High efficiency LED driving method for odd number of LED strings

摘要

An arrangement wherein a plurality of LED strings are driven with a balanced drive signal, i.e. a drive signal wherein the positive side and negative side are of equal energy over time, is provided. In a preferred embodiment, the drive signal is balanced responsive to a capacitor provided between a switching network and a driving transformer. Balance of current between various LED strings is provided by a balancing transformer.

主权项

1. A driving arrangement for light emitting diode (LED) based luminaire comprising:
a driving transformer comprising a first winding and a second winding, the second winding magnetically coupled to the first winding; a switching control circuit; a switching bridge comprising a pair of electronically controlled switches coupled to a common node, each of the pair of electronically controlled switches responsive to an output of the switching control circuit; a direct current (DC) blocking capacitor coupled between the common node of said switching bridge and a first end of the primary winding of the driving transformer; a balancing transformer comprising a first winding and a second winding, the second winding magnetically coupled to the first winding; a first LED string; a second LED string; and a third LED string, a first end of said first LED string coupled to a first end of the second winding of said driving transformer, and arranged to receive electrical energy there from; a first end of said second LED string coupled to a second end of the second winding of said driving transformer, and arranged to receive electrical energy there from; a second end of said first LED string coupled to a first end of the first winding of said balancing transformer; a second end of said second LED string coupled to a second end of the first winding of said balancing transformer; and a first end of said third LED string coupled to the second winding of said balancing transformer, said switching control circuit arranged to provide a switching cycle comprising a first period wherein electrical energy is output from the second winding of said driving transformer with a first polarity, and a second period wherein electrical energy is output from the second winding of said driving transformer with a second polarity, the second polarity opposite the first polarity, said DC blocking capacitor arranged such that the total electrical energy output from the second winding of said driving transformer during the first period of the switching cycle is equal to the total electrical energy output from the second winding of said driving transformer during the second period of the switching cycle, and said balancing transformer arranged such that the average currents through said first LED string, said second LED string and said third LED string are equal.