Background of the invention Touch activated lamps are well known. Generally, these lights are operated by touching the base of the lamp, for example. Touching the base, or another part of the light such as a touch pad, activates a switch which operates to turn the light on. In some lamps, repeated touching of the base increases the brightness of the light.

The lamp is also turned off by touching the base. In basic touch lights, one touch turns the light on, the next touch turns the light off.

The need to manually touch the light in order to turn it off, causes difficulties when the light is to be used as a night light, eg. a light to fall asleep by. In this case it is not desirable to have to manually turn the light off and it may not be desirable to leave the light on all night.

Further, a need exists for portable touch activated lights that can be used when mains power is not available, for example, when camping.

It is therefore an object of the invention to provide an electronic circuit for a portable light that removes the need to manually turn the light off.

Summary of the invention The invention provides a power supply circuit for an electrically powered device such as a light, including: switch means adapted to be closed by manual actuation; a capacitor connected to be charged when said switch is closed; and a discharge timing circuit arranged to discharge said capacitor to said electrically powered device over a predetermined time interval after said switch is opened.

Preferably, the discharge circuit timing includes a Darlington, preferably super Darlington, transistor circuit including a power transistor in series with the electrically powered device when the latter is in situ.

Advantageously, the switch means is adapted to be touch activated, eg. activated by contact with a touch pad or by resistive touch across a pair of terminals.

The switch means preferably further includes a transistor triggered silicon controlled rectifier.

Preferably, the electrically powered device is an electric lamp. The circuit and lamp are advantageously provided in a portable light which may typically have its own power supply, eg. battery means.

Means is advantageously provided to vary said predetermined time interval.

The invention also provides a portable, touch-activated light which includes a power supply circuit that supplies electrical power to said light, the power supply circuit being adapted such that power supplied to said light gradually diminishes and ceases over a predetermined time interval.

Advantageously, the portable, touch-activated light includes a power supply circuit according to the first aspect of the invention.

The invention further provides a portable light, which includes switch means, that are activated by contact with a touch pad or by resistive touch across a pair of terminals, which enables a user to activate said switch means by placing a part of the body on the light without the need to expressly locate the switch means.

Preferably said light is contoured and sized so that when a user's hand is placed on said light, the user's hand follows the contours of said light, thereby directing the users hand to said touch activated switch means.

Preferably the light is substantially dome shaped and the touch pad or touch terminals are elongated to the extent that it is unlikely that a user can place their hand on the light in the manner described without contacting the switch means.

In one embodiment the touch activated switch means are a strip or plurality of strips which encircle the perimeter of the device providing a large and easily accessible switch means.

Brief description of the drawings The invention will now be described by way of a non-limitative example with reference to the accompanying drawings in which: Figure 1 is a circuit diagram of an embodiment of the invention; Figure 2 is a circuit diagram of an alternative embodiment of the invention; Figure 3 is a side elevation view of a light embodying the invention; Figure 4 is a top plan view of the light shown in figure 3; Figure 5 is a perspective view of the light shown in figure 3; Figure 6 is a side elevation view of a light being an alternative embodiment of the invention; Figure 7 is a top plan view of the light shown in figure 6; Figure 8 is a perspective view of the light shown in figure 6.

Detailed description of the embodiments With reference to Figure 1, transistor TR1 and silicon controlled rectifier SCR1 cooperate with a touch pad T/P to form a switch in series with capacitor Cl across a DC power supply which would typically be a battery or set of batteries. The switch is activated by using a finger or body part to touch or hold a touch pad T/P, which is connected between the positive line and the base of transistor TR1.

Capacitor Cl and either of selectable resistors R2 and R3, forms a RC timing element of a discharge timing circuit by which capacitor Cl discharges to a light bulb Ll. The discharge timing circuit includes a super Darlington transistor amplifier circuit. The super Darlington amplifier is a cascade of three transistors TR2, TR3, TR4 in which each collector is connected to the positive rail voltage. The capacitor discharge is connected to the base of TR2, while the emitters of TR2 and TR3 are coupled to the bases of TR3 and TR4 respectively. Transistor TR4 is a power transistor in series with light bulb LI across the DC terminals. Transistor TR4 should be chosen to handle the full load current of light bulb LI.

As mentioned, power is supplied by one or more batteries. When not in use, the circuit power consumption is negligible.

Circuit Operation In order to activate the light bulb, touch pad T/P is touched, thereby closing the switch.

Touch pad T/P activates transistor TR1, which in turn activates SCR1. Rail voltage is thereupon supplied to capacitor Cl via SCR1. SCR1 remains in conduction mode until capacitor Cl is fully charged, at which time SCR1 turns off.

Capacitor Cl is fully charged very quickly since it is essentially in short circuit across the supply rail voltage via SCR1.

With the supply turned off to capacitor C 1, and the capacitor fully charged, capacitor Cl now discharges, via either resistor R2 or R3, to the super Darlington amplifier, (transistors TR2, TR3 and TR4). The stored charge in capacitor Cl gradually decays through the selected timing resistor (R2 or R3) and the super Darlington amplifier. As a result, the light bulb LI also diminishes in intensity until it is extinguished.

It will be appreciated that this circuit eliminates the need to manually turn off the light thereby saving valuable battery power since the light cannot be accidentally left turned on. This is particularly advantageous when the light is being used when camping, for example.

