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How the inverter works


Input interface part:
The input part has 3 signals, 12V DC input VIN, working enable voltage ENB and Panel current control signal DIM. VIN is provided by the Adapter, and the ENB voltage is provided by the MCU on the motherboard, and its value is 0 or 3V. When ENB=0, the Inverter does not work, and when ENB=3V, the Inverter is in normal working state; and the DIM voltage is provided by the motherboard. Its variation range is between 0~5V. When different DIM values ??are fed back to the feedback terminal of the PWM controller, the current provided by the inverter to the load will also be different. The smaller the DIM value, the larger the current output by the inverter.

Voltage start circuit:
When ENB is high, it outputs high voltage to light the panel's backlight tube.

PWM controller:
It has the following functions: internal reference voltage, error amplifier, oscillator and PWM, over-voltage protection, under-voltage protection, short-circuit protection, output transistor.

DC conversion:
A voltage conversion circuit is composed of a MOS switch tube and an energy storage inductor. The input pulse is amplified by a push-pull amplifier to drive the MOS tube to switch, so that the DC voltage charges and discharges the inductor, so that the other end of the inductor can get an AC voltage.

LC oscillation and output circuit:
Ensure the 1600V voltage required for the lamp to start, and reduce the voltage to 800V after the lamp is started.

Output voltage feedback:
When the load is working, the sampled voltage is fed back to stabilize the voltage output of Inventer.

Actually you can imagine it. Which electronic components need positive and negative poles, resistance, and inductance are generally not needed. Diodes are generally bad and may be broken down. As long as the voltage is normal, there is generally no problem, and the transistor will not conduct. The voltage regulator tube will be damaged if the positive and negative connections are reversed, but generally some circuits are protected by unidirectional conduction of diodes. Now it is a capacitor. The positive and negative parts of the capacitor are electrolytic capacitors. If the positive and negative connections are severely reversed, the shell will burst.

The main component diode. Switch tube oscillating transformer. sampling. Widen the tube. There is also the circuit principle of the resistance and capacitance isotonic switching circuit of the oscillation circuit.

The choice of the main power components of the inverter is very important. Currently, the most used power components are Darlington Power Transistor (BJT), Power Field Effect Transistor (MOSFET), Insulated Gate Transistor (IGBT) and Shutoff Thyristor ( GTO), etc., MOSFETs are used more in small-capacity and low-voltage systems, because MOSFETs have lower on-state voltage drops and higher switching frequencies. IGBT modules are generally used in high-voltage and large-capacity systems. This is because The on-state resistance of MOSFET increases as the voltage increases, while IGBT has a greater advantage in medium-capacity systems, while in super-large-capacity (above 100KVA) systems, GTO is generally used as a power element.

Large parts: FETs or IGBTs, transformers, capacitors, diodes, comparators, and main controllers such as 3525. AC-DC-AC inverter also has rectification and filtering.

The power size and accuracy are related to the complexity of the circuit.

IGBT (Insulated Gate Bipolar Transistor) is a new type of power semiconductor field-controlled self-shutdown device, which combines the high-speed performance of power MOSFET with the low resistance of bipolar devices. It has high input impedance, low voltage control power consumption, and simple control circuit. , High voltage resistance, high current capacity and other characteristics, it has been widely used in various power conversion. At the same time, major semiconductor manufacturers continue to develop high withstand voltage, high current, high speed, low saturation voltage drop, high reliability, and low cost technologies for IGBTs, mainly using manufacturing processes below 1um, and some new progress has been made in research and development.

1. Working principle of full control inverter

For the commonly used single-phase output full-bridge inverter main circuit, the AC components use IGBT tubes Q11, Q12, Q13, and Q14. And by PWM pulse width modulation control IGBT tube on or off.

When the inverter circuit is connected to the DC power supply, Q11 and Q14 are turned on first, and Q1 and Q13 are turned off, the current is output from the positive pole of the DC power supply, through Q11, L or the inductor, the primary coil of the transformer Figure 1-2, to Q14 To the negative pole of the power supply. When Q11 and Q14 are cut off, Q12 and Q13 are turned on, and the current flows from the positive pole of the power supply through Q13, the transformer primary winding 2-1 inductance to Q12 and returns to the negative pole of the power supply. At this time, on the primary coil of the transformer, a positive and negative alternating square wave has been formed. Using high-frequency PWM control, two pairs of IGBT tubes are alternately repeated to generate an alternating voltage on the transformer. Due to the role of the LC AC filter, a sine wave AC voltage is formed at the output.

When Q11 and Q14 are turned off, in order to release the stored energy, diodes D11 and D12 are connected in parallel at the IGBT to return the energy to the DC power supply.

2. Working principle of semi-controlled inverter

The semi-controlled inverter uses thyristor components. Th1 and Th2 are thyristors that work alternately. If Th1 is first triggered and turned on, the current flows through Th1 through the transformer. At the same time, due to the induction of the transformer, the commutation capacitor C is charged to twice the power supply voltage. Pressing Th2 is triggered to turn on, because the anode of Th2 is reversely biased, Th1 is turned off and returns to the blocking state. In this way, Th1 and Th2 commutate, and then the capacitor C is charged in reverse polarity. In this way, the thyristor is triggered alternately, and the current alternately flows to the primary of the transformer, and alternating current is obtained at the secondary of the transformer.

In the circuit, the inductance L can limit the discharge current of the commutation capacitor C, extend the discharge time, and ensure that the circuit turn-off time is greater than the turn-off time of the thyristor, without the need for a large-capacity capacitor. D1 and D2 are two feedback diodes, which can release the energy in the inductance L and send the remaining energy in the commutation back to the power supply to complete the energy feedback function.
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