Ballast circuit

Abstract

A ballast circuit suitable for driving an LED or similar load, comprises a primary switch mode converter, means for measuring a modulation, such as a phase cut, as used for dimming light levels, on an input AC supply, a current regulator positioned in series with the load, and a feedback controller for controlling operation of the switch mode controller based upon measured modulation levels. The feedback controller is adapted to interrupt normal switching of the switch mode converter if modulation levels detected lead to the ballast working at a lower than desired efficiency (deep dimming), or if voltage levels across the current regulator are higher than desired. The feedback controller may have a further feedback means for controlling switch mode parameters during lower levels of modulation (shallow dimming). The circuit allows large dimming levels to be achieved without generating appreciable light flicker in the load.

Description

technical field

[0001] The present invention relates to ballasts and power circuits of the type commonly used to drive variable loads, such as dimmable light emitting diode (LED) lighting arrangements. More particularly, the present invention relates to ballasts and drivers particularly suitable for supplying loads such as LEDs, including organic LEDs (OLEDs), having means for reducing optical flicker that may occur during dimming processes. Background technique

[0002] LED lighting is beginning to become the mainstream choice for low-energy lighting. In order for LED technology to fully establish its credentials in the field and meet the current expectations of users, it is for LED-based lighting systems to provide control over the intensity of emitted light in response to "commands" or signals provided by dimming devices. A dimming device is very advantageous. Depending on the age, purpose and architecture of the lighting system, this device can take one of several form...

Images