that power will be lost.

Referring now to Fig. 3, there is depicted a power coupling 23 according to an embodiment of the invention -the coupling being configured in this instance as a battery charger.

The power coupling 23 of this embodiment comprises, in addition to conventional battery charging circuitry 25, a switch module 27 that is configured to be capable of interrupting the supply of power from the first connector 15 to the second connector 29.

In the preferred arrangement the switch module 27 forms an integral part of the second connector 29.

As shown in Fig. 3 the switch module is coupled between the first connector 15 and the primary winding 7(i) of the transformer 7. In one envisaged arrangement the switch module 27 is configured to operate automatically to interrupt the supply of power from the first connector to the primary winding 7(i) of the transformer 7 when the second connector 29 is decoupled from an electrical appliance (in this instance, the telephone 3). As a result, when the second connector 29 of this power coupling 23 is unplugged from the electrical appliance 3, the transformer 7 is isolated from the mains electricity supply, and as a consequence no energy is consumed by the transformer and the coupling as a whole.

In this envisaged arrangement, the switch module 27 is also configured to operate automatically to electrically couple the first connector 15 to the primary winding 7(i) of the transformer 7 when the second connector is plugged into an electrical appliance, in this instance the mobile telephone 3.

Envisaged configurations for a 2nd connecter with an integrated switch module 27 are shown in Figs. 4 to 7 and will now be described, but it will be appreciated by persons skilled in the art that the configurations shown are merely illustrative and that many other configurations could be devised to interrupt the electrical connection between the first connector 15 and transformer 7.

Referring now to Fig. 4, in this arrangement the second connector 29 includes a conventional connector interface 33 that is electrically wired (n.b. the wiring is not shown in Fig. 4) to the battery charging circuitry 25 and is configured to mate with a complementary connector on the telephone 3 (for example for the supply of electrical power to a battery in the telephone 3).

The connector 29 also includes a first contact 35 that is electrically coupled to the first connector 15, and a second contact 37 that is electrically coupled to the primary winding 7(i) of the transformer 7. An actuator 39 having a shaft 41 and a cap 43 is mounted within the connector 29 and is moveable against a resilient bias 45 between the position shown in Fig. 4 and a position where the shaft projects between and bridges the first 35 and second 37 contacts. In the preferred arrangement at least the shaft 41 is electrically conducting so that when the actuator moves to a position where the shaft 41 bridges the first and second contacts 35, 37 an electrical connection is made between the 1t connector 15 and the primary winding 7(i) of the transformer 7.

In the preferred arrangement the actuator 39 is arranged within the connector 29 so that on plugging the connector 29 into the telephone, a part of the telephone 3 bears on the cap 43 of the actuator to drive the actuator against the resilient bias 45 to the position aforementioned where the shaft 41 electrically bridges the first and second contacts 35, 37. When the connector is unplugged from the telephone, the resilient bias drives the actuator back to the position indicated in Fig. 4, thereby breaking the electrical connection between the first and second contacts 35, 37 and the shaft 41, and decoupling the transformer 7 from the first connector 15.

Referring now to Fig. 5 of the drawings, in this arrangement a switch 47 is provided between the first and second contacts, and the actuator is moveable to close the switch to complete the electrical circuit between the first connector 15 and transformer 7. In the preferred arrangement the switch 47 is biased so as to be normally open (that is to say, to be open when not being driven closed by the actuator), for example by forming one part of the switch (the part on which the actuator bears to close the switch) from sprung metal, such as sprung copper. As will be appreciated by persons skilled in the art, since the actuator 39 does not carry a current in this configuration, it can be formed of an electrically insulating material.

Referring now to Fig. 6 of the drawings, the connector configuration in this arrangement is the same as that shown in Fig. 4 except that in this arrangement the actuator projects from the second connector 29 instead of being recessed within a cowl 29(i), as is normal for connectors 29 of this type.

In the arrangement shown in Fig. 7, the first and second contacts 35, 37 are spaced from one another, and the actuator 39 is provided with an electrically conducting plate 48 at one end thereof that can be brought to bear on the first and second contacts to complete the circuit between the first connector 15 and the transformer 7. In this instance the cap and rod of the actuator may be formed of insulating material.

Referring now to Fig. 8, there is depicted a power coupling 49 in accordance with an embodiment of the present invention that is configured as a power supply unit. The coupling 49 includes a transformer 7, first and second connectors 15, 29 and a switch module 27. Such a coupling may be used, for example, to power childrens' toys, such as slot car racing sets in a safer manner than is currently possible with existing low voltage power supply units.

Referring now to Fig. 9, there is depicted a power coupling 51 in accordance with another embodiment of the present invention. In this instance the coupling is configured as a power cord (for example of the type that might be used to couple a desktop computer to a mains power outlet), and by embodying the teachings of the present invention it is possible to avoid situations where a mains voltage is accessible via a second connector that has been unplugged from an item of equipment.

