FIELD OF THE INVENTION

This invention is generally related to a method and apparatus for controlling a load, for example a lighting apparatus, such as a lamp, luminaire, tubular luminaire, LED module or LED driver.

BACKGROUND OF THE INVENTION

There is an increasing use of LEDs as individual lamps or in luminaires, and which can perform additional functions beyond simple on-off control.

On-off control is typically achieved with a simple switch in series with the lighting load. The switch is in series with the mains power live line before it connects to the lighting load.

The most basic additional functionality to simple on-off control is to provide dimming control. Traditional incandescent light bulbs make use of phase-cut dimming approaches, and phase cut dimmer switches are used for this purpose. They may operate according to a leading edge phase cut approach or a trailing edge phase cut approach.

Lamps and luminaires with wireless radio frequency (RF) control functions, using an on-board radio modem, are becoming more popular, so that there is a trend towards wireless controllable lamps.

The wireless communication usually takes place between the lighting load (e.g. lamp) and a bridge, often known as a hub. The hub is preferably provided as a two-wire device to fit existing electrical installations so that it can be provided as a retrofit solution. The hub is then connected in series with the load, and it has to be powered in order to operate.

The lighting load has to be permanently powered by the mains to enable its internal RF receiver to remain powered to receive messages sent by the transmitter located at the switch. The mains switch is thus always closed.

The lighting load for example is controllable via ZLL, WiFi or Bluetooth wireless communication. Powering of the wall unit, which communicates wirelessly with the lighting load, can be implemented with batteries or other energy storage or energy harvesting technologies. Batteries have a limited lifetime and energy leakage during periods of non-use.

An energy harvesting approach derives a small amount of energy directly from the mains voltage. However, there is no neutral line close to the switch, and installing an extra neutral line to the switch is not an option as this requires infrastructure changes. The energy harvesting is achieved by creating a voltage drop along the series line. However, the energy harvesting approach introduces losses, which are undesirable.

WO 2015/015356 discloses various energy-harvesting and/or self-powered lighting systems. In various embodiments, a generator may be configured to capture kinetic energy from water moving through plumbing of a water provision appliance for storage as electrical energy in a rechargeable battery. A sensor may be powered at least in part by electrical energy stored in the rechargeable battery, and may be configured to provide a presence signal in response to detection of a person's presence near the water provision appliance. A power conversion circuit may be configured to use electrical energy stored in the rechargeable battery to selectively illuminate one or more LEDs near the water provision appliance based on the presence signal.

US 2016/0066396 discloses a wireless switch including a first energy harvester including a circuit, and a second energy harvester configured to open or close the circuit of the first energy harvester unit by an external operation. Hence, by using this approach, the wireless switch is able to operate without a requirement for providing a separate power supply.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to examples in accordance with an aspect of the invention, there is provided a control switch for controlling a load, comprising:

a power input terminal for receiving power from an external power source; an output terminal for connection to the load;

an energy harvesting circuit for generating a first output voltage, wherein the energy harvesting circuit has a series element arranged to provide a voltage drop induced by a current flowing to the output terminal, the first output voltage being based on the voltage drop; a DC-DC converter for receiving the first output voltage and for generating a second output voltage from the first output voltage, wherein the second output voltage is higher than the first output voltage; and

a circuit comprising a wireless transmitter arranged to be powered by the second output voltage for providing a wireless control signal to the load.

This switch combines a low voltage energy harvesting circuit with a DC-DC converter, in order to improve the efficiency and reduce losses. The series voltage drop is kept to a minimum so that the voltage is only sufficient to power up a low voltage startup DC-DC converter. The switch is for connection in series with a supply line, and provides a permanent connection between the power input terminal and the output terminal.

The circuit for example comprises a wireless transmitter for controlling the load. Thus, a basic switch function is replaced with a wireless control function for controlling a load. This gives additional control options. However, the energy needed for the wireless transmitter is obtained by energy harvesting so that a battery is not needed.

The switch may comprise a lighting apparatus control switch, wherein the load is a lighting load, and wherein the circuit comprises a wireless transmitter powered by the second output voltage for providing wireless control signals to the lighting load.

