WO2010015857A1

WO2010015857A1 - Electrical devices with standby mode

Info

Publication number: WO2010015857A1
Application number: PCT/GB2009/050981
Authority: WO
Inventors: Martin James Bellamy
Original assignee: G24 Innovations Limited
Priority date: 2008-08-06
Filing date: 2009-08-05
Publication date: 2010-02-11
Also published as: GB0814409D0

Abstract

The invention relates to the supply of power to electrical devices, such as television receivers or radios, which are operable in both a normal ON mode and a STANDBY mode. As with conventional methods of powering such devices, electric power is supplied to the device from either the mains or a battery when in the ON mode. However, during the STANDBY mode, electric power is supplied to the device from a rechargeable battery which has been charged using the output current of a dye- sensitised photovoltaic cell array which is exposed to ambient light. In the preferred embodiment, the rechargeable battery is used to power the device when two conditions are met: (a) the device is in the STANDBY mode; and (b) there is sufficient charge stored in the rechargeable battery to power the device when in the STANDBY mode.

Description

ELECTRICAL DEVICES WITH STANDBY MODE

The present invention relates to electrically powered devices which are operable in both and ON mode and a STANDBY mode. Such devices include television apparatus, including digital set-top boxes, audiovisual playing and/or recording equipment, such as DVD recorders, portable radios and hi-fi equipment, gaming stations and telephones.

The ON mode is the normal mode of operation in which the device is able to perform its expected functions. The STANDBY mode, sometimes referred to as a "sleep mode", is one in which the device is receptive to an instruction, for example provided by a signal from a remote-control device to operate in its ON mode. Such a conversion is referred to as "waking up", and the ON mode can therefore be referred to as a "wake" mode.

During both the STANDBY and ON modes, electrical power is supplied to the device usually from a mains supply, although in some cases, such as portable radios, this power could be supplied from a battery. During the STANDBY mode, the device consumes significantly less electrical power than when in the ON mode, but this small amount of power is not negligible. Not only are there now a large number of such devices in households throughout the developed world, but the devices are typically retained in their STANDBY mode for the vast majority of the time. As a result of these two factors, the amount of energy consumed by such appliances when in the STANDBY mode is enormous. Indeed, it has been estimated that, in the UK alone, the output of an entire power station is consumed by such devices operating in the STANDBY mode. As will be appreciated, this involves the consumption of a large quantity of scarce natural recourses, such as hydrocarbon fuels. Even when the devices are powered by batteries, it is clearly wasteful, in terms of the greater frequency of replacement of the batteries, and the consequential additional consumption of raw materials used in their manufacture, for additional current to be consumed by battery-powered devices operating in the STANDBY mode.

There are two known methods by which this amount of wasted power can be reduced. The first is to encourage consumers to turn off the devices when not required for a considerable length of time, such as when the consumers are on holiday. The second method is to design the devices such that the amount of electrical power consumed in the STANDBY mode is reduced. However, even with these two methods being applied in practice to some extent, there is still room for a considerable further reduction in the amount of power consumed by such devices in the STANDBY mode.

Thus, in accordance with a first aspect of the present invention there is provided apparatus for use with an electrically powered device which is operable in an ON mode, in which it consumes electrical power at a relatively high rate, and a STANDBY mode, in which it consumes electrical power at a relatively low rate, the apparatus comprising: a photovoltaic transducer arranged to be exposed to ambient light for generating an output electrical current in response thereto; a rechargeable battery arranged to receive as a charging current the output electrical current from the photovoltaic array; means for determining when the device is in the STANDBY mode; and means responsive to the determining means for supplying current from the rechargeable battery to the device only when it is determined that the device is in the STANDBY mode.

By using a photovoltaic transducer to generate the relatively small amounts of electrical power required by the device during its STANDBY mode, the above problem relating to the excessive consumption of mains power or batteries can be overcome.

A photovoltaic transducer responds to incident light by generating a voltage across its terminals which can give rise to an electric current in an external circuit. The term "light" as used throughout this specification is intended to refer not only to visible radiation but also to infrared and ultraviolet radiation. In this way, the energy of the incident light is converted into useful electric energy. The magnitude of the resulting voltage and/or current depends on a number of factors, including the wavelength and intensity of the incident light and the chemical and physical characteristics of the photovoltaic transducer.

