Shulou(Shulou.com)06/03 Report--

This paper briefly introduces the working principle of Inverter:

Inverter is a DC-to-AC (DC to AC) transformer, which, as its name implies, is a reverse voltage conversion. Compared with the power adapter Adapter, it is actually a process of voltage inversion. The power adapter converts the 220V AC voltage of the municipal power grid into a stable DC output, such as 5V DC supplied by USB, while the inverter converts the DC voltage output of the power adapter into high-frequency high-voltage AC. Current inverters generally use PWM (Pulse width Modulation) technology to obtain high-power and high-efficiency AC inverter output.

Block diagram of Inverter working principle

Input interface section:

The input part usually has three signals, 1) DC input voltage, 2) working control voltage, 3) Panel current control signal. The DC input voltage is provided by the DC output of the power adapter or the power board, and the working control voltage is provided by the control chip on the motherboard, which is 0 or 3V. When the working control voltage is 0, the inverter does not work, but when the working control voltage is 3V, the inverter is in normal working state. The voltage of the current control signal is provided by the motherboard, which varies from 0V to 5V, which is fed back to the feedback end of the PWM controller through different current control signal values. The inverter provides different current to the load. The smaller the current control signal value is, the greater the output current of the inverter is.

Voltage start circuit:

The working control voltage is high, and the output high voltage is used to light the LCD Panel backlight tube.

PWM Controller:

It is mainly composed of the following parts: internal reference voltage, error amplifier, oscillator and PWM, protection circuit, output transistor.

DC conversion:

The voltage conversion circuit is composed of the MOS switch tube and the energy storage inductor. The input pulse is amplified by the amplifier and drives the MOS tube to do the switching action, which makes the DC voltage charge and discharge the inductor, so that the other end of the inductor can get the AC voltage.

LC oscillator and output circuit:

Ensure the 1500V voltage needed for the lamp to start, and reduce the voltage to 800V after the lamp is started.

Output voltage feedback:

When the high voltage lamp is working, the sampling voltage is fed back to stabilize the voltage output of the inverter.

The inverter transformer is generally multi-input and one high-voltage output. For the LCD Panel with multiple lamps in the large-screen TV, multiple inverter boards or multiple inverters are generally used to output separately. For inverters, due to the high voltage generated during their work, internal inverter transformers, PCB, output sockets and so on, many customers require the use of materials and components approved by UL or corresponding fire-resistant grades in the production process to ensure the safety of their products.

At present, during the implementation of compulsory product certification in China, the safety assessment of inverter mainly includes the following aspects:

1) temperature rise

When the inverter is working normally and a single fault occurs, the internal inverter transformer, PCB board and other components will not have too high temperature that affects the personal safety or the normal operation of the surrounding devices.

2) Fire prevention requirements

Check whether the internal components which are easy to produce high temperature, such as internal inverter transformer and PCB board, have a certain fire grade and ability to ensure that they will not have fire hazard, and the ability to slow down and stop the spread of flame when other components catch fire.

3) Electrical strength

Check whether the high voltage generated by the inverter will affect the low voltage input part and the safety of the user due to the insufficient insulation of the inverter transformer.

4) current limiting circuit

Because the inverter is a component that produces high voltage and at the same time supplies power to the lamp tube of the LCD panel, the user can contact the surface of the LCD screen. In case the LCD screen is damaged, the user may be exposed to the high voltage generated by the inverter. In this case, the output voltage can not be reduced directly, so it is necessary to limit the output current of the inverter to ensure the safety of the users. in the product safety test, it is particularly important to check according to the requirements of the current-limiting circuit. If the product is submitted to the inverter of the same specification, it is also necessary to test the current-limiting circuit of the reported inverter.

The above safety inspection items are only a basic requirement for the product. through a simple analysis of the working mode and principle of the inverter, we can have a simple understanding of its safety performance, better master the correct method of use, and avoid danger. let home appliances better serve us and improve our quality of life.

Principle

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