Patent ID: 7538497
Filing Date: 2009-05-26
Classification: G02F,G09G,H05B

Abstract:
1. A constant current driving unit for constant current driving a plurality of light emitting devices by a pulse width modulating constant current driving circuit, comprising: a bypass circuit including (a) a plurality of thyristors, each of which is connected in parallel with a respective one of said series connected light emitting diodes, and (b) a gate potential setting circuit; a switching device for pulse width modulation; and a resistor connected in parallel with said switching device for pulse width modulation, wherein, said gate potential setting circuit provides to said thyristors a gate potential value such that, when said light emitting devices are operating normally, said thyristors are in the off state, said gate potential setting circuit provides to said thyristors another gate potential value such that, when said light emitting devices are in the open state, said thyristors are on, and said resistor is coupled to said pulse width modulating constant current driving circuit via a transistor such that current for maintaining the on state of a turned-on thyristor flows through said resistor when said transistor is off.