IGBT Absorption Circuit

An IGBT absorption circuit is a circuit design that is intended to protect an IGBT from damage due to overvoltage when it turns on or off. In a circuit, an IGBT, or insulated gate bipolar transistor, is a high-power, high-speed switch that is widely used in applications such as inverters, motor drives, and power supplies. However, if the IGBT is not turned on or off properly, it can generate high voltage spikes that can damage the IGBT and other electronic components.

Overvoltage is the most common cause of IGBT damage. This overvoltage can be caused by sudden voltage spikes or by the lack of a damping circuit. If an adequate absorption circuit is not used after an IGBT turns off, it can lead to high flyback voltage and damage the IGBT or other electronic devices. Therefore, it is necessary to design an IGBT absorption circuit.

Working principle of IGBT absorption circuit

Before understanding the IGBT absorption circuit, we need to understand the basic concepts of inductance, capacitance, and impedance.

• Inductance (L): Inductance is a measure of the opposition to a change in current. It stores energy in the form of a magnetic field.
• Capacitance (C): Capacitance is a measure of the opposition to a change in voltage. It stores energy in the form of an electric field.
• Impedance (Z): Impedance is the ratio of voltage to current. It is used to measure the relationship between the total current and total voltage in a circuit.

In an IGBT absorption circuit, inductance and capacitance are the main components. The basic principle of this circuit is that when an IGBT turns on, the magnetic field and the charge are stored in the inductance and capacitance. When the IGBT turns off, these stored energies are released and generate high voltage spikes. However, due to the presence of inductance and capacitance, these spikes are smoothed out, reducing the peak voltage.

An IGBT absorption circuit typically includes three main components:

1. Transient voltage suppression diode (TVS diode): TVS diodes are primarily used in reverse voltage applications. When the voltage across the diode exceeds a predetermined value, the diode will breakdown in the reverse direction and conduct a large current to absorb the excess energy.
2. Schottky barrier diode (SBD): SBDs are also fast-responding diodes. They can provide fast switching with very low switching losses, which can help to reduce the voltage spikes during the turn-off process of the IGBT.
3. Inductor (LPF): The inductor is added to the circuit mainly to suppress high-frequency noise, which can reduce the impact of voltage spikes on the IGBT.

Design and optimization of IGBT absorption circuit

Designing a perfect IGBT absorption circuit requires considering multiple factors, including operating frequency, maximum voltage, peak current, and IGBT’s rated current. By optimizing these parameters, high-performance, high-efficiency, and reliable IGBT absorption circuits can be manufactured.

• Operating frequency: When selecting inductors and capacitors, the operating frequency needs to be considered. The selection of the capacitor should ensure that it can store the required voltage at the operating frequency and be able to respond quickly. For the inductor, low-resistance, high-saturation current materials should be used to ensure that it can respond to high-frequency waveforms.
• Maximum voltage: To prevent overvoltage in the circuit, the operating voltage should be less than the peak of its rated voltage. Additionally, when selecting TVS diodes, their reverse breakdown voltage should also be considered.
• Peak current: The peak current is the maximum current that occurs when the IGBT turns on in the circuit. To protect the IGBT from damage, the circuit should be able to withstand these peak currents.
• IGBT’s rated current: When designing the circuit, the IGBT’s rated current should be considered. Exceeding the rated current may damage the IGBT and other electronic components.

Conclusion

An IGBT absorption circuit is an important circuit design that is primarily used to protect an IGBT from damage due to overvoltage. In the circuit, the transient voltage suppression diode, Schottky barrier diode, and inductor are all critical components that help to reduce the voltage spikes and protect the IGBT. Designing and optimizing an IGBT absorption circuit requires considering multiple factors, including operating frequency, maximum voltage, peak current, and IGBT’s rated current.