The DC-DC converter for example comprises a switch mode converter such as a boost converter. The DC-DC converter for example is for delivering a fixed output voltage.

The energy harvesting circuit preferably comprises an output capacitor, wherein a first side of the output capacitor is connected to the input terminal through a first diode, and a second side of the output capacitor is connected to the input terminal through a second, oppositely oriented, diode. These diodes function as a rectifier circuit to generate the required DC voltage for the DC-DC converter.

In one example, the energy harvesting circuit further comprises a series diode chain in parallel with the second diode, with the diodes of the series diode chain with opposite orientation to the second diode. The series diode chain is the element across which a voltage drop is induced which is then to be used to store a voltage on the output capacitor. The voltage stored is derived from (but not necessarily equal to) the voltage drop.

In another example, the energy harvesting circuit further comprises a series diode pair with a central node, in parallel with the output capacitor, a first series diode chain between the central node and the power input terminal, and a second series diode chain between the central node and the power input terminal, with the diodes of the first series diode chain with opposite orientation to diodes of the second series diode chain. This provides a double rectified diode configuration.

In another example, the energy harvesting circuit further comprises a transistor with its control terminal connected to the power input terminal through a first series diode chain. The diode chain provides a reference voltage to the transistor, and the transistor sets the harvested voltage. This arrangement provides a harvested voltage which is less dependent on the current drawn by the lighting load.

The energy harvesting circuit may further comprise a second transistor with its control terminal connected to the output terminal through a second series diode chain, with the diodes of the first and second series diode chains having opposite polarity. This provides a double rectified version.

The energy harvesting circuit may for example generate a first output voltage of less than 1.0V, for example less than 0.5V. The generated voltage may vary in dependence on the output load but remaining with a range such as 0.25V to IV, or 0.25V to 0.75V, or 0,25V to 0.5V. The DC-DC converter is for example implemented as an integrated circuit.

The invention also provides a lighting system, comprising a control switch as defined above and a lighting load connected to the output terminal.

Examples in accordance with another aspect of the invention provide a control method, comprising:

receiving power from an external power source and providing power to a load; using an energy harvesting circuit to generate a first output voltage by providing a voltage drop induced by a current flowing to an output terminal (16), the first output voltage being based on the voltage drop;

performing DC-DC conversion for generating a second output voltage of more than the first output voltage from the first output voltage; and

powering a circuit using the second output voltage.

The method may be for controlling a lighting load, wherein powering a circuit comprises powering a wireless transmitter using the second output voltage thereby to provide wireless control signals to the lighting load.

The DC-DC conversion for example comprises switch mode boost conversion and the energy harvesting includes rectifying. The energy harvesting for example comprises generating a voltage across a diode chain or across a transistor. BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

Fig. 1 shows a lighting system in schematic form including a lighting apparatus control switch for providing power to a lighting load;

Fig 2 shows a first example of energy harvesting circuit;

Fig 3 shows a second example of energy harvesting circuit;

Fig 4 shows a third example of energy harvesting circuit; and Fig 5 shows a lighting apparatus control switch in more detail.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention provides a control switch which uses an energy harvesting circuit to generate a first output voltage and a DC -DC converter is used for generating a second, greater, output voltage from the first output voltage. A circuit such as a wireless transmitter is powered by the second output voltage for example for providing wireless control signals to the load.

The invention will first be described with reference to the preferred application of the invention, as a control switch to be provided at a light switch, to implement wireless control the light which was previously controlled by a basic wired light switch. However, the invention may be applied to a switch for powering other types of electric device, by replacing wired on-off control with wireless control functionality. Furthermore, the circuit powered by the second output voltage may be for controlling devices other than the load which is powered through the switch. Thus, the invention is not limited to the control of the load which is supplied with power through the switch. It may be used to control other devices as well or instead of the load which receives power through the switch.

Figure 1 shows a lighting circuit. The circuit is powered by the mains, as represented by the voltage source 10. A single wire of the mains supply passes to a control switch 1 1 which includes an energy harvesting circuit 12 having a series element 13 across which a voltage drop is induced by the current flowing to a load. The single wire is a mains live line. The control switch 11 thus has a power input terminal 14 for receiving power from an external power source and an output terminal 16 for connection to the load in the form of a lighting device 18.

