Open-circuit protection circuit of constant current driving circuit for light emitting diodes

Abstract

A open-circuit protection circuit of a constant current driving circuit for light emitting diodes is disclosed, which includes that: a transformer (Ta), which has at least one secondary winding (WT), is connected to at least two load branches (A, A); a commutating loop is composed of each load branches (A, A) and one secondary winding (WT), wherein the secondary winding (WT) has tap ends; a current sharing transformer (T) is set in two neighbor load branch (A, A); each load branch (A, A) is separately connected to one open-circuit protection module (). The open circuit protection module () includes: a detection control unit (), used for outputting a control signal to a processing unit () when the detection control unit detects that the output voltages of each load branch (A, A) or the voltages proportionate to the output voltages are not less than a corresponding preset threshold; the processing unit (), used for shorting one secondary sub winding (WT, WT) in the corresponding load branch (A, A) and a sharing current winding (W) of the current sharing transformer (T) in series with the secondary sub winding (WT, WT) when receiving the control signal. With the embodiments of the present invention, the cost and the bulk of the current sharing transformer (T) can be reduced.