It will be appreciated from the foregoing that the teachings of the present invention improve safety, and enable power losses associated with conventional power couplings to be avoided.

It will also be appreciated that whilst various aspects and embodiments of the present invention have heretofore been described, the scope of the present invention is not limited to the particular arrangements set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the scope of the appended claims.

For example, whilst the first connector has been described herein as being a three-pin plug (suitable for connection to a standard UK plug socket), it will be appreciated that connectors of the type used in continental Europe or the USA could be used instead. It will also be appreciated that the teachings of the invention are not solely applicable to power couplings for portable appliances, but may additionally or alternatively be applied to power couplings for fixed appliances.

It should also be noted that whilst the accompanying claims set out particular combinations of features described herein, the scope of the present invention is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features herein disclosed.

Claims

CLAIMS1. A power coupling comprising: a first connector configured for plugging into a mains power supply outlet; a second connector configured for plugging into an electrical appliance, and a switch module configured to automatically break an electrical connection between said first connector and said second connector in the event that said second connector is unplugged from said electrical appliance.
2. A coupling according to Claim 1, wherein said switch module is configured to automatically make an electrical connection between said first connector and said second connector in the event that said second connector is plugged into an electrical appliance.
3. A coupling according to Claim 2, wherein said switch module comprises a switch and an actuator, said actuator being moveable to close said switch and make said electrical connection.
4. A coupling according to Claim 3, wherein said actuator closes said switch by urging a first contact of said switch into electrical contact with a second contact of said switch.
5. A coupling according to Claim 1 or 2, wherein said switch module comprises an actuator that is moveable to bridge first and second spaced electrical contacts and thereby make said electrical connection.
6. A coupling according to any of Claims 3 to 5, wherein said actuator is moveable against a resilient bias.
7. A coupling according to Claim 6 when dependent on Claim 4, wherein said resilient bias is configured to drive said actuator away from said first contact, to thereby allow said first contact to move away from said second contact to break said electrical connection.
8. A coupling according to Claim 6 when dependent on Claim 5, wherein said resilient bias is configured to drive said actuator away from said spaced electrical contracts to break said electrical connection as said second connector is unplugged from said electrical appliance.
9. A coupling according to any of Claims 3 to 8, wherein said actuator is configured to move as said second connector is plugged into an electrical appliance.
10. A coupling according to Claim 9, wherein a part of said appliance bears on said actuator as the second connector is plugged into the appliance to move said actuator.
11. A coupling according to Claim 9 or 10, wherein said actuator projects from said second connector of said power coupling when said second connector is unplugged from said appliance.
12. A coupling according to any of claims 3 to 11, wherein said second connector comprises a housing and a plurality of electrical contacts for coupling with corresponding contacts of an electrical appliance.
13. A coupling according to Claim 12, wherein said actuator is driven into the housing when said second connector is plugged into an appliance.
14. A coupling according to any of Claims 3 to 13, wherein at least part of said actuator is electrically non-conducting.
15. A coupling according to any preceding claim, wherein said coupling is configured as a power supply unit and includes a transformer that is operable to step-down a mains supply voltage at said first connector to a lower appliance voltage at said second connector.
16. A coupling according to any of Claims 1 to 14, wherein said coupling is configured as a battery charger and includes: a transformer that is operable to step-down a mains supply voltage at said first connector to a lower appliance voltage at said second connector, and battery charging circuitry.
17. A coupling according to Claim 15 or 16, wherein said transformer includes primary and secondary windings, and said switch module is configured to be capable of interrupting the supply of power to said primary winding.
18. A coupling according to any preceding claim, wherein said first connector comprises a plug for plugging into said mains power supply outlet.
19. A power coupling comprising: a first connector configured for plugging into a mains power supply outlet; a second connector for configured for plugging into an electrical appliance, electronic circuitry that is electrically coupled between said first and second connectors, and a switch module configured to automatically break an electrical connection between said first connector and said electronic circuitry in the event that said second connector is unplugged from said electrical appliance.
20. A power coupling according to Claim 19, wherein said switch module forms part of said second connector.
21. A power coupling according to Claim 19 or 20, wherein said switch module is configured to automatically make the electrical connection between said first connector and said electronic circuitry in the event that said second connector is plugged into an electrical appliance.
22. A power coupling according to any of Claims 19 to 21, wherein said electronic circuitry consumes electrical power when energised, and the decoupling of said circuitry from said first connector reduces the power consumption of said coupling when said second connector is decoupled from an electrical appliance.
23. A power coupling comprising: a first connector configured for plugging into a mains power supply outlet; a second connector for configured for plugging into an electrical appliance, and a switch module that is at least partly incorporated within said second connector, said switch module being configured to automatically break an electrical connection between said first connector and said second connector in the event that said second connector is unplugged from said electrical appliance.
24. A power coupling substantially as herein before described with reference to any of Figs. 3 to 8.