Photovoltaic transducers are normally manufactured as an array of photovoltaic cells which are electrically connected together in series, such that the output voltage is the sum of the individual voltages generated across each of the cells. However, since the magnitude of the generated current depends on the area of the light-sensitive surface of the photovoltaic transducer, the photovoltaic cells could alternatively be electrically connected together in parallel so as to increase the effective surface area exposed to the incident light, the effect of which is that, whereas the voltage remains the same as that generated by a single cell, the magnitude of the current generated in an external circuit is increased.

It is now possible to manufacture photovoltaic cells which are connected together in series and in which the length of the cells in the array, and hence the area of light- sensitive surface, is selected such that a desired level of current is generated.

The photovoltaic transducer preferably comprises a dye-sensitised photovoltaic cell array, since such a transducer is capable of generating a useful output current at low levels of ambient light, such as are typically encountered in indoor environments where electrically powered devices are usually installed.

The photovoltaic transducer is furthermore preferably in the form of a flexible sheet, since such a transducer can then readily be attached to the surface of a device while conforming to the surface shape, even if this is curved.

In order for a rechargeable battery to accept the output current from a photovoltaic transducer as a charging current, the level of the output current must be above a first critical value. If the output current is below this value, the battery will not accept any charge, and the output current will simply be wasted. It is only when the output current rises above this critical value, that the battery will accept any charge.

For example, a commercially available NiMH rechargeable battery has a capacity C of 1 250 mAh, and has a critical value of 15 mA below which it will not accept any charging current, assuming that the battery manufacturer's voltage requirements are adhered to.

Although it would be possible to charge a rechargeable battery from the output current of a photovoltaic transducer simply by connecting the output terminals of the photovoltaic transducer directly to the battery terminals, this is not an efficient way of recharging the battery, since, in conditions of low light intensity, such as are normally encountered in an indoor environment, the typical output current of photovoltaic transducers is less than this critical value.

It would therefore be desirable to provide an arrangement which is able to generate a charging current for a rechargeable battery which is always above this critical value. The apparatus therefore preferably also comprises means for accumulating the output electrical current from the photovoltaic transducer when the output electrical current is below a predetermined value and for supplying the charging current to the rechargeable battery at an instantaneous charging rate which is greater than the predetermined value.

The predetermined value is preferably set to be equal or greater than the above critical value, in order to improve the efficiency with which the battery is charged. By accumulating or storing the charge from the photovoltaic transducer until there is sufficient charge to form an efficient charging current for the rechargeable battery, this makes efficient use of the output current of the photovoltaic transducer.

The apparatus preferably also comprises means for determining when the output electrical current is above the threshold value and, in response to a positive determination, for bypassing the accumulating means such that the rechargeable battery is supplied directly with the output electrical current from the photovoltaic transducer. In this way, there is no time delay between the generation of the output current by the photovoltaic transducer and the charging of the battery.

The present invention extends to a method of supplying electrical power to a device which is operable in an ON mode, in which it consumes electrical power at a relatively high rate, and a STANDBY mode, in which it consumes electrical power at a relatively low rate, the method comprising: supplying electrical power to the device from a photovoltaic transducer only during the STANDBY mode; and supplying electrical power to the device from a source other than the photovoltaic transducer during the ON mode.

As indicated above, the source other than the photovoltaic transducer would normally comprise the mains electricity supply but could alternatively, or in addition, comprise a battery. This might be the case, for example, when the device is a portable radio which requires a relatively small amount of power in its ON state.

Since the photovoltaic array might not always be capable of generating sufficient electrical power for the device to function in the STANDBY mode, it is desirable to react to such a condition by arranging for the device to be supplied with power from the same power source as that which supplies power in the ON mode. In this condition, the arrangement for powering the device from the output of the photovoltaic transducer is temporally overridden.

Any electric charge generated by the photovoltaic device when the device is in the ON mode is advantageously stored, e.g. in a capacitor or rechargeable battery, for later use by the device when in the STANDBY mode.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 illustrates a television set with an attached photovoltaic transducer for use in a preferred embodiment of the present invention;

Figure 2 illustrates schematically the apparatus of a preferred embodiment of the present invention;

Figure 3 is a flowchart of the method steps of a preferred embodiment of the present invention;

Figure 4 illustrates in greater detail the charge accumulator circuit of Figure 2;

Figure 5 is a flowchart illustrating the first part of the method of operation of the charge accumulator circuit of Figure 4;

Figure 6 is a flowchart illustrating the second part of the method of operation of the charge accumulator circuit of Figure 4; and

Figure 7 is a graph illustrating the charging and discharging cycles of a capacitor used in the accumulator circuit of Figure 4.