Touching the touch pad T/P causes the cycle to start again. Holding the touch pad T/P causes the light to remain on until the touch pad T/P is open circuited by the removal of the finger (s) or hand. This allows the user to use the device as a low powered torch, for example.

A resistor Rl across the touch pad is only required should the sensitivity be too low. It is recommended that a transistor with a high hfe be used for transistors TR1 and TR2.

Resistor R4 is provided in parallel with capacitor Cl to ensure full discharge of capacitor Cl, and to thereby improve the timing circuit operation.

Resistors RI and R4 are high resistance resistors approx 20 to 30 Mega ohm in value.

All resistors can be either 1/8 or 1/4 watt in power rating.

A heat sink may be required for power transistor TR4; this will depend upon the type of transistor used and size of light bulb LI.

An alternative embodiment is illustrated in Figure 2. The layout of the circuit and the components are essentially as shown in Figure 1 with like components shown as such.

In this embodiment, selectable resistors R2 and R3 are connected across capacitor C 1.

Resistor R 1 in combination with capacitor Cl forms a RC timing element of a discharge timing circuit by which capacitor C1 discharges to light bulb LI.

Selectable resistors R2 and R3 are high resistance resistors respectively of 10 and 20 Mega ohm in value and 1/8 watt in power rating. Resistors R2 and R3 serve not only to ensure full discharge of capacitor C1, but also determine the delay to extinguishment of bulb LI since the time constant of the discharge is influenced by R2/R3.

In the embodiment shown in figures 3 to 5 a portable, touch activated light 30 has a dome shaped casing 32 made of a plastics material which houses the electrical circuit as described above, the touch pads T/P are mounted on the surface of the casing 32. Additionally the casing 32 houses dry cell batteries; a reflector and other components common to portable lighting devices which will be known to a person skilled in the art.

The casing 32 has a opaque lower portion 34 and a translucent or transparent lens portion 36 through which light is dispersed. The dome shaped casing has an upper curved surface, a tapered bottom edge 40 and a generally flat base 42. The base 42 is adapted to allow the night light to rest on a generally flat surface in a stable fashion.

The opaque lower portion 34 of the casing 32 has lobe 46 which rises along the surface of the casing 32 towards the crown 36a of lens 36. Lobe 46 curves into the lens 36 thereby reducing the surface area of lens 36 and positioning the two touchpads T/P closer to the crown 36a. Mounted on lobe 46 are two touch pads T/P which must be bridged by the user to activate the light 30. For reasons which will be explained it is preferable for the touch pads T/P or some part of the touch pads to be near to the crown of the dome.

The touch pads T/P are of an elongated shape and are placed on the lobe such that they are separated by a narrow non-conducting gap with the longest edges of the touch pads T/P parallel to each other and perpendicular to an axis which runs from the crown 36a of the lens 36 outer periphery of casing 32. In use, the worst case scenario is that the user will use their finger to bridge the touch pads T/P whereas the best case is that the user will use their entire hand. As the touch pads T/P are elongated and placed parallel to their longitudinal axis and the gap to be bridged is less than the width/thickness of a child's finger the likelihood of the user bridging the touch pads is increased.

This arrangement of the touch pads T/P in combination with the domed shape of the portable, touch activated light assist the user in being able to activate the touch activated switch means with little effort. The light is contoured or shaped in such a manner to invite the user to place their hand directly over the light to activate it. A user can simply put a relaxed and open hand over the light, contour their hand to the light and contact the touch pads without locating the touch pads T/P or grasping the light. The elongated shape of the touch pads makes it unlikely that the touch pads would lie wholly between the fingers of the user with out making contact with the users fingers.

Children commonly use night lights and for this reason the light should be adapted to be used easily by a child. Children do not necessarily have as well developed coordination as adults and may also lack the patience required to contact both of the touch pads unless it is easy to do so. For this reason the touch pads are relatively large and are placed in an easily accessible position on the surface of the casing. Children also have smaller hands than adults, and since the light is shaped in such a manner to invite the user to place their hand directly over the light to activate it, the touch pads preferably should be placed nearer to the crown of the domed casing than the outer edge. For this reason the touch pads are located on lobe 46.

In a further preferred embodiment show in figures 6 to 8 the portable, touch activated light is similar to the embodiment shown in figures 3 to 5 with the exception that the two touch pads have been replaced by two substantially parallel touch strips T/S which are separated by a narrow. non-conducting gap and encircle the lens portion 36 of the casing 32. By simultaneously touching both touch strips T/S the light is activated.

This embodiment has the advantage that the touch strips T/S can be touched and the light activated from all sides of the light with little effort on behalf of the user. The touch strips preferably follow the contour of the aperture in casing 32 in which the lens 36a sits as well as the contour of the lobe 46. This ensures that some portion of the touch strips T/S are near to the crown 36a of the lens 36 which may assist children in using the portable, touch activated light as described above.

It will be noted that touch pads of any shape or configuration could be utilised to activate the light. Additionally it is also possible for there to be more than 2 touch pads on the surface of the light. An alternative possible arrangement of touchpads includes an array of touch pads substitute sheet (rule 26) RO/AU

separated by non-conducting material that cover a large proportion of the surface of the casing of the light, said touch pads being located on the surface of the casing of the light in such position that by bridging any two adjacent touch pads the circuit is activated. This could be implemented as a series of strips or concentric rings, an array of spots or any other configuration.

It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

The foregoing describes embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto, without departing from the scope of the present invention.

It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

The foregoing describes embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto, without departing from the scope of the present invention.