Skyworth 84E99UD LCD TV power supply circuit principle and troubleshooting ideas (below) - Power Circuit - Circuit Diagram

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Industrial Router Crystal 3.2*2.5mm 3225 26M (26.000MHZ) 12PF 10PPM 20PPM 30PPM

One-piece inductor

4. The circuit diagram of the motherboard power supply DC-DC converter circuit is shown in Figure 5. IC7 (FSFR1700XSL) is a half-bridge LLC resonant converter integrated circuit with zero-voltage soft-switching technology; TR5 is a pulse transformer; C103 is a resonant capacitor (which forms LLC resonance together with the inductor in TR2); R143 is a current-limiting resistor; D35 (UF4007) is a bootstrap boost diode; C102 is a bootstrap boost capacitor; R104 is an overcurrent detection sampling resistor; R150, R151, R153 are sampling resistors; PC4 (FOD817) is a photocoupler; IC8 is a precision voltage reference Regulator IC; R148, C108 are used to prevent parasitic oscillations.

Basic working process: When the PFC circuit works normally, Q2 is turned on, and the PWM1 VCC voltage of Q2 output is sent to the 7th pin of IC7 to provide the working voltage. When the undervoltage lockout detection circuit inside IC7 detects that the voltage of input 7 is higher than the typical gate voltage of 12.5V, the undervoltage lockout detection circuit will output the enable control signal decorrelation circuit, and the voltage regulator circuit provides the relevant circuit. Operating Voltage. When the internal oscillation circuit of the IC73 pin is normally powered, the oscillation circuit starts to oscillate. The signal generated by the oscillation passes through the frequency divider, the delay device, the NOT gate, the electric translation phase/balance delay device, and the gate driver to the high end. The control gate of the low-end power switch tube, the half-bridge LLC resonant converter circuit starts to work, the primary 2-6 winding of the pulse transformer TR5 induces an electromotive force through the current, and each secondary winding senses a corresponding electromotive force, and is rectified and filtered to obtain 12V, 24V, thus achieving DC-DC conversion.

Voltage regulation working process: When the voltage of the 12V or 24V output is high, the high voltage is sampled by the resistor, the input voltage of IC8 rises, the output voltage decreases, the current passed by the internal LED of PC4 increases, and the phototransistor passes. When the current is increased, the feedback voltage obtained by the 2 pin of IC7 is lower than normal, the on-time of the switch tube is shortened accordingly, and the induced voltages on TR5 are correspondingly reduced, and the voltage at the output of 12V and 24V is restored to the normal value. When the voltage at the 12V or 24V output is low, the regulation process is reversed.

In-chip overvoltage protection process: When the 7-pin supply voltage of IC7 exceeds the typical gate voltage of 23.5V, the overvoltage protection circuit will start to control immediately, forcing the oscillator to stop oscillating, and the internal power switch can not be driven and is turned off. Thereby achieving overvoltage protection.
Overcurrent protection process: When the current of the power output loop is too large for some reason, this excessive current is sampled by R140, R139, C98 are integrated and fed back to pin 4 of IC7. As long as the 4 pin of IC7 is lower than 0.58V and the duration exceeds 1.5μs, the overcurrent protection circuit starts to control, the forced oscillator stops oscillation, and the internal power switch tube is turned off without a drive signal, thereby achieving overcurrent protection.

Overheat protection process: When the temperature of the power switch tube exceeds 130 °C, the overheat protection circuit starts to control, the forced oscillator stops oscillation, and the internal power switch tube is turned off without a drive signal, thereby achieving overheat protection.

U9 constitutes a 12V\24V overcurrent detection circuit.
The pin parameters of FSFR1700XSL are shown in Table 1.

5. The circuit diagram of the backlight-powered DC/DC converter circuit is shown in Figure 6. U1 (FAN7631) is an LLC control integrated circuit introduced by FAIRCHILD. TR1 /TR2/TR3 is a pulse transformer; C18/C19 is a resonant capacitor (which forms LLC resonance together with the inductance in TR1 /TR2/TR3); R10 is a current limiting resistor; D1 (UF4007) is a bootstrap boost diode; C10 is Bootstrap boost capacitor; R11 is overcurrent detection sampling resistor; R33, R32, R34 are sampling resistors; PC1 (FOD817) is a photocoupler; IC1 (KA431) is a voltage regulator integrated circuit with precision voltage reference; R20, C16 Used to prevent parasitic oscillations. U4, U5, and U6 are LLC secondary synchronous rectification driver ICs.

Basic working process: When the PFC circuit works normally, Q1 is turned on, and the PWM2 VCC voltage of Q1 output is sent to the 12 pin of U1 to provide the working voltage. When the internal oscillation circuit of the U12 pin is normally powered, the oscillation circuit begins to oscillate. The signal generated by the oscillation passes through the frequency divider, the delay device, the NOT gate, the electric translation phase/balance delay, and is sent to the high-end, low-end power. The control gate of the switch tube, the half-bridge LLC resonant conversion starts to work, the primary windings 2-6 of the pulse transformers TR 1 , TR2 , TR3 pass the current to induce the electromotive force, and the secondary windings sense the corresponding electromotive force, rectified, Filtering, 24V voltage is obtained, thereby implementing DC-DC conversion.
Voltage regulation working process: When the voltage of the 24V output terminal is high, the high voltage is sampled by the resistor, the input voltage of IC1 rises, the output voltage decreases, the current passed by the internal LED of PC1 increases, and the current passed by the phototransistor increases. Large, the feedback voltage obtained by pins 1 and 2 of U1 is lower than normal, the on-time of the switch tube is shortened accordingly, and the induced voltages on TR1, TR2, and TR3 are correspondingly reduced, and the voltage at the output of 24V is restored to normal. Value; when the voltage at the 24V output is low, the voltage regulation process is reversed as described above.

Second, the common troubleshooting process
1. 5V high/lower For 5V high/low fault, first check if the voltage feedback feedback circuit is normal (if necessary, disconnect PC3, judge a 3kΩ resistor on PC3's 3rd and 4th feet) ), then try to replace PC3 for judgment.
2. No PFC voltage For the failure of PFC voltage, you can first consider whether there is an overcurrent component, then check if the working condition of U3 is available, whether the PFC boost circuit is normal, and the 12/13 pin of U3 is output to the gate of switch Q 16/Q20. Whether the pole signal transmission loop is normal, check whether the external current and voltage feedback loops of 8, 9, 10, 15, and 16 are normal. Finally, consider replacing the U30.
3. PFC voltage is high/low. For PFC voltage high/low fault, first consider whether the input voltage is high or low. Then consider whether the 8-pin voltage feedback loop is normal. Finally, consider replacing U3.
4. 12V, 24V no output For 12V, 24V no output fault, first check whether there is standby control level over; secondly consider whether Q6, Q7 and related components are damaged, whether the oscillation capacitors C18, C9 are deteriorated, soldering, bootstrap capacitor Whether C10, D1, etc. are damaged; then compare and repair the secondary rectifier circuit components; finally consider replacing U1.
5. 12V, 24V high / low For 12V, 24V high / low fault, mainly check whether the feedback circuit components composed of IC1, PC1 are faulty.