Referring to Figure 1 , a conventional television receiving apparatus 1 is provided with an infrared detector 2 for receiving control signals from a hand-held remote control device (not shown). The television apparatus 1 is operable both in its normal fully functional mode of operation, referred to below as its ON mode, and also in a STANDBY mode in which, although not fully functional, can be made to "wake up" and function in its ON mode by a control signal from the remote control device, or alternatively from a control key (not shown) on the television apparatus 1 itself.

On each of the two upper corners of the television apparatus 1 is a respective photovoltaic transducer 3 comprising a flexible array of dye-sensitised photovoltaic cells which conforms to the underlying surface of the television apparatus 1.

The role played by the photovoltaic transducers 3 in relation to the television apparatus 1 will now be described with reference to Figure 2.

Each photovoltaic transducer 3 generates an output electric current in response to ambient light incident on its surface, and this output current is supplied via a diode 4 to a charge accumulator circuit 5 which stores the electric charge until there is sufficient charge to produce an electric current sufficient to charge the battery 6. The output of the rechargeable battery 6 is connected to a first input terminal of a switch 8, and a mains electric power supply 7 is connected to a second input terminal of the switch 8.

The switch 8 serves to connect either the rechargeable battery 6 or the mains power supply 7 to the television apparatus 1 in dependence on a signal supplied to a control input of the switch 8.

A standby mode selector 9 determines when the television apparatus 1 is in the standby mode, in which case it generates an output signal having a logic level equal to 1.

Furthermore, a voltage comparator 10 determines when the output voltage of the rechargeable battery 6 is sufficient to power the television apparatus 1 in its standby mode, in which case it also generates an output signal having a logic level equal to 1.

The two output signals from the standby mode selector 9 and the voltage comparator 10 are supplied to the two respective inputs of a logical AND gate 1 1 , and the resulting output of the AND gate 11 constitutes a control signal for controlling the operation of the switch 8 such that the television apparatus 1 is powered by the rechargeable battery 6 only if (a) the standby mode is selected and (b) there is sufficient charge stored in the rechargeable battery 6 to power the television apparatus 1 in the standby mode. If neither of these conditions is met, then the switch 8 connects the mains power supply 7 to the television apparatus 1.

The method of operation of the apparatus of Figure 2 will now be described with reference to the flowchart of Figure 3.

A first determination (step 12) is made as to whether the electrically controlled device is in the ON mode or in the STANDBY mode. If it is in the ON mode, then the device is connected to the mains electrical supply (step 13). If the device is in the STANDBY mode, a determination (step 14) is made as to whether there is sufficient charge in the rechargeable battery to power the device. If there is insufficient charge, then the device is again connected to the mains supply. If there is sufficient charge in the battery, then the device is connected to the output of the rechargeable battery (step 15).

