After the supply voltage rectifier, the interior of the leak pipe pin 7 of the power applied to the end feet of primary end pin 2 of the transformer, rectifier bridge, city, a standby power supply circuit: 220V AC power into the TV, directly added to the D895 meanwhile single-phase rectifier circuit 300V voltage, added to the standby power supply T880 P2 after T880 winding ----7 P1 -- standby IC851 ------IC power switch very D in IC 5 feet, there is a low voltage VDD power supply generating circuit in switching power supply start-up phase IC7 feet into the high impedance circuit for the power supply VDD power supply circuit, the current is very small, only in the IC oscillation circuit power supply. The power supply circuit produce a power supply voltage of 6V is 5 feet to VDD, for oscillations within the IC, driving power supply circuit, driving 7 feet in the high power switch tube into the repeated ----- ----- open -- state. IC 4 pin is the source of the high power switch tube, the ground. Following current is generated when the IC switch tube conduction: current from the cathode of D895 starting at the foot of the ------T880:P2---------------P1----------IC851:7-----------4 ------- to ground. The current flowing through the transformer T880 primary coil, the coil the current into a magnetic field, the energy in the form of magnetic energy stored in the T880. This current is an initial value of 0 and a linear increase of the current. During the switching of the switch, the transformer secondary coil S1 is negative, the S2 is positive, and the reverse is added to the D891 and D893 ends of the rectifier tube, the tube ends. That is to say when the high power switch is on, the power of the city can be stored in the transformer.

Second, when the high power switch tube by conduction into cut-off, storage in the transformer of electric can be released to the load. At the same time, the secondary coil of the transformer S1 end is, S2 terminal is negative, positive and in the rectifier tube 891, both ends of the d892, rectifier conduction, to the C865 C864 charging. 18.5V standby voltage. The voltage is divided into three paths: the first circuit is applied to the constant voltage sampling circuit. Second way to the DC-DC transform circuit IC852 1 pin, the 18.5V power supply voltage converted into 7V standby voltage SBT7V. CPU circuit for A board. Third added to switch the S pole of Q843, G pole from CPU turn-on voltage control, from d very output controlled 18.5V power, added to a plate of audio power amplifier circuit.

Three, V1-V2 T880 coil, is the feedback loop, V2, V1 D870 filter, C848 filter, get the 20V voltage, added to the 3 IC851 VCC. In the IC, the VCC voltage starts at 5 feet of the VDD power supply, while the IC is cut off from the 7 pin for the VDD power supply. The pulse voltage of the V1 terminal, also after R850, is added to the IC's 2 foot, the trigger and the synchronous IC oscillation circuit to drive the switch on and off of the switch. The role of R850, R851, C868 is to make sure that the electric energy of the T880 can be released into the next cycle, which is called a quasi resonant circuit. This can minimize the conduction loss of the switch tube.

Four, error sampling and voltage regulator control circuit: T880 secondary rectifier output voltage of 18.5V, first applied to the partial pressure sampling circuit, series resistance R879, R877, R892, R897 component voltage sampling circuit. Voltage at the share of the upper end of the R892, added to the error amplification IC890 input ref and normal voltage on this pin should be 2.48V, IC890 conduction, produce the following current: voltage 18.5V cathode -------R880-------- optocoupler PC880 luminotron --------IC890 K end -------A end -- to. The current the optocoupler LEDs. When the voltage is increased by 18.5V, IC890 the input end of voltage is also an increased, resulting in the current increases, the optocoupler luminous tube luminescence intensity, photosensitive tube resistance becomes smaller, the r852 will enable IC851:1 pin voltage is decreased, which will enable the switch tube conduction width decreases. T880 storage can become less and eventually make 18.5V with a constant voltage. Here, it is necessary to talk about Q883: P in P3 row in the 13 feet, is from a board CPU output power command SUBON, boot time, voltage of this pin for 2.25V. By added to the R896 Q883 B, the tube conduction, the R897 short circuit, so that the R892 at the upper end of the pressure drops and IC890 conduction current, optocoupler light-emitting light-emitting diode dimming, photosensitive tube resistance increases, the IC851:1 pin voltage increased, switch tube wide versatility, value at a standby voltage output voltage is 18.5V. And when is the low level 0V from a CPU board SUBON, cut-off Q883, R897 no longer is short circuit, which will make at the upper end of the R892 partial pressure increased, the conductance IC890 through current and the standby voltage output down to 10V.

Fifth, standby power supply high power switch tube D peak absorption circuit: IC851 switches off. T880 primary coil will produce a very high voltage spike, added to the IC851:7 feet, namely high power switch tube d very, the high peak voltage will breakdown switch tube. To this end, a peak voltage absorption circuit is connected at both ends of the primary coil of D892, T880, R873, R886, C889. When these parts failure or open circuit, it can not absorb the peak voltage, so that the breakdown of IC851.

