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3
G input
4
Ground
5
Dark current detection output
6
Power supply
7
R cathode output
8
G cathode output
9
B cathode output
2.10 Analysis of power switch circuit
A typical self-excited pulse power switch has been chosen for this TV receiver. When the power
switch is in the ON position, the voltage from AC 220 V power grid will be rectified by a rectifying tube
VD810 to produce a pulse voltage , which will be filtered by a capacitor C806 220u to form a DC
voltage of about+300V, and the said DC voltage will be fed into the (1) of the power integrated circuit
N801 KA5Q1265RF-YDTU entry by the (1) (4) windings of switch transformer T801 BCK-100-02 ;
At start-up, the voltage from an AC single-phase power supply will be divided by starting resistors
R803 and R802 to provide starting voltage to N801. After start-up, an impulse voltage produced by
(6) (7)windings of T801 will be rectified and provided. Photo coupler N802 PC817C entry serves the
function of voltage regulation. The error message about the voltage exported by the switch
transformer will be transmitted to the (4) of N801by the photo coupler N802, hence adjusting the
oscillation parameters of N801.
During stand-by time, POWER signals will be at a lower level, which causes the triode V803
KSC815 to stop. So a voltage+12V will be put into the photo coupler N802 PC817C entry by
resistor R849 and diode VD816, which feeds a special parameter to the (4) of N801 and makes the
N801 enter a quasi-resonance working state, with the power supply voltage (3) being 11V 12V. In
this way, the output voltage of the switch transformer T801will drop a great deal, resulting in a great
reduction of stand-by power consumption.
The impulse voltage sent out by the (8) of the secondary of switch transformer will be rectified and
filtered by VD805 D5L60 and C816 100u to produce a DC voltage +130Vfor power supply to line
output electrode;
The impulse voltage sent out by the (13) will be rectified and filtered by VD807 D6L20U and C820
2200u to produce a DC voltage +15Vfor power supply to sound amplification circuit.
The impulse voltage sent out by the (11) will be rectified and filtered by VD806 TR5GU41 and C818
2200u to produce a DC voltage +12Vfor power supply to secondary power supply.
The DC voltage +8V sent out by the (8) of N804 after a voltage regulation of secondary power supply
will supply power to N201 decoding circuit, the DC voltage +3.3V obtained by the voltage regulation
of 12V by the resistor R843 2K , triode V801 KSC815 and diode DZ808 MTZ3.9B will supply
power to N201 micro-processing circuit, and the DC voltage +5V sent out by the (9) will supply power
to a storage block N202 KS24C08 circuit.
2.8
7.6K
0
0
4.9
3.1M
182.6
34.2K
97.6
1.4M
100.1
1.4M
93.4
1.4M
39
Circuit Explanation
7.4K
0
2.7M
28.2K
2.6M
2.6M
2.6M
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