Inverter is a DC to AC transformer, it is actually a voltage inverter process with the converter. The converter converts the ac voltage of the power grid into a stable 12V dc output, while the inverter converts the 12V dc voltage output from the Adapter into a high-frequency high-voltage alternating current. Both parts also adopt the pulse width modulation (PWM) technology which is used more often. The core part is a PWM integrated controller, Adapter USES UC3842, inverter USES TL5001 chip. The operating voltage range of TL5001 is 3.6~40V, and it is equipped with an error amplifier, a regulator, oscillator, PWM generator with dead zone control, low voltage protection circuit and short circuit protection circuit, etc.
Input interface: the input part has 3 signals, 12V dc input VIN, working enable voltage ENB and Panel current control signal DIM. The VIN is provided by Adapter, and the ENB voltage is provided by the MCU on the motherboard. Its value is 0 or 3V. When ENB=0, the inverter does not work, while when ENB=3V, the inverter is in normal working state. DIM voltage is provided by the main board, and its variation range is between 0 and 5V. When different DIM values are fed back to the feedback end of PWM controller, the current provided by the inverter to the load will also be different. The smaller the DIM value is, the greater the current output by the inverter will be.
Voltage starting circuit :ENB is at high voltage,
Inverter (FIG. 2)
Inverter (FIG. 2)
Output high voltage to light the Panel backlight lamp tube.
PWM controller: has the following functions: internal reference voltage, error amplifier, oscillator and PWM, overvoltage protection, undervoltage protection, short circuit protection, output transistor.
Dc transformation: the voltage transformation circuit is composed of MOS switching tube and energy storage inductance. The input pulse is amplified by push-pull amplifier to drive the MOS tube to do switching action, so that the dc voltage can be charged and discharged on the inductance, so that the ac voltage can be obtained at the other end of the inductance.
LC oscillation and output loop: ensure the 1600V voltage required for the lamp tube to start, and reduce the voltage to 800V after the lamp tube starts.
Output voltage feedback: when the load is working, feedback sampling voltage to stabilize the voltage output of I inverter.