| 摘要 |
<p>A liquid crystal display comprises a liquid crystal panel illuminated by a backlight unit BLU, the backlight unit comprising a plurality of LED strings RS1 to RSm. Each of the LED strings is connected to a DC power source 120 which supplies voltage Vout to the LED strings. The lowest cathode (i.e. at positions Dn) of each LED string is connected to a transistor (e.g. T1,Tm) collector electrode. Transistor emitter electrodes are connected to monitor resistors (e.g. R1,Rm), whilst base electrodes are connected to first pins (e.g. Ch1, Chm) of an LED driver unit 130. The LED driver unit is controlled by controller 135 and has second pins (e.g. Cm1,Cmm) connected between the transistor emitter electrodes and the monitor resistors. Accordingly, each LED string is connected to the LED driver unit by only two connections. The LED driver unit 130 comprises driving signal outputs OP1, OPm for supplying driving signals to each LED string. It also comprises LED short-sensing portions OPP1, OPPm for detecting short-circuits in LED components by comparing the transistor base electrode voltage with a reference voltage ref. Alternatively, a short may be determined by comparing the difference between a first sensing voltage (at Ch1) with a corresponding sensing voltage for the neighbouring LED string (at Chm). If a short is detected, the LED driver may disable either a particular LED string/channel or alternatively all LED strings may be turned off, e.g. by disabling the LED driver and the DC power source. The arrangement provides LED short-circuit detection with reduced manufacturing costs since only two LED driver connections are required per LED string. It also provides for LED backlight protection in the event of LED short-circuit defects, by switching off the affected LED string or the whole backlight unit, thus protecting remaining LEDs from overcurrent damage.</p> |
