Dell E2009W Manual de servicio - Página 9
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The over-voltage protection feature is implemented by using an extermal capacitor
devider(C1/C15/C16/C17) to sense the output voltage.The divide-down voltage signal is sent to the IC
Pin1(VSEN) ,thus regulating the output voltage.
If a CCFL is removed, fails or damaged during normal operation, CCFL current is no longer sensed and
the voltage on ISEN pin drops. The voltage at the SSTCMP(pin2)rises rapidly because there is no current
feedback at ISEN(pin14).When the voltage at SSTCMP reaches a threshold of approximately 2V and ISEN
is less than 0.7V,a current source charges the capacitor(C3) connected to TIMER(pin12).Once the voltage
level at the TIMER pin reaches a threshold of approximately 3V,the drive outputs shut down and latch.To
resume operation,toggle the ENA signal or restart VDDA.
Over-voltage and over-current protection are monitored by the voltage on VSEN(pin1).During normal
operation,if a CCFL is damaged or removed,the voltage at VSEN exceeds the user-defined, preset voltage
set by OVPT(pin15),the driver output duty cycle is regulated and the shutdown delay timer is
activated.OVPT sets the overall protection threshold voltage that is lower than3V(VSEN threshold. Once
the voltage at TIMER pin reaches 3V,the IC will shut down and latch. OVPT voltage setting is determined
by a resistor divider(R16/R8)connected to the OVPT.
2.2.Power PWM circuit
2.2.1 AC Input and EMI Filter:(fig.2.2.1)
CN850
2
CN850 is a connector for connecting AC Power. F850 is a fuse to protect all the circuit AC. Input
voltage is from 90V to 264V. R850,R851and R852 are joined between two inputting main circuit to
prevent man from shock. L850 is used to clear up low frequency wave. C850 and C851 are used to
discharge the waves that L850 produced. High frequency waves are damped by C852.
2.2.2 High Voltage to Low Voltage Control Circuit:(fig.2.2.2)
4
-
F850
RT850
3.15A 250V
5R4A
C850
222 Y 2
10A/250V
C851
222 Y 2
D850
GBU4-06
R862
0.2R 1W Fuse
+
1
C854
100uF/450V
R842
Signal_GND
499K
R843
499K
C849
0.01uF/50V X7R
3
VCC
OUT
U850
LD7552B
5
NC
RT
C846
47pF/50V NC
2
COMP
CS
C848
1nF/50V X7R
Signal_GND
C852
0.47uF X2
fig.2.2.1
R841
R853
499K
C875
27K
472P
R854
27K
R855
27K
R856
D852
10R
C855
SF10-04
10uF/50V
Signal_GND
R844
47R
8
D841
Q850
1N4148
AP2761
R848
4
100K 1%
2
Signal_GND
R884
10K
6
R840
47R
C847
1nF/50V X7R
Signal_GND
8
Service Manual
R850
499K
R851
499K
R852
499K
T850
D853
SPW-115
NC/P6KE200
.
1
3
D851
FR10-10
5
.
6
.
C860
332 Y 1
R859
0.43R/2W 1%
L850
CHK-007
11
12
7
8
9
10