Introduction, working principle and main components of inverters

An inverter is a power conversion device that converts 12V or 24V direct current (DC) into 230V, 50Hz alternating current (AC) or other types of AC power. The output AC power can be used by various types of equipment, meeting the AC power needs of users in mobile power supply locations or off-grid areas to the greatest extent.

Also known as an inverter power supply, this device enables the use of DC power sources (like batteries, switching power supplies, fuel cells, etc.) to be converted into AC power, providing stable and reliable electricity for appliances such as laptops, mobile phones, handheld PCs, digital cameras, and various instruments. Inverters can also be used in conjunction with generators, effectively saving fuel and reducing noise. In the fields of wind and solar energy, inverters are indispensable.

Small inverters can utilize the power from automobiles, ships, or portable power supply devices to provide AC power in the field. Inverters have a wide range of applications. They can be used in various means of transport, such as automobiles, ships of all kinds, and aircraft. In solar and wind power generation, inverters play an indispensable role.

Working Principle of Inverter

An inverter is a DC-to-AC (Direct Current to Alternating Current) transformer. As the name suggests, it transforms voltage in reverse. Essentially, it performs a voltage inversion process opposite to that of an adapter (Adapter). While an Adapter converts AC voltage from the mains grid into a stable 12V DC output, the Inverter converts the 12V DC voltage from the Adapter into high-frequency, high-voltage AC. Modern inverters typically employ PWM (Pulse Width Modulation) technology to achieve high-power, high-efficiency AC inversion output.

Main Components

1. Input Interface Section

The input section typically processes three signals:

1. 12V DC Input Voltage: Supplied by the DC output from an Adapter.
2. Operation Control Voltage: Provided by the control chip on the mainboard, valued at 0V or 3V.
   • When control voltage = 0V, the inverter stops working.
   • When control voltage = 3V, the inverter operates normally.
3. Panel Current Control Signal: Generated by the mainboard, with a voltage range of 0–5V.
   • This signal is fed back to the PWM controller's feedback terminal.
   • Lower current control signal values result in higher output current from the inverter.

2. Voltage Startup Circuit

When the operation control voltage is at a high level (3V), this circuit outputs high voltage to ignite the backlight lamp of the Panel.

3. PWM Controller

Comprises the following functional blocks:

• Internal reference voltage
• Error amplifier
• Oscillator and PWM generator
• Overvoltage protection (OVP)
• Undervoltage protection (UVP)
• Short-circuit protection (SCP)
• Output transistors

4. DC Conversion Circuit

Consists of MOS switching transistors and an energy-storage inductor, forming a voltage conversion circuit.

• Input pulses are amplified by a push-pull amplifier to drive the MOS transistors.
• Switching actions of MOS transistors charge/discharge the inductor, converting DC into AC voltage.

5. LC Oscillation and Output Circuit

• Generates 1500V to ignite the lamp during startup.
• Reduces voltage to 800V after lamp ignition for stable operation.

6. Output Voltage Feedback

When the load operates, the feedback circuit samples the output voltage to stabilize the inverter's voltage output.

Multi-Output Design for Large-Screen Applications

Inverters typically feature multiple input channels and a single high-voltage output. For LCD panels with multiple backlight lamps in large-screen TVs, manufacturers generally use either:

• Multiple inverter boards, or
• Separate inverters for independent outputs.

Safety Certification Requirements

Since inverters generate high voltages during operation, materials and components (e.g., inverter transformers, PCBs, and output sockets) must comply with safety and fire-resistance standards. Key safety certifications include:

1) Temperature Rise Test

Verifies that during normal operation or under single-fault conditions, temperatures of internal components (transformers, PCBs, etc.) will not:

• Endanger personal safety, or
• Disrupt adjacent device functionality.

2) Fire Resistance Requirements

Ensures high-temperature components (transformers, PCBs, etc.) possess adequate fire-resistance ratings to:

• Prevent self-ignition, and
• Slow/block flame propagation from external fires.

3) Electric Strength Test

Evaluates whether high-voltage output (generated during operation) could compromise insulation of the inverter transformer, causing high-voltage leakage to low-voltage input circuits and endangering users.

4) Current-Limiting Circuit Test

Critical safety measure since users may touch the LCD surface. If the screen cracks, users risk exposure to inverter-generated high voltage. When voltage reduction isn’t feasible, current-limiting circuits restrict output current to protect users.

• Note: If inverters from different manufacturers are used in a product, additional current-limiting circuit tests are mandatory.