The charge accumulator circuit 5 will now be described with reference to Figure 4. The output from the diode 4 is connected to a two-way switch 16 which is controlled by the output of a first voltage comparator 17. The diode 4 serves to prevent any current from flowing back from the battery 6 into the photovoltaic transducer 3 such as might otherwise occur when the battery voltage is greater than the instantaneous output voltage of the photovoltaic transducer 3. The first voltage comparator 17 is supplied at a first input with the output of the photovoltaic transducer 3 and is supplied at a second input with a reference voltage V₁. The output of the first voltage comparator 17 is supplied as a control signal to the two-way switch 16. The first voltage comparator 17 is supplied with power from the rechargeable battery 6 via a suitable connection (not shown). The two-way switch 16 selects one of two possible paths for the output current from the photovoltaic transducer 3, in dependence on the value of the control signal supplied by the first voltage comparator 17. The first path 18 connects the output current to a charge store in the form of a capacitor 19. The second path 20 bypasses the capacitor 19 and supplies the output current directly to the rechargeable battery 6. This arrangement causes the output current from the photovoltaic transducer 3 to be supplied (a) to the capacitor 19 when the level of the output current from the photovoltaic transducer 3 is below the threshold at which any charge can be received by the rechargeable battery 6 and (b) direct to the rechargeable battery 6 when the level of the output current is greater than this threshold. The level of charge in the capacitor 19 at any time is monitored by second and third voltage comparators 21 , 22 which are also powered by the rechargeable battery 6 using suitable connections (not shown). The second voltage comparator 21 is supplied at a first input with a signal representing the voltage across the capacitor 19, and at a second input with a second reference voltage V₂. The third voltage comparator 22 is supplied at a first input with a third reference voltage V₃, which is lower than the second reference voltage V₂, and at a second input with the same signal as is supplied to the first input of the second voltage comparator 21 , representing the voltage across the capacitor 19. The output of the second voltage comparator 21 acts to close a switch 23 in the event that the voltage across the capacitor 19 exceeds the second reference voltage V₂. The switch 23 is connected between the output of the capacitor 19 and the rechargeable battery 6. The output of the third voltage comparator 22 acts to open the switch 23 in the event that the voltage across the capacitor 19 falls below the third reference voltage V₃, thereby terminating the supply of charge from the capacitor to the rechargeable battery 6. The value of the third reference voltage V₃ is selected such that the charging current supplied to the rechargeable battery 6 is always greater than the above-mentioned threshold at which the rechargeable battery 6 starts to accept charge.

The operation of the charge accumulator circuit 5 will now be described with reference to the flowcharts of Figures 5 and 6.

Referring to Figure 5, the output voltage of the photovoltaic transducer 3 is first detected (step 24), and a determination made as to whether or not the output voltage is greater than a first reference voltage V₁ (step 25). If the output voltage is not greater than V₁, then the output current from the photovoltaic transducer 3 is stored in the capacitor 19 (step 26), and the output voltage continues to be monitored (step 24). If, however, the voltage is greater than V₁, then the output current from the photovoltaic transducer 3 is supplied directly to the rechargeable battery 6 (step 27), but the output voltage still continues to be monitored (step 24).

Referring to Figure 6, the voltage across the capacitor 19 is sensed (step 28) and a first determination made as to whether the capacitor voltage is greater than the second reference voltage V₂ (step 29). If the capacitor voltage is not greater than V₂, then the method proceeds to continue sensing the capacitor voltage (step 28). If the capacitor voltage is indeed greater than V₂, then the charge is supplied from the capacitor 19 to the rechargeable battery 6 (step 30). The capacitor voltage is sensed again (step 31 ) and a second determination is made as to whether the capacitor voltage is less than the third reference voltage V₃ (step 32). If the capacitor voltage is not less than V₃, then the method proceeds to continue sensing the capacitor voltage (step 31 ). If the capacitor voltage is indeed less than V₃, then the supply of charge from the capacitor 19 to the rechargeable battery 6 is terminated (step 33), and the method returns to the step of sensing of the capacitor voltage (step 28).

Figure 7 illustrates how the voltage across the capacitor 19 changes with time. At a notional zero time t₀, such as the time at which the photovoltaic transducer 3 is connected to the remainder of the apparatus, or the time at which light starts to be incident on the photovoltaic transducer 3, there is no charge stored in the capacitor 19, and so the voltage across the capacitor 19 is zero.

The level of charge stored in the capacitor 19, and hence also the capacitor voltage, then starts to rise during a first charging regime 34, until a time t-i at which the capacitor voltage reaches the second reference voltage V₂. At this point the capacitor 19 becomes connected to the rechargeable battery 6 so that charge starts to flow out of the capacitor 19 during a discharging regime 35. This is terminated at a time t₂ when the capacitor voltage falls below the third reference voltage V₃, and a further charging regime 36 is initiated which is then terminated again at a time t₃ at which time the capacitor voltage again reaches the second reference voltage V₂. As can be seen from the graph, the duration (t₃ - t₂) of the further charging regime 36 is less than that (ti - t₀) of the first charging regime, since the further charging regime starts at a point where there is still some charge remaining in the capacitor 19, whereas the first charging regime starts when there is no stored charge.

