Service Manual
9
2.2.3) High Voltage to Low Voltage Control Circuit :( fig.6)
T850
SPW-119
3
2
1
5
6
8
9
10
11
12
7
4
C847
1nF/50V X7R
Signal_GND
R842
499K
R853
27K
D841
NC/1N4148
R839
0.2R/1W FUSE
C849
0.01uF/50V X7R
U850
LD7552B
1
4
5
2
8
3
7
6
G
ND
RT
NC
COMP
OUT
VCC
VC
C
CS
C846
NC/47pF/50V X7R
Signal_GND
R843
499K
C854
68uF/450V
C875
472P
R859
0.75R/2W 1%
C860
332 Y 1
R856
10R
C872
NC/100P/1KV Y 5P
T851
NC
3
2
1
5
6
8
9
10
11
12
7
4
Signal_GND
R841
499K
D851
FR10-10
Signal_GND
R840
47R
D853
NC/P6KE170A
C848
1nF/50V X7R
R854
27K
R855
27K
R848
100K 1%
D852
SF10-04
Signal_GND
Q850
AP2762
2
1
3
R884
10K
-
+
D850
BL4-06
3
1
2
4
R844
47R
C855
10uF/50V
Signal_GND
fig.6
D850 is a rectifier in which there are 4 build-in diodes, inverting AC to DC.
C854 is used to smooth the wave from rectifier. R839 is a fuse resistor to protect the following
circuit when inrush current is too large. U850 is a highly integrated PWM controller. Typical
start-up current for U850 is only 30 uA, R841, R842 and R843 are serial circuit to limit current
flow. When current flow through R838 and R839 gets to Pin 3 of U850, with VDD
hold-up capacitor C855, U850 is enough for starting up.
When U850 begins to work Pin8 of U850 will output square wave to drive Q850, and then the
main current flow get to GND bypassing through T850, Q850. Because of the change of current
flow, wires in the other side of T850 will induct current. At the same time, the current inducted by
wires which connected T850 Pin 1 and Pin 2, with components of D852, R855, C855 and C849,
will be supplied to U850 for normal operating.
When the sense voltage across the sense resistor R859, reaches the threshold voltage around
0.85V, the output GATE drive will be turned off. Every time when the output of power supply is
shorted or over loaded, the FB voltage will increase, the build-in PWM output will then be turned off.
Both will prevent the power supply from being overheated under over loading condition. The PWM
duty cycle is determined by this current sense signal and VFB, the feedback voltage. When the
voltage on sense pin reaches Vcomp = (VFB-1.0)/3, a switch cycle will be terminated immediately.
Vcomp is internally clamped to a variable voltage around 0. 85 V for output power limit.
When Q850 are turned off, the main current flow will be consumed through D851, C875 R853 ,
R854 and R855. This will prevent Q850 from being damaged under large current impulse and
voltage spike.
2.2.4) DC_12V and 5V Output Circuit and Feedback circuit :( fig.7)
Содержание S1909WNf
Страница 1: ...Service Manual 0 Service Manual LCD Monitor S1909WNf ...
Страница 16: ...Service Manual 15 8 Key Parts Pin Assignments 8 1U105 TSUM1PEJ LF 2 ...
Страница 17: ...Service Manual 16 ...
Страница 18: ...Service Manual 17 ...
Страница 47: ...Service Manual 46 Attachment 3 PCB Layout power inverter bd power inverter bd Top Layer Bottom Layer ...
Страница 48: ...Service Manual 47 I F board Top Layer ...
Страница 49: ...Service Manual 48 Bottom Layer Power Keypad Top Layer ...
Страница 50: ...Service Manual 49 Bottom Layer OSD Keypad ...