DRIVING LIGHT EMITTING DIODES

摘要

The present invention relates to a driver for a string (STi) of series arranged light emitting diodes (D1i, D2i, D3i) of which at least two emit light having different spectra. The driver comprises a main power supply (PAi) which has outputs coupled across the string (STi) to supply a main current (IAi) to the string (STi). A secondary power supply (PBi) is coupled to at least one of junctions (J1i) between successive light emitting diodes (D1i, D2i) in the string (STi) to supply or withdraw a delta current (IBi) from the junction (J1i). The delta current (IBi) is at least a factor 5 smaller than the main current (IAi). A controller (CO) controls the secondary power supply (PBi) to generate the delta current (IBi) to obtain a desired spectral composition of the mixed light emitted by the string (STi).