WO2016107761A1

WO2016107761A1 - Led driver

Info

Publication number: WO2016107761A1
Application number: PCT/EP2015/080546
Authority: WO
Inventors: Glenn VAN DER WOLK; Marcel Beij
Original assignee: Philips Lighting Holding B.V.
Priority date: 2015-01-02
Filing date: 2015-12-18
Publication date: 2016-07-07

Abstract

The invention describes an LED driver (1) realized to drive an LED light source (2) from a rectified mains voltage (3), comprising an energy-metering circuit realized to monitor power consumption of the LED light source (2), which energy-metering circuit comprises a current measurement circuit (10) comprising a voltage shift circuit portion (10R) realized to shift a negative current-sense signal (S_{i_neg}) above a zero volt level such that the current measurement circuit (10) provides a positive current-sense signal (S_{i_ pos}) to an analogue-to-digital converter (16) of the LED driver (1). The invention further describes a method of monitoring the power consumption of an LED light source (2) of an LED lighting arrangement (100); and an LED lighting arrangement (1).

Description

LED driver

FIELD OF THE INVENTION

The invention describes an LED driver, a method of monitoring the power consumption of an LED light source; and an LED lighting arrangement. BACKGROUND OF THE INVENTION

In some lighting applications that use light-emitting diodes as a light source and are realised for connection to a rectified mains voltage, it can be necessary to monitor the power consumption of the LEDs for various reasons. For example, verification of power consumption of a lighting system may be required for remuneration of energy costs. To this end, such an LED lighting arrangement can include an analogue-to-digital converter (ADC) as part of an energy-metering circuit, placed between the input terminals (that connect to a rectified mains input) and a driver stage. Measured values of voltage and current - representing the voltage and current of the LED light source - are provided to the ADC, which samples the inputs and computes the consumed power. A microcontroller of the LED lighting arrangement can then use this information to control operation of the driver.

To ensure that the energy metering does not have any adverse effect on the functionality of the driver stage, and to ensure that electromagnetic interference does not arise as a result of the energy metering, any current sense resistor that is used to measure the current must be placed between the circuit ground and the rectifier. As a result, the current- sense signal will be negative, i.e. it will have a voltage that is always below zero. However, an ADC used to sample the measured voltage and current values can generally only handle positive signal inputs, so that conventional energy-metering circuits require an inverter stage to change the negative current-sense signal into a positive current-sense signal. This adds to the overall complexity, cost and size of the driver of such an LED lighting arrangement.

Therefore, it is an object of the invention to provide an alternative way of performing energy-metering that avoids the problems mentioned above. SUMMARY OF THE INVENTION

The object of the invention is achieved by the LED driver of claim 1 ; by the method of claim 10 of monitoring the power consumption of an LED light source; and by the LED lighting arrangement of claim 12.

According to the invention, the LED driver realized to drive an LED lighting arrangement from a rectified mains voltage, comprising an energy-metering circuit realized to monitor power consumption of the LED lighting arrangement, which energy-metering circuit comprises a current measurement circuit comprising a voltage shift circuit portion realized to shift a negative current-sense signal above a zero volt level such that the current measurement circuit provides a positive current-sense signal to an analogue-to-digital converter of the LED driver.

An advantage of the LED driver according to the invention is that the circuitry used to obtain the positive current sense signal is relatively straightforward, so that the energy-metering function can be realized in a low-cost manner. Less circuit components are required compared to conventional energy-metering realizations. Even so, the accuracy of the energy-metering in the current measurement circuit of the LED driver according to the invention is comparable to the prior art solutions.

According to the invention, the method of monitoring the power consumption of an LED light source comprises the steps of arranging an analogue-to-digital converter between a mains voltage rectifier and a driver stage of an LED lighting arrangement comprising the LED light source; sensing the voltage across input terminals of the driver stage and providing a voltage-sense signal to the analogue-to-digital converter; and sensing an LED current and providing a positive current-sense signal to the analogue-to-digital converter; and determining the power consumption of the LED light source on the basis of the voltage-sense signal and the positive current-sense signal.