The circuit 12 provides a permanent connection through to the lighting device 18. The lighting device 18 includes a wireless receiver or transceiver 20 which is adapted to receive wireless control commands for the operation of the lighting device 18. In addition, the lighting device may perform other functions such as temperature sensing, PIR sensing, humidity detection or video surveillance. The outputs from these devices may be provided wirelessly from the lighting device, and input control commands may be received wirelessly.

The energy harvesting circuit 12 generates a low output voltage, below IV, for example in the range 0.25V to 0.5V. This low series voltage drop results in a low power loss.

A rectifier 22 is part of the energy harvesting circuit. The output voltage is provided to a DC-DC converter 24 for generating a second output voltage Vcc of more than IV from the first output voltage.

A wireless transmitter 26 is powered by the second output voltage Vcc for providing wireless control signals to the lighting device 18.

There are various possible designs for the energy harvesting circuit. A most basic approach is to generate a voltage across a series resistor, but this gives high losses. It is thus preferred to use diodes or transistors as explained below.

A first example is shown in Figure 2.

The circuit comprises the mains input 10 for providing power to a load 18. The mains input has an output which defines the power input terminal 14 for the energy harvesting circuit. A low voltage DC output 30 is provided across an output capacitor CI . A first side of the output capacitor CI is connected to the power input terminal 14 through a first diode Dl, and a second side of the output capacitor is connected to the power input terminal through a second, oppositely oriented, diode D2. These two diodes effectively function as a half bridge rectifier. The second side of the capacitor defines the output terminal 16 which connects to the load.

A series diode chain D3 is in parallel with the second diode D2, with the diodes of the series diode chain with opposite orientation to the second diode. In the example shown, the series diode chain D3 is arranged in the forward direction between the power input terminal 14 (i.e. the mains supply) and the load.

The series diode chain D3 defines a forward voltage drop during a positive half cycle of the mains. This forward voltage drop is stored on the capacitor CI, but after a voltage drop across diode Dl .

By suitable selection of components, a resulting voltage across capacitor CI can take a desired value for example in the range 0.25 to 0.5V. The resulting voltage is thus dependent on the forward voltage drops of the diodes of the series diode chain D3 and the diode Dl . Different diode technologies may be chosen to arrive at a desired resulting voltage. For example, the silicon diodes or Schottky diodes may be used, and diodes may be selected with the desired current- voltage characteristics to achieve the desired stored capacitor voltage. The diodes should be able to withstand the rated current of the load.

During a negative half cycle of the mains, the diode D2 conducts and the diode Dl is biased off so that the DC output is isolated, and the DC output voltage is retained by the capacitor. In this way, the diodes Dl and D2 form a half bridge rectifier, only charging the capacitor during one half cycle. The capacitor voltage is a floating voltage with its own floating ground potential at the anode of diode D2.

The DC output is maintained over a range of output loads, for example 0.2W up to 100W or even higher, for example up to 600W.

Figure 3 shows a modification to Figure 2 to provide full rectification so that the output capacitor is charged during both half cycles of the mains. The same components are given the same references as in Figure 2.

A series diode pair D4, D5 is provided with a central node, in parallel with the output capacitor. The diodes D4, D5 of the series diode pair are in the forward direction from the low voltage terminal to the high voltage terminal of the output 30. Thus, they are biased in the reverse direction by the output 30.

The series diode chain D3 is now between the central node and the power input terminal, and there is a second series diode chain D6 also between the central node and the power input terminal, with the diodes of the series diode chain D3 with opposite orientation to diodes of the second series diode chain D6. The node forms the output terminal 16 of the circuit.

During the positive half cycle, the circuit functions in the same way as the circuit of Figure 2, but with the additional diode D5 in the capacitor charging circuit. In the negative half cycle, the charging path is from the output terminal, through diode D4 to the capacitor CI, and then back to the power input terminal 14 through the diode D2.

One series chain defines a controlled voltage drop in the positive half cycle and the other defines a controlled voltage drop in the negative half cycle. The diodes Dl, D2, D4, D5 now function as a full bridge rectifier.

