Back Light Driver Units - THOMSON MT31AS Service Manual

Service manual of MT31AS
The Schematic diagram of secondary coil

5.2. Back light driver units

Back light driver units supply constant currents for LED in module. Constant current source is
designed as DC-DC power. It can realize the brightness of BL adjustable and self-protect by
appropriative BL driver IC. DC-DC unit is realized by L601, D601 and Q601. GATE outputs PWM
control signals to control Q601's work. L601 outputs to LED+ by charge and discharge in sequence.
And it promotes VLED outputting by Power to LED+, so as to illume the LED. Specific PWM signal
is generated by BL driver IC. The IC is controlled by BL_ON and DIM. The voltage will be promoted
when BL_ON is in high voltage level. LED- feedback is adjusted by DIM duty ratio lineally so the
brightness is adjustable. +12V_POWER is the supply for IC. The driver ability is set by the
periphery such as ISET and ISENSE. OVP watch the rise of LED+ by the bleeder to avoid the
damage caused by the immense rise of voltage when circuits work normally. LED 1,2,3,4 are LED-
watching the current of LED, and feedback to GATE driver signals to realize to constant current
drive.