Changhong ITV46920DE LED LCD TV Backlight Driver Circuit Overview
The following diagram illustrates the LED backlight driver circuit in the Changhong ITV46920DE LED LCD TV. Each section of the circuit is identical and operates independently, driving a group of LED lamps. The driver circuit provides an output voltage of 170V at 90mA. Similar to the backlight circuits found in Hisense models, this system uses the integrated IC HV9911NCJ, which functions as a high-efficiency LED driver. This IC includes features such as single-switch drive control, high-side current sensing, closed-loop current regulation, high PWM dimming capability, internal linear regulator (9V to 250V), constant frequency or constant off-time control, VDD = 10V short-circuit protection, overvoltage protection, synchronization lock, programmable MOSFET current limit, and soft start functionality.
When the power supply transitions from standby to normal operation, the 130V DC voltage is divided by resistors R9006, R9005, and R9004, creating a 2.47V signal on R9004. This activates ZDT9001, allowing 12V to flow through R9011 and R9010, resulting in 11.25V on R9010H. This voltage turns on Q9002, enabling the 12V to reach the first pin of the HV9911NG IC, which powers up the driver module.
Meanwhile, the BL_ON signal from the signal processing board is divided by R9013 and R9003, generating a 0.56V signal that turns on Q9003. This causes Q9004 to turn off, allowing +5VS to reach the 13th pin of multiple ICs, including IC9201, IC9301, etc. Once powered, the internal oscillator of IC9101 begins generating pulse signals, which are then sent to the base of Q9102 and Q9103.
The internal reference voltage of 2.4V from HV9911NG is applied to pin 15 via R9107. The frequency setting resistor R9105 adjusts the oscillator frequency, ensuring stable operation once set.
The drive signal from pin 3 of HV9911NG is amplified by Q9012 and used to drive Q9101. When Q9101 is on, energy is stored in inductor L9101, creating a voltage spike when it turns off. This spike charges capacitor C9110 through D9101 and D9105, resulting in a 170V/90mA DC output for the LED strip, via R9128 and R9129.
A bleed circuit composed of Q9103 and D9102 ensures that any residual charge on Q9101's gate is discharged during the off period, preventing damage due to charge accumulation.
An overcurrent protection circuit involving R9602, R9603, and the 5th pin of HV9911NG detects abnormal currents through Q9101. If the current exceeds safe limits, the IC stops the drive signal, protecting the switching transistor.
The brightness adjustment circuit uses VR9001 and ICM9001 to control the current setting pin (pin 15) of the driver IC, adjusting the duty cycle of the output pulses to regulate backlight brightness.
The current stabilization circuit, using Q9104 and R9121, monitors the LED current and adjusts the pulse width to maintain a consistent current level. Overvoltage and overcurrent protection circuits ensure safe operation under abnormal conditions, shutting down the system if necessary.
This comprehensive design ensures efficient and reliable LED backlighting in the Changhong ITV46920DE model.
Switch Cabinet,Innovative Low Voltage Switchgear Cabinet,Switch Rack Cabinet,Switch Cabinet Wall Mount
Tianhong Electric Power Technology Co., Ltd , https://www.tianhongtransformer.com