A problem with these circuits is that, particularly at small output loads, there are still significant losses in the diodes. A light load gives rise to increased currents and voltage drops across the diode chains, and consequently greater power loss. If multiple diodes are used in order to achieve the desired DC voltage, there are again additional power losses. The diode current-voltage curve has some regions of linear behavior which give rise to power losses.

The voltage drop and therefore circuit output is also dependent on the output load and therefore current flowing.

Figure 4 shows a more efficient circuit design. Instead of having a voltage generated which depends on the current flowing through a diode or series of diodes, diodes are used to generate a reference voltage source for a transistor. A transistor may be operated with a bias created by a diode or a MOSFET with a gate/source threshold. A diode used to bias a transistor may operate in a very low current mode due to the transistor amplification and therefor the voltage is constant. The transistor may then runs linearly up to a point given by such a bias diode. In this way, power losses over a wide range of load powers (0W to 600W) may be kept as low as possible.

The circuit comprises a transistor Tl with its control terminal (base in the case of a BJT) connected to the power input terminal 14 through a series diode chain D7. The base current provided to the transistor is less dependent on the output load giving a more stable generated DC voltage.

Figure 4 shows a half bridge rectifier arrangement.

Figure 5 show a full implementation of the lighting control switch based on the arrangement of Figure 4 but with full rectification.

The circuit has a first transistor Tl with its based coupled to the power input terminal 14 through the forward diode chain D7 as in Figure 4. A second transistor T2 is provided with its control terminal (base) connected to the output terminal 16 through a second series diode chain D8, with the diodes of the first and second series diode chains having opposite polarity. The second series diode chain has diode in their forward direction from the output terminal to the base. The diodes Dl, D2, D4, D5 provide full rectification as in the examples above.

During the positive half cycle, a voltage drop is defined across the transistor Tl (and an additional diode D9). This voltage is also present across the capacitor CI and rectifier diodes Dl and D5, which thereby define the capacitor voltage. The other diodes are all off.

During the negative half cycle, a voltage drop is defined across the transistor T2 (and an additional diode D10). This voltage is also present across the capacitor CI and rectifier diodes D4 and D2, which thereby define the capacitor voltage which has the same polarity as in the positive half cycle. The other diodes are all off. The diodes Dl, D2, D4 and D5 thus form a full bridge rectifier as in the examples above.

The capacitor voltage is output to a DC-DC boost converter 50. The negative terminal of the capacitor C 1 defines a floating ground potential which is also the ground potential for the capacitor C2, and the positive terminal of the capacitor C 1 defines the DC high output voltage provided to the DC-DC converter 50. The converter 50 is an integrated circuit boost converter, with an external inductor LI . The boost converter output is provided on an output capacitor C2.

The boost converter is a low voltage start up converter, for example requiring a low input voltage for example with a minimum level of between 0.25 V and 0.5 V. The output of the boost converter is any required voltage level required by the wireless transmitter or transceiver circuit, such as 3.3V or 5V. The boost converter has a wide input range.

The energy harvesting circuit may be any of the types described above, and other circuits are also known.

The lighting control switch may be applied to LED lamp or luminaires, CFL lamps or luminaires, incandescent lamps or luminaires and wireless controllable lamps or luminaires in a two-wire electrical installation. The lighting apparatus control switch

(combining the energy harvesting and the RF transmitter) may be fitted into a wall socket.

As mentioned above, the lighting device may not be limited to lighting only. Various other functions such as acoustic functions, sensing functions, and image capture can be integrated into a lamp or luminaire. The lamp and luminaires can also house functionality which can be part of a larger system, e.g. heating, ventilation and air conditioning (HVAC) systems, load-shedding systems, and emergency and alarm security systems.

Furthermore, the circuit powered by the harvested DC voltage is not limited to a wireless control circuit. For example, the circuit may be an infrared controller, or it may be light sources to illuminate the switch.

The invention may be applied to device other than lighting units. Indeed, and series single- wire switch may be replaced with the control switch to convert from basic wired on-off control to wireless control, or simply to generate power for a circuit to be located at the switch location, such as local lighting.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Where elements have been defined separately by their function, such as a detection circuit and a controller, this does not exclude that they may be implemented in practice as a shared physical entity. Any reference signs in the claims should not be construed as limiting the scope.