An advantage of the method according to the invention is that the step of providing a positive current-sense signal to the analogue-to-digital converter obviates the need to invert a negative current-sense signal, so that the circuitry can be realized in a more economical manner.

According to the invention, the LED lighting arrangement comprises an LED light source comprising a number of light-emitting diodes; input terminals for connecting to an AC power supply; and a driver according to the invention for driving the LED lighting arrangement and for providing power consumption information of the LED light source to an external device. An advantage of the LED lighting arrangement according to the invention is that it can be realised in a cost-effective manner - i.e. with relatively little additional effort - to provide energy-metering information. An LED lighting arrangement according to the invention can therefore be more attractive to consumers who require power consumption statistics for the energy-efficient light sources that they use.

The dependent claims and the following description disclose particularly advantageous embodiments and features of the invention. Features of the embodiments may be combined as appropriate. Features described in the context of one claim category can apply equally to another claim category.

The invention is directed at a simpler way of determining how much power is consumed by an LED light source. To determine power consumption by an electrical load, it is generally necessary to determine the current through the load, as well as the voltage across the load. Generally, these parameters may not be exactly measurable owing to the nature of current and voltage measurement, and owing to the presence of other circuit components of an LED lighting arrangement that consume a fraction of the overall power. In the context of the invention, therefore, the expression "to measure power consumption of an LED light source" may be understood to mean that the measurement indicates the power consumed by the driver and LED load, but need not necessarily be an exact measurement of that power. For example, the measured value of power consumption may indicate the power consumed by the complete LED luminaire, comprising driver and LED load, to which an estimated value of the rectifier losses is later added.

As indicated above, prior art energy-metering circuits make use of a current sense resistor placed between the circuit ground and the rectifier. This is the simplest way to sense the current drawn by the LED light sources without having any negative impact on the functionality of the driver stage, and without causing any electromagnetic interference. These issues are also relevant for the LED driver according to the invention. Therefore, in a particularly preferred embodiment of the invention, the current measurement circuit comprises a current sense resistor for providing the negative current-sense signal, and wherein the current sense resistor is connected between circuit ground and a rectifier. In other words, a first stage in obtaining a positive current sense signal simply uses the same approach as the known circuits. The current sense resistor effectively provides a scaled-down version of the current through the LED light source.

Instead of using a complex inverter stage to invert such a negative current- sense signal, the current measurement circuit according to the invention takes the approach of raising the negative current-sense signal above the zero volt level. This can be achieved in any suitable manner. For example, an arrangement comprising a voltage divider and Zener diode may be used for this purpose. However, in a particularly preferred embodiment of the invention, the voltage shift circuit portion comprises a shunt regulator connected to shift the negative current-sense signal above the zero volt level. A shunt regulator acts to raise an input voltage by a certain amount, and the amount by which the output signal is shifted can be controlled by a reference input to the shunt regulator.

The maximum amplitude or 'swing' of the driver current measured by the current sense resistor (neglecting the losses in the rectifier) can vary between different types of LED arrangement, depending for example on the driver losses, on the LED load, and on the LED current settings. The shunt regulator can be chosen according to the maximum current swing for a particular LED arrangement, so that the current measurement circuit can effectively be tailored to the maximum current drawn by the LEDs. However, in a particularly preferred embodiment of the invention, the shunt regulator is realized as an adjustable or programmable shunt regulator. In this way, the same component- for example a relatively cheap off-the-shelf programmable shunt regulator - can be used for various different LED driver designs, and the operation of each regulator can be tailored as required by connecting a voltage reference pin of the programmable shunt regulator to an appropriate reference voltage. This allows for a particularly economical realization over several design series. Adjustments can also be made by varying the current sense resistor, i.e. by choosing an appropriate resistor value at the design stage.