Since the voltage across the capacitor 19 is proportional to the charge stored in the capacitor 19, it follows that the charging current is proportional to the negative gradient of the graph during the discharge regime 35, and the absolute value of this gradient decreases from an initial, relatively high value at time ti to a final, relatively low value at time t₂. By suitable selection of the second and third reference voltages V₂ and V₃, it is possible to determine the maximum and minimum values of the charging current supplied to the rechargeable battery 6. However, most rechargeable battery technologies require some form of temperature compensation: a typical level of temperature compensation for a 12V lead acid rechargeable battery having six cells is 18 mV per Celsius degree relative to 25 degrees Celsius, so that at 35 degrees Celsius the compensation would be -180 mV.

The values of V₁, V₂ and V₃ are therefore preferably additionally controlled in dependence on the ambient temperature, such that the values of these parameters are higher at low temperatures than at high temperatures, in which case a separate temperature sensor is preferably provided (not shown).

Although in the above arrangements, the two-way switch 16 is operated in dependence on the output voltage of the photovoltaic transducer 3, it would alternatively be possible to control the switch 16 in dependence on the output current of the photovoltaic transducer 3. Furthermore, although the charge levels in the capacitor 19 are determined by measuring the voltage across the capacitor 19, it would alternatively be possible to determine the level of charge in the capacitor 19 by measuring the current supplied both to and from the capacitor 19 and integrating this over time.

Claims

CLAIMS:

1. Apparatus for use with an electrically powered device which is operable in an ON mode, in which it consumes electrical power at a relatively high rate, and a STANDBY mode, in which it consumes electrical power at a relatively low rate, the apparatus comprising: a photovoltaic transducer arranged to be exposed to ambient light for generating an output electrical current in response thereto; a rechargeable battery arranged to receive as a charging current the output electrical current from the photovoltaic array; means for determining when the device is in the STANDBY mode; and means responsive to the determining means for supplying current from the rechargeable battery to the device only when it is determined that the device is in the STANDBY mode.

2. Apparatus as claimed in claim 1 , wherein the photovoltaic transducer comprises a dye-sensitised photovoltaic cell array.

3. Apparatus as claimed in claim 1 or claim 2, wherein the photovoltaic transducer is in the form of a flexible sheet.

4. Apparatus as claimed in any one of claims 1 to 3, further comprising means for accumulating charge from the photovoltaic transducer when the output electrical current is below a predetermined value and for supplying the charging current to the rechargeable battery at an instantaneous charging rate which is greater than the predetermined value.

5. Apparatus as claimed in claim 4, further comprising means for determining when the output electrical current is above the threshold value and, in response to a positive determination, for bypassing the charge accumulating means such that the rechargeable battery is supplied directly with the output electrical current from the photovoltaic transducer.

6. Apparatus as claimed in claim 4 or claim 5, wherein the charge accumulating means comprises a capacitor.

7. Apparatus as claimed in claim 5 or claim 6, further comprising a diode connected between the photovoltaic transducer and the charge accumulating means.

8. Apparatus as claimed in any one of claims 1 to 7, in combination with the electrically powered device.

9. Apparatus as claimed in claim 8, wherein the electrically powered device comprises a television receiver.

10. Apparatus as claimed in claim 8, wherein the electrically powered device comprises a radio receiver.

1 1. A method of supplying electrical power to a device which is operable in an ON mode, in which it consumes electrical power at a relatively high rate, and a

STANDBY mode, in which it consumes electrical power at a relatively low rate, the method comprising: supplying electrical power to the device from a photovoltaic transducer only during the STANDBY mode; and supplying electrical power to the device from a source other than the photovoltaic transducer during the ON mode.

12. A method as claimed in claim 1 1 , wherein the source other than the photovoltaic transducer comprises a mains electricity supply.

13. A method as claimed in claim 1 1 or claim 12, wherein the source other than the photovoltaic transducer comprises a battery.

14. A method as claimed in any one of claims 1 1 to 13, further comprising, when in the STANDBY mode, determining if there is sufficient electrical current available from the photovoltaic transducer to power the device, and in the event of a negative determination, supplying electrical power to the device from the source other than the photovoltaic transducer.

15. A method as claimed in any one of claims 1 1 to 14, further comprising storing the electrical charge generated by the photovoltaic transducer when the device is in the ON mode.

16. A method as claimed in any one of claims 11 to 15, wherein the photovoltaic transducer comprises a dye-sensitised photovoltaic cell array.