Six, under voltage detection circuit, when the city electricity 220V power supply voltage drops too low, because voltage stabilizing circuit of automatic regulation, in order to maintain a constant voltage output switching power supply, the switch tube conduction through the wide, current is too large, will damage the power switch block. So the design of the City Power undervoltage protection circuit. Composed D885 c888 City Electric half wave rectifier circuit, when the city electricity is 220V, c888 voltage is 300V, after R884, R888, r894 pressure. In r894 share voltage 88V. This voltage is applied to the second voltage regulator tube D884, d882. The two voltage stabilizing tube breakdown conduction. Q882 along with conduction, Q882 C pole to 0V, lead to stop Q850, Q850 of C electrodes of the are connected with the foot of the IC851:1. E very grounding, cut-off Q850, the normal work of the IC851 no effect. When the city electricity voltage drop is excessive, such as lower than the AC 100V, r894 pressure drop, voltage regulator tube D884, cut-off d882, Q882 subsequently cut-off, 6V voltage IC851:5 feet, added to the R854 Q850 B, Q850 conduction of the, the grounding pin 1 of IC851, IC851 to stop work, protection switching power supply circuit from being damaged. D857 a regulator tube, connected in IC851 1 foot to ground, is a protection voltage regulator tube, prevent voltage optocoupler does not work, the output voltage is too high. When the voltage regulator tube breakdown, leakage, reverse resistance, will cause the IC851:1 pin voltage drops, causing the switch power supply output voltage drop. Must pay attention in the maintenance.

Seven, from a CPU board boot high level commands, also added to the Q881 B, the tube conduction, C is very low level, after r818. Added to the switch tube Q843 g, Q843 is a p-channel MOS transistor, when G is extremely low electricity at ordinary times, the tube conduction, the output voltage 18.5V, added to a plate with audio power amplifier circuit. When the normal work, Q882, Q850 IC851 1 pin voltage is 1.7V2:3V3:20V5:6VD882D884 in kind is the two resistance, rather than the regulator tube. D891 output standby power supply voltage, in the normal boot, is the 18.5V voltage, while in standby mode is the 10V voltage. In normal boot, the REF IC890 is 2.48V, K is B 17V.Q881Q883 is 0.6V.

Eight, a main switch power supply circuit: City electric voltage 220 into TV P plate, after the control of power relay RL801, input applied to the rectifier bridge d802, C830 C842 for filtering, 300V voltage, is added to the main power switch transformer T801 P2 pins, through the primary coil of the internal, through the P1 pins and pin 1 of IC830, IC830 is main switching power supply integrated block, pin 1 is internal power switch tube D. 2 pin is the S pole of the switch tube. 3 feet is the ground of IC830. At one end of the input of the 220V current, after a R802 start resistor, the IC830 is applied to the 4 pin, which provides the power supply voltage for the starting phase of the oscillation circuit within the IC830. Inside the switch tube in under the action of the driving pulse, repeated open - closed - -- on -- off, switch tube conduction. D, which is a very current and end through the switch transformer primary coil P1---P2, the city power electrical energy stored in the transformer, and when the cut-off switch, pressure regulator through the secondary coil, the power supply to the load. The pulse voltage of the secondary coil S1----S2, D810, C815, C814 filter, 24V voltage, the power supply to the inverter. V1---V2 coil is the feedback loop, the V2 is connected to the ground, the pulse voltage of the V1 terminal, the R833 is added to the D833 cathode, after rectification, C833 filtering, to get the 20V voltage, IC830 4 pin power supply 20V. V1 end of pulse voltage, also after R833----D840----R846----D843---- added to IC830:7 feet, when to load release finished before the control switch in the IC830 tube into the next cycle through transformer in electric energy. In order to reduce the opening loss of the switch tube. Within the IC switch tube conduction, tube to the S pole of the current switch, through 0.15 euro, 0.12 European resistance R843, R844, pulse voltage generated in a resistor, the R845 is applied to the IC pin 5, when the switch current is too large, added to the 5 foot pulse voltage is too high, IC will start overload protection, limit switch tube current value.

Nine, the main switch power supply voltage: D810 output of the 24V voltage, added to the IC811 1 feet, IC811 is a partial pressure sampling and error amplifier integrated circuit. The output end of 2 feet to control the luminous intensity of the luminous tube voltage PC841 optocoupler. When the switch power supply output 24V voltage increases, IC811 pin 2 of the voltage drop, optocoupler in light emitting diode luminescence intensity, a photosensitive tube variable resistance and small, a photosensitive tube e very output voltage increases, IC830:6 pin voltage is increased, the control switch tube conduction width, 24V output stable invariant. Is the primary coil peak voltage absorbing circuit d832, R832, R831, c831, when the switch tube by conduction was suddenly transformed into cut-off, the primary coil will produce very high peak voltage, breakdown within the IC switch tube, increase the peak absorption circuit, you can avoid this problem.

In nine, the switch of the main switching power supply control circuit: from a CPU board power instruction: SUBON high level and added to the Q822 B pole, Q822----Q820 subsequently conduction, power relay RL801 line package with 5V voltage, the line package pull, two 220V contact action closure, 220V, add to rectifier bridge, the main switching power supply to work. When the main switch power supply works, IC830's 4 foot voltage: 20V. 6 feet: 1.4V7:1.4V5:0.07V. IC811's 1 foot: 24V2 foot: 22V.

Ten, the power board of the separate maintenance: when the TV failure, it is possible that the motherboard is bad, it is also possible that the P board is caused by bad power supply board. Some of the soft fault is difficult to distinguish what is the cause of the board is not normal. Therefore, it is necessary separate detection power board, the P plate is removed from the machine, to the plate P alone and 220V power supply and the 24V power supply output terminal connected to the dummy load lighting 100W, if the boot, P in the output of the various power voltage is normal, P board is good, the fault is caused by a plate. The method is as follows: the P3 12 pin and 13 pin an 5K resistor, the P1 connected to the 220V. The standby power supply and the main switch power supply can be entered into the working state at the same time. At this point to measure the voltage of the P3 and P2 are normal.