Backlight module and driving circuit

Abstract

A backlight module and a driving circuit are provided. The driving circuit includes a plurality of current sources and a current switching unit. The current sources provide a plurality of driving currents. The current switching unit is coupled between a plurality of light emitting element strings and the current sources for transmitting the driving currents to the light emitting element strings, and switching the driving currents received by the light emitting element strings by timing. Therefore, the brightness of the light emitting element strings can be equalized.

What is claimed is: 
     
       1. A driving circuit, adapted to drive a plurality of light emitting element strings, the driving circuit comprising:
 a plurality of current sources, for respectively providing a plurality of driving currents; and 
 a current switching unit, coupled between the light emitting element strings and the current sources, transmitting the driving currents provided by the current sources to each of the light emitting element strings in order for a plurality of periods equally divided in a time interval, wherein each of the driving currents is correspondingly and rotatably transmitted between the light emitting element strings over the plurality of periods, wherein the same light emitting element string receives different driving currents for two adjacent periods, and a light emitting brightness of each of the light emitting element strings are related to an average of the driving currents, 
 wherein the current switching unit comprises:
 a plurality of first switch groups, each of the first switch groups comprising:
 n first switches, having first ends respectively coupled the corresponding light emitting element string, wherein n is a positive integer; and 
 n second switches, having first ends respectively coupled to second ends of the first switches, and second ends respectively coupled to the corresponding current source, 
 wherein a second end of an i-th first switch of each of the first switch groups is coupled to a second end of an i-th first switch of the adjacent first switch group, i is a positive integer and 1≦i≦n, one of the first switches and one of the second switches are turned on, and the turned on first switch and the turned on second switch are switched by timing, and in different first switch groups, the turned on first switch and the turned on second switch correspond to different positions. 
 
 
 
     
     
       2. The driving circuit as claimed in  claim 1 , wherein a switching sequence of turning on the first switches is inversed to a switching sequence of turning on the second switches. 
     
     
       3. The driving circuit as claimed in  claim 1 , further comprising:
 an adjustment unit, coupled to the light emitting element strings and the current sources, for adjusting the driving currents according to currents of the light emitting element strings. 
 
     
     
       4. The driving circuit as claimed in  claim 1 , further comprising:
 a plurality of switches, respectively coupled between the current sources and a ground voltage; and 
 a control unit, coupled to the switches, for controlling conduction states of the switches according to a pulse width modulation signal, so as to control the current sources to whether or not provide the driving currents to the light emitting element strings. 
 
     
     
       5. The driving circuit as claimed in  claim 4 , wherein the control unit comprises:
 a buffer, having an input terminal receiving the pulse width modulation signal, and an output terminal coupled to the switches; and 
 a resistor, coupled between the input terminal of the buffer and the ground voltage. 
 
     
     
       6. A backlight module, comprising:
 a plurality of light emitting element strings; and 
 a driving circuit, comprising: 
 a plurality of current sources, for respectively providing a plurality of driving currents; and 
 a current switching unit, coupled between the light emitting element strings and the current sources, transmitting the driving currents provided by the current sources to each of the-light emitting element strings in order for a plurality of periods equally divided in a time interval, wherein each of the driving currents is correspondingly and rotatably transmitted between the light emitting element strings over the plurality of periods, wherein the same light emitting element string receives different driving currents for two adjacent periods, and a light emitting brightness of each of the light emitting element strings are related to an average of the driving currents, 
 wherein the current switching unit comprises:
 a plurality of first switch groups, each of the first switch groups comprising:
 n first switches, having first ends respectively coupled the corresponding light emitting element string, wherein n is a positive integer; and 
 n second switches, having first ends respectively coupled to second ends of the first switches, and second ends respectively coupled to the corresponding current source, 
 wherein a second end of an i-th first switch of each of the first switch groups is coupled to a second end of an i-th first switch of the adjacent first switch group, i is a positive integer and 1≦i≦n, one of the first switches and one of the second switches are turned on, and the turned on first switch and the turned on second switch are switched by timing, and in different first switch groups, the turned on first switch and the turned on second switch correspond to different positions. 
 
 
 
     
     
       7. The backlight module as claimed in  claim 6 , wherein a switching sequence of turning on the first switches is inversed to a switching sequence of turning on the second switches. 
     
     
       8. The backlight module as claimed in  claim 6 , further comprising:
 an adjustment unit, coupled to the light emitting element strings and the current sources, for adjusting the driving currents according to currents of the light emitting element strings. 
 
     
     
       9. The backlight module as claimed in  claim 6 , further comprising:
 a plurality of switches, respectively coupled between the current sources and a ground voltage; and 
 a control unit, coupled to the switches, for controlling conduction states of the switches according to a pulse width modulation signal, so as to control the current sources to whether or not provide the driving currents to the light emitting element strings. 
 
     
     
       10. The backlight module as claimed in  claim 9 , wherein the control unit comprises:
 a buffer, having an input terminal receiving the pulse width modulation signal, and an output terminal coupled to the switches; and 
 a resistor, coupled between the input terminal of the buffer and the ground voltage. 
 
     
     
       11. The backlight module as claimed in  claim 6 , wherein the light emitting element strings are respectively a light emitting diode string.