Patent ID: 8963431
Filing Date: 2015-02-24
Classification: H05B

Abstract:
1. A circuit, for driving a plurality of LED strings from an AC supply and arranged to, in use, drive current through a series arrangement of a plurality (N) of the LED strings when the AC voltage is sufficient to drive the plurality (N) of the LED strings: the circuit comprising a first current source configured to be switchably connected to said series arrangement of N LED strings; a series combination of a second current source and a heat dissipater, wherein the series combination of the second current source and the heat dissipater is arranged in parallel with the first current source; and a current balancer for balancing the current through the first current source and the second current source; wherein the first current source comprises a first transistor and the second current source comprises a second transistor, the first and second transistors having commonly connected emitters; the circuit further configured such that in use the sum of the currents I and the current balancer is operable to control the second transistor to control I