Monitor device for a lighting arrangement, a driver using the monitoring arrangement, and a driving method
A monitor device is provided for monitoring a lighting arrangement of lighting elements of unknown electrical load, and a driver using the monitoring arrangement. A set of duty cycles is applied to switches which control sub-sets of lighting elements thereby to create a desired light output. With this desired duty cycle setting, the current for an individual duty cycle period is monitored, in particular to detect variations in a current plateau level 5 within the individual duty cycle period. This is used to determine a power consumption of the lighting arrangement and to adjust the duty cycles as a function of the detected current. This avoids the need to probe the sub-sets of lighting elements individually in order to determine the nature of the load and its power consumption.
1. A monitor device for monitoring a lighting arrangement of lighting elements, wherein the lighting arrangement is associated with a switch arrangement for coupling a DC voltage to the lighting arrangement, wherein the switch arrangement comprises a set of switches, each of which is for connection to a sub-set of the lighting elements, wherein the monitor device comprises:
a controller for providing control signals for controlling the switch arrangement using pulse width modulation, wherein the controller is adapted to:
apply a set of duty cycles to the set of switches at the same time thereby to create a user-selected light output;
monitor a current through the lighting arrangement at a plurality of times within an individual duty cycle period thereby to detect a plurality of current plateaus within the duty cycle period;
determine a power consumption of the lighting arrangement based on the detected current plateaus and the set of duty cycles; and
adjust the duty cycles according to the detected current plateaus; and
wherein the controller is adapted to apply a first set of duty cycles which is a scaled down version of a desired set of duty cycles and monitor the current for an individual duty cycle period; and progressively increase the scaling of the set of duty cycles.
2. The device as claimed in claim 1 , wherein the controller is adapted to determine the current flowing through each sub-set of lighting elements based on an analysis of the set of different current levels.
3. The device as claimed in claim 1 , wherein the controller is adapted to set a maximum duty cycle for each duty cycle of the set of duty cycles based on the determined power consumption of the load and a load rating of a driver.
4. The device as claimed in claim 1 , wherein the controller is adapted to:
monitor the current for a set of sequential individual duty cycle periods; and
determine an average current for each plateau over the set of sequential duty cycle periods; and
determine the power consumption from the average currents.
5. The device as claimed in claim 1 , wherein the controller is adapted to derive a moving average of the monitored currents for each plateau.
6. The device as claimed in claim 1 , wherein the controller is further adapted to monitor the DC voltage and to adjust the set of duty cycles in response to a change in the DC voltage thereby to maintain a constant light output flux from the lighting arrangement.
7. A driver for the lighting arrangement of lighting elements, comprising:
a DC voltage source;
the switch arrangement for coupling the DC voltage source to the lighting arrangement, wherein the switch arrangement comprises a set of switches, each of which is for connection to a sub-set of the lighting elements;
a current sensor for sensing a current to the overall lighting arrangement; and
a monitor device as claimed in claim 1 .
8. A lighting apparatus comprising:
the driver as claimed in claim 7 ; and
a lighting arrangement driven by the driver, wherein the lighting arrangement is user-configurable.
9. A lighting method for providing lighting using an arrangement of lighting elements, comprising:
coupling a DC voltage source to the lighting arrangement using a switch arrangement which comprises a set of switches, each of which is for connection to a sub-set of the lighting elements;
controlling the switch arrangement using pulse width modulation to apply a set of duty cycles to the set of switches at the same time thereby to create a user-selected light output;
monitoring a current provided to the overall lighting arrangement within an individual duty cycle period thereby to detect a plurality of current plateaus within the duty cycle period;
determining a power consumption of the lighting arrangement based on the detected current plateaus and the set of duty cycles;
adjusting the duty cycles according to the detected current plateaus;
applying a first set of duty cycles which is a scaled down version of a desired set of duty cycles and monitoring the current for an individual duty cycle period;
progressively increasing the scaling of the set of duty cycles; and
deriving a moving average of the monitored currents.
10. The method as claimed in claim 9 , comprising determining the current flowing through each sub-set of lighting elements based on an analysis of the set of different current levels.
11. The method as claimed in claim 9 , comprising setting a maximum duty cycle for each duty cycle of the set based on the determined power consumption of the load and a load rating of a driver.
12. The method as claimed in claim 9 comprising:
monitoring the current for a set of sequential individual duty cycle periods;
determining an average current for each plateau over the set of sequential duty cycle periods; and
determining the power consumption from the average currents.
13. A non-transitory computer program comprising computer program code which is adapted, when said computer program code is run on a computer, to implement the method of claim 9 .