Sony HS75, Service Manual, Page: 36 / 64

HS75 Sony
36
b. Inverter
Input interface section:
1.12V DC input, offered by power section; 2. ON/OFF enable signal,
offered by MCU in the main board with its value of 0V or 5V. When OFF=0V,the inverter doesn’t work, while
OFF=5V, it works under normal situation. 3. DIM signal for luminance modulation, offered by GM5321 in the
main board with its range of 0~5V. The Inverter offers different currents to the loads because of the different
feedback of voltage to the feedback-terminal of PWM. The smaller the value of DIM, the smaller the current
output of Inverter, the darker the brightness.
Voltage start-up circuit:
It consists of a NPN transistor and a NMOSFET with two working stages.
The first stage: When the ON/OFF enable voltage is 0V, the Q807 is closed, Q806 gets through, the voltage
of drain pulled down, so U801 doesn’t work. The second stage :ON/OFF is high level, Q807 gets through,
Q806 breaks off, Hence U201 produces pulse output to control switch transistor, and the Inverter which
applied high voltage across the backlight works well.
Q807
DTC144WKA
+5VDD
U
801
OZ9
RRB
1 2 3 4
5 6 7 8
ENA_SST CT GNDA DRV2
DRV1
VDDA
VSEN_DIM
ISEN
Q806
RK7002
R
827
1M
C
840
0.1uF
R821
82K
ON/OFF
C
817
N
C