The current measurement circuit is able to provide the analogue-to-digital converter (ADC) with a positive input signal that is representative of the current through the LEDs. To determine the power consumption of the LED light source, a measurement of the voltage across the LED light source is also required. Therefore, in a further preferred embodiment of the invention, the LED driver comprises a voltage measurement circuit realized to provide a voltage-sense signal to the analogue-to-digital converter. The voltage measurement circuit can be realized in essentially the same way as known from the conventional energy metering solutions. For example, in a preferred embodiment of the invention, the voltage measurement circuit comprises a voltage divider connected across input terminals of the driver. The output of the voltage divider is then a scaled-down version of the voltage across the LED light source. The current measurement circuit and the voltage measurement circuit preferably each comprise an anti-aliasing filter to adjust the bandwidth of the signal provided to the ADC. Generally, a first-order anti-aliasing filter is sufficient for the ADC to accurately sample the analogue input signal.

Preferably, the analogue-to-digital converter of the LED driver is realized to provide power consumption information based on the positive current-sense signal and the voltage-sense signal. As mentioned above, power consumption information can be required by users of an LED lighting arrangement for the purposes of remuneration, for example in cases where the use of energy-efficient lighting is subsidised or otherwise financially encouraged. Power consumption of the LED light source can be calculated by a

microcontroller of the LED driver, using the scaled-down values of current and voltage provided by the current measurement circuit and the voltage measurement circuit. This information can then be provided to an external device such as a smartphone, tablet computer, personal computer, etc. A proprietary interface and protocol could be used to transfer and interpret this information. Alternatively, a standard interface and protocol could be used. In a preferred embodiment of the invention, therefore, the LED driver comprises a digital addressable lighting interface (DALI) for transmitting power consumption data to an external device. Preferably, power and energy consumption information is provided at regular intervals or upon request to an external device or to a user.

Other objects and features of the present invention will become apparent from the following detailed descriptions considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig 1 shows a first embodiment of the LED lighting arrangement according to the invention;

Fig 2 shows a second embodiment of the LED lighting arrangement according to the invention;

Fig. 3 shows sensed waveforms of the energy-metering circuit of the LED lighting arrangement of Fig. 2;

Fig 4 shows a third embodiment of the LED lighting arrangement according to the invention;

Fig 5 shows a fourth embodiment of the LED lighting arrangement according to the invention;

Fig. 6 shows a prior art LED lighting arrangement; Fig. 7 shows sensed waveforms of an energy-metering circuit of a prior art LED lighting arrangement.

In the drawings, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig 1 shows a first embodiment of the LED lighting arrangement 1 according to the invention. The diagram shows an LED light source 2 that can comprise any number of light-emitting diodes 20. The LED light source 2 is driven by a driver stage 14, 15, which in this embodiment comprises a first stage 14 for performing power-factor correction (PFC), and a second stage 15 for providing the required current and voltage levels to the LED light source 2. The LED lighting arrangement 1 comprises a rectifier stage 13 for converting an AC mains voltage (for example from a household mains supply 3) to a rectified voltage VBUS- In this exemplary embodiment, an EMI filter and surge protection module 12 is arranged between the mains supply 3 and the rectifier stage 13.

The diagram shows an energy-metering circuit arranged between the rectifier stage 13 and the PFC stage 14. The energy-metering circuit is used to monitor power consumption of the LED light source 2 and comprises a positive-voltage-based ADC 16, in other words an ADC that requires its input signals to be positive. Such an ADC cannot handle negative input signals. Therefore, the energy-metering circuit of the driver 1 according to the invention comprises a current measurement circuit 10 that provides a current measurement signal S,_p₀s to the ADC 16 in the form of a positive voltage waveform Si__pos, i.e. the current measurement signal Si__pos that is input to the ADC 16 is never below 0 V. The energy-metering circuit of the driver 1 also comprises a voltage measurement circuit 1 1 that provides a voltage measurement signal S_v to the ADC 16. The ADC 16 converts the positive analogue voltages S,_p₀s, S_v into digital signals which can be interpreted, analysed or otherwise processed by a further component such as a microcontroller (not shown). To ensure correct sampling of the current and voltage measurement signals S,__Pos, S_v, an anti-aliasing filter R_f, C_f is used between each of the voltage measurement circuit 1 1 and current measurement circuit 10 and the ADC 16.

