Led Driver Circuit - Sony BVM-L230 Service Manual

2. FAN ON/OFF control
. ON/OFF operation is controlled using the output control
signals (FAN_ON and FAN2_ON) of an H8
microcomputer (IC6704). (At present, FAN_ON and
FAN2_ON are the specifications of simultaneous ON/
OFF control.)
. FAN_ON is the control signal (connector CN6401) of
one center fan. FAN2_ON is the control signal
(connector CN6403) of two side fans.
. The initial setting just after the power is turned on is fan
control OFF.
. ON/OFF operation and output voltage change are
controlled so that an H8 microcomputer (IC6704)
calculates a maximum panel temperature from the value
of a room temperature sensor and the value of a
temperature sensor on the S board and keeps the
temperature within 55dC.
3. Overvoltage and overcurrent protection
circuits
Outline
The DC-DC converter (IC6403) used for red LED and fan
power supplies has internal overvoltage and overcurrent
protection circuits. These protection circuits protect BVM-
L230 from the abnormal current due to the short-circuited
R_OUT and FAN_VCC output voltages and the abnormal
voltage due to the feedback circuit destruction of each
power supply.
Overvoltage protection circuit
This circuit stops each power operation in the latch state
when the voltage at the INV pin of a DC-DC converter
(IC6403) exceeds 0.95 V (output voltage +12%).
Overcurrent protection circuit
This circuit is monitored using the resistors (R6440 and
R6441) between the VCC pin of a DC-DC converter
(IC6403), and TRIP1 and TRIP2 pins. The DC-DC
converter (IC6403) stops in oscillation when red LED
power becomes approx. 2.4 A and when fan power
becomes approx. 1.5 A. Power operation stops in this
case.
BVM-L230

2-3-2. LED Driver Circuit

LED is driven by controlling a LED driver (IC6502 to
IC6513, TLC5941) using an H8 microcomputer (IC6704).
The data signal (SIN/SOUT) of a LED driver is connected
in series to each LED driver with the H8 microcomputer
(IC6704) as a starting point and data is output in series
from the microcomputer.
A blanking signal is generated and distributed using CPLD
(IC6900) and supplied to each driver circuit (BLANK_A
to BLANK_M), in consideration of the blank port of an H8
microcomputer (IC6502).
1. Outline of CPLD circuit
Functions
. GS clock (LED driver PWM control reference clock)
generation
. Blanking control
. Blanking signal generation and distribution
. Latching of LED driver errors (XERR: Open error and
temperature defect)
Function details
. GS clock (LED driver PWM control reference clock)
generation
This function frequency-divides and generates the supply
clock (CLK_H8OUT input clock at pin 37) of an H8
microcomputer (IC6704). (A GSCLK_OUT clock at pin
10 is output.)
A frequency-division ratio is determined as described
below by two bits D0 and D1 (input data at pins 34 and
35) set using an H8 microcomputer (IC6704).
D0 = L, D1 = L: 1/4 frequency division
D0 = H, D1 = L: 1/2 frequency division
D0 = L, D1 = H: 1/8 frequency division
Default setting is 1/2 frequency division. A frequency is
16.384 MHz.
. Blanking control
This function outputs a blanking signal by setting the
control signal (BL_CTRL_X input signal at pin 31) from
an H8 microcomputer from low to high.
. Blanking signal generation and distribution
This function generates a blanking signal (4096CLK) for
each LED driver from the generated GS clock. In this
case, distribution signals (BLANK_A to BLANK_M)
are output with 4096/16 GS_CLK shifted so as to reduce
radiation.
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