LED DRIVER WITH COLOUR TEMPERATURE ADJUSTMENT [0001] This application is a divisional of Australian patent no. 2014210630, the entire content of which is incorporated herein by reference. Field [0001 a] The present invention relates to a LED (light emitting diode) driver with colour temperature adjustment. Background [0002] LED downlights are increasingly being used to replace incandescent and halogen downlights in residential and business settings. [0003] LED downlights have various disadvantages in retrofit residential and business installations. Some of these disadvantages are that they cannot be dimmed, and that they generally cannot change their output colour once they are installed to light power switches. Consequently, the output colour temperature of retrofitted LED downlights cannot be varied to provide mood lighting. [0004] In this context, there is a need for a LED driver with colour temperature adjustment that can be used with conventional dimmers and switches. Summary [0005] According to the present invention, there is a provided LED driver, comprising of: a power converter connectable between a light switch and a LED; a power detector connected to the power converter to detect when input power supply from the light switch is turned on and off; a controller connected to the power converter and the power detector, wherein the controller is operable to control the power converter to vary power supply output and hence change colour temperature of the LED depending on detecting an on/off time of the input power supply from the light switch. [0006] The controller may be operable in an automatic mode to change the colour temperature of the LED between a plurality of predetermined colour temperatures depending on a corresponding plurality of predetermined on/off times. [0007] The controller may be further operable in a manual mode to change the colour temperature of the LED between the plurality of predetermined colour temperatures depending on actuation of a selector switch connected to the controller. [0008] The plurality of predetermined colour temperatures may be three predetermined colour temperatures. [0009] The three predetermined colour temperatures may comprise a warm white colour temperature of about 3000-35000 K, a neutral white colour temperature of about 4000-45000 K, and a white colour temperature of about 6000-65000 K. [0010] The power converter may comprise a MOSFET switch connected to a valley fill rectifier that is connected to an output transformer and a rectifier. [0011] The light switch may comprise a triac dimmer. [0012] The power detector may comprise an input voltage detection circuit and an output current detection circuit. [0013] The controller may comprise a microcontroller having a pulse width modulation (PWM) generator to generate a PWM control signal for the MOSFET switch. [0014] The present invention further provides a LED lighting system comprising the LED driver described above and at least one LED light fitting. The at least one LED light fitting may comprise one or more of a LED oyster light, a LED troffer panel and a LED downlight. The LED driver may be separately or integrally provided with the at least one LED light fitting. [0015] The present invention also provides a method, comprising: converting input power supply from a light switch to output power supply to a LED; detecting when input power supply from the light switch is turned on and off; controlling output power supply to, and hence changing colour temperature of, the LED depending on detecting an on/off time of the input power supply from the light switch. Brief Description of Drawings [0016] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a functional block diagram of an example LED driver according to an embodiment of the invention; and Figure 2 is an example circuit diagram of the LED driver. Detailed Description [0017] Figure 1 is a functional block diagram of an example LED driver 10 according to an embodiment of the invention. The LED driver 10 may comprise a power converter 12 connectable between a light switch 14 and a LED 16. A power detector 18 may be connected to the power converter 12 to detect when input power supply from the light switch 14 is turned on and off. A controller 20 may be connected to the power converter 12 and the power detector 18. The controller 20 may be configured to be operable to control the power converter 12 to vary output power supply to, and hence change colour temperature of, the LED 16 depending on detecting an on/off time of the input power supply from the light switch 14. The LED driver 10 may further comprise electromagnetic compatibility (EMC) filter 22 connected between the light switch 14 and the power converter 12.
[0018] The controller 20 may be configured to be operable in an automatic mode to change the colour temperature of the LED 16 between a plurality of predetermined colour temperatures depending on a corresponding plurality of predetermined on/off times. The plurality of predetermined colour temperatures may be three predetermined colour temperatures. For example, the three predetermined colour temperatures may comprise a warm white colour temperature of about 3000-35000 K, a neutral white colour temperature of about 4000-45000 K, and a white colour temperature of about 6000-65000 K. Further or alternative colour temperatures may also be used. The automatic mode may be used by a user of the light switch 14 to automatically change the output colour temperature of the LED 16 among the three output colour temperatures by flicking the light switch 14 on and off. For example, the predetermined on/off times may be 0-3 seconds so that the LED changes between the three colour temperatures when the light switch is switched from on to off-on within 0-3 seconds. [0019] The controller 20 may be configured to be further operable in a reset mode to automatically restore the colour temperature to one of the three colour temperatures upon detecting transient or intermittent variation in input power supply due to factors such as interference. For example, the controller 20 may be operable to reset the colour temperature to white upon detecting input power supply for 3-15 seconds that is interrupted but restored within 2 seconds of the interruption. [0020] The controller 20 may be further configured to be further operable in a manual mode to change the colour temperature of the LED 16 between the plurality of predetermined colour temperatures depending on actuation of a push button selector switch (not shown) connected to the controller 20. The controller may be configured so that automatic mode is locked off when manual mode is actuated by the push button selector switch. The manual mode may be used by an installer of the LED driver 10 to manually set or change the output colour temperature of the LED 16. [0021] The light switch 14 may comprise a triac dimmer that provides leading, trailing edge or a variation of the two styles of dimming. The LED 16 may comprise a LED two-colour LED chip downlight having two output colour temperatures, for example, white and warm white. The controller 20 may be operable to control the power converter 12 to change the colour of the two-colour LED chip 16 between white and warm white, and to mix these two colours to output neutral white light. This may enable the LED driver 10 to variably power the two-colour LED chip 16 to selectively provide three output colour temperatures. [0022] Figure 2 is an example circuit diagram of the LED driver 10 and its functional components. The power converter 12 may comprise a MOSFET switch connected to a valley fill rectifier that is connected to an output transformer and a rectifier. The power detector 18 may comprise an input voltage detection circuit and an output current detection circuit. The controller 20 may comprise a microcontroller having a PWM generator to generate a PWM control signal for the MOSFET switch. The components of the LED driver 10 described above may be provided together on a printed circuit board (not shown). Other equivalent electrical circuits and components may also be used. [0023] The LED driver 10 described above may be separately or integrally provided with the LED 16 in at least one LED light fitting (not shown) to provide a LED lighting system with no special wiring requirements. The at least one LED light fitting may comprise one or more of a LED oyster light, a LED troffer panel and a LED downlight. For example, the LED driver 10 may integrally provided with the LED oyster light. Further or alternative LED light fittings may also be used. Multiple units may be wired to one control mechanism such as a switch, relay, automation system or push button for synchronised operation. For example, the push button selector switch described above may be removed to wire multiple units back to the one control mechanism. If one of the units goes out of synchronisation with other units, the LED driver 10 may be configured to be factory reset from the switch by, for example, switching the unit on and switching the unit off-on quickly after 5-10 seconds. [0024] Embodiments of the present invention provide a LED driver with colour temperature adjustment that can be used with conventional triac dimmers and light switches. Embodiments of the invention enable power to be adjusted from 10-100 W thereby allowing many different models of the LED driver to be manufactured for different residential and business installations.
[0025] For the purpose of this specification the word "comprising" means "including but not limited to", and the word "comprises" has a corresponding meaning. [0026] The above embodiments have been described by way of example only and modifications are possible within the scope of the claims that follow.