Fig. 2 shows a second embodiment of the LED lighting arrangement 1 according to the invention. Here, the current-sense signal is obtained by measuring the voltage drop across a sense resistor R_sense located between the rectifier 13 and circuit ground, and using a programmable shunt regulator 10R to shift this negative sensed voltage above the 0 V level. In this realisation, the programmable shunt regulator 10R can be an off-the-shelf component, and the reference voltage input in this case is connected to the device's cathode realizing a voltage equal to the device's internal reference value (in an alternative

embodiment, additional circuitry could be used to obtain a different desired reference voltage, as will be known to the skilled person).

In this embodiment, the voltage across the LED light source, corresponding to the bus voltage VBUS, is sensed by a voltage divider R_{1 ;} R₂ . The voltage measurement signal S_v supplied to the ADC 16 is positive and needs no adjustment.

The diagram shows a microcontroller 17 of the LED driver 1 , which is used to perform various functions such as controlling the power stages, for controlling a

communications interface such as a DALI interface, and for controlling a current setpoint . Such a microcontroller 17 may already incorporate an ADC 16, as shown here. The ADC 16 converts the input signals of sensed voltage S_v and sensed current Si__pos into digital signals that can be analysed in an analysis unit 1 8 of the microcontroller 17 to compute the power consumed by the LED light source 2. This information can be sent to an external device 5 over a DALI interface 19, which is shown in this exemplary embodiment to be incorporated in the microcontroller 17.

For the microcontroller 17 to be able to correctly determine the LED current ILED on the basis of the measured current signal S|_p₀s_;; it need only be informed of the magnitude of the voltage shift performed by the shunt reference 1 OR and the magnitude of the sense resistor R_sense- Similarly, the microcontroller 17 is informed of the resistor values of the voltage divider R_{1 ;} R₂ so that it can compute the actual bus voltage VBUS- With the determined values 160 of bus voltage VBUS and LED current I_LED , the analysis unit 1 8 can compute the power consumption. This can be done intermittently, at regular intervals, or continuously, depending on the manner in which the microcontroller 17 is programmed. The microcontroller 17 can provide the external device 5 with values 170 of power consumption information upon request or at regular intervals, etc., as appropriate.

Fig. 3 shows exemplary voltage waveforms Si__neg, Si__p0s for the sensed current Sr neg at the current sense resistor R_sense, and the sensed current S,__Pos at the input to the ADC 16. As the diagram shows, the sensed current S,__neg at the current sense resistor R_sense is negative, with a swing of - 1 .2 V. This signal cannot be used directly by the ADC 16 of Fig. 1 . After shifting upwards by the adjustable shunt regulator 10R, a positive voltage waveform S_{i p}os, which does not drop below a level of 0 V, is obtained. This positive current sense signal S,_p₀s can be used directly by the conventional ADC 16. Fig. 4 shows a third embodiment of the lighting arrangement 100 according to the invention. This embodiment is similar to the embodiments described above, but in this case the current measurement circuit comprises a programmable shunt reference 1 OF which is set to a certain fixed value by means of resistors RIOA, RIOB- This embodiment may be preferred when the ADC's reference voltage is higher than the voltage regulator's internal reference, in which case the regulator's voltage and the current sense resistor can be adapted to allow a larger swing. In this way, the ADC's full range can be completely utilized, thereby achieving a higher accuracy of measurement. In this embodiment, the maximum absolute value of the voltage at the current sense resistor R_sense should not exceed the programmed voltage level.

Fig. 5 shows a fourth embodiment of the lighting arrangement 100 according to the invention. Again, this embodiment shares constructional detail with the embodiments described above, but in this case the current measurement circuit simply comprises a Zener diode or a shunt reference 10Z in which the program pin is hardwired, i.e. internally connected, to the cathode of the diode.

Fig. 6 shows a prior art LED lighting arrangement 6 with an architecture that shares various details with that of the LED lighting arrangement according to the invention. In this prior art realization, an inverter circuit 60 is required in order to convert the negative current sense voltage S,__neg into a positive voltage signal 600. The inverter circuit 60 uses an operational amplifier to achieve the inversion. However, as explained in the introduction, this approach is associated with higher costs than the inventive solution, and additional circuitry may be needed to improve the accuracy due to non-ideal effects of the op-amp such as offset voltage, offset current, etc.

Fig. 7 shows sensed waveforms Si__neg , 600 of the energy-metering circuit of the prior art LED lighting arrangement 6 of Fig. 6. Here, the negative current sense signal

Si neg is shown in the upper part of the diagram, and the inverted positive current sense signal 600, obtained by the inverter circuit arrangement 60, is shown in the lower part of the figure.

Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

For the sake of clarity, it is to be understood that the use of "a" or "an" throughout this application does not exclude a plurality, and "comprising" does not exclude other steps or elements. The mention of a "unit" or a "module" does not preclude the use of more than one unit or module.

Claims

CLAIMS:

1. An LED driver (1) realized to drive an LED light source (2) from a rectified mains voltage (3), comprising an energy-metering circuit realized to monitor power consumption of the LED light source (2), which energy-metering circuit comprises

a current measurement circuit (10) comprising a voltage shift circuit portion (10R) realized to shift a negative current-sense signal (S,__neg) above a zero volt level such that the current measurement circuit (10) provides a positive current-sense signal (S,__p0s) to an analogue-to-digital converter (16) of the LED driver (1).

2. An LED driver according to claim I , wherein the current measurement circuit (10) comprises a current sense resistor (R_sense) for providing the negative current-sense signal

(Sr neg), and wherein the current sense resistor (R_sense) is connected between circuit ground and a rectifier (13).

3. An LED driver according to claim 1 or claim 2, wherein the voltage shift circuit portion (10R) comprises a shunt regulator (10R) connected to shift the negative current-sense signal (Si__neg) above the zero volt level.

4. An LED driver according to claim 3, wherein the shunt regulator (10R) is realized as an adjustable shunt regulator (10R).

5. An LED driver according to any of the preceding claims, comprising a voltage measurement circuit (1 1) realized to provide a voltage-sense signal (S_v) to the analogue-to- digital converter (16).

6. An LED driver according to claim 5, wherein the voltage measurement circuit

(1 1) comprises a voltage divider (R_1; R₂) connected across terminals of a rectifier (13) of the driver (1).

7. An LED driver according to any of the preceding claims, comprising an antialiasing filter (R_f, C_f) between a measurement circuit (10, 1 1) and the analogue-to-digital converter (16).

5 8. An LED driver according to any of the preceding claims, wherein the

analogue-to-digital converter (16) is realized to provide digital current and voltage data (160) to a microcontroller (17) of the LED lighting arrangement (1).

9. An LED driver according to any of the preceding claims, comprising a digital 10 addressable lighting interface (19) for transmitting power consumption data (170) to an

external device (5).

10. A method of monitoring the power consumption of an LED light source (2) of an LED lighting arrangement (100), which LED light source (2) comprises a number of

15 LEDs (20), which method comprises the steps of

arranging an analogue-to-digital converter (16) between a mains voltage rectifier (13) and a driver stage (14, 15) of the LED lighting arrangement (100);

sensing the voltage (VBUS) across terminals of the driver stage (14, 15) and providing a voltage-sense signal (S_v) to the analogue-to-digital converter (16); and

20 - sensing an LED current (ILED) and providing a positive current-sense signal

(Sr pos) to the analogue-to-digital converter (16); and

determining the power consumption of the LED lighting source (2) on the basis of the voltage-sense signal (S_v) and the positive current-sense signal (S_{i p}os)-

25 1 1. A method according to claim 10, comprising the step of providing power consumption information (170) to an external device (5).

12. An LED lighting arrangement (1) comprising

an LED light source (2) comprising a number of light-emitting diodes (20); 30 - input terminals for connecting to an AC power supply (3);

a driver (1) according to any of claims 1 to 9 for driving the LED lighting arrangement (1) and for providing power consumption information (170) of the LED light source (2) to an external device (5).

13. An LED lighting arrangement according to claim 12, comprising a microcontroller (17) for evaluating digital current and voltage data (160) supplied by the analogue-to-digital converter (16).