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How can you protect IGBTs from overvoltage?

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Overvoltage is one of the most common causes of failure for insulated gate bipolar transistors (IGBTs), which are widely used in power electronics applications such as inverters, converters, and drives. Overvoltage can damage the gate oxide layer, create parasitic currents, and trigger thermal runaway. To protect IGBTs from overvoltage, you need to understand the sources, effects, and solutions of this phenomenon. In this article, you will learn how to prevent and mitigate overvoltage in IGBTs using different methods and techniques.

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Yi Zhang

Assistant Professor at Aalborg University, Denmark
Nima Zamro

Power Electrical Engineer at MAPNA Boiler and Equipment Engineering and Manufacturing Co.
Cuong Tran Duc

Business Partner @ CM Group | LinkedIn - ?? Top Renewable Energy Voice | Vietnam - ?? Top 10 LinkedIn Voices | ??…

1 Sources of overvoltage

Overvoltage can occur due to various factors, such as switching transients, load changes, line disturbances, and external faults. Switching transients are generated by the rapid change of voltage and current during the turn-on and turn-off of IGBTs, which can induce voltage spikes across the device and the circuit. Load changes can cause overvoltage when the output voltage of an inverter or converter exceeds the input voltage due to the change of power factor or load impedance. Line disturbances can result from grid faults, lightning strikes, or switching of other devices on the same network, which can create voltage surges or sags. External faults can happen when a short circuit or an open circuit occurs in the load or the power supply, which can cause overcurrent or overvoltage in the IGBTs.

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Yi Zhang

Assistant Professor at Aalborg University, Denmark
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Switching transient caused over voltage is highly related the parasitic inductance of the printed circuit board. Moreover, over voltage is often occurring when multiple IGBTs are connected in series. The little difference of gate circuits or the device themselves will cause the unbalanced voltage across different IGBTs

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Nima Zamro

Power Electrical Engineer at MAPNA Boiler and Equipment Engineering and Manufacturing Co.
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To protect Insulated Gate Bipolar Transistors (IGBTs) from overvoltage, you can employ the following methods: 1. Snubber Circuits 2. Clamping Circuits 3. Overvoltage Protection Devices 4. Gate Resistors 5. Gate-Drive Transformers 6. Proper Layout and Grounding 7. Voltage Clamps 8. Feedback Control Remember, the specific protection method may vary based on the application and the IGBT’s characteristics, so it’s essential to consult the manufacturer’s guidelines and specifications for optimal protection.

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2 Effects of overvoltage

Overvoltage can have detrimental effects on the performance and reliability of IGBTs. The most critical effect is the breakdown of the gate oxide layer, which is a thin film of silicon dioxide that isolates the gate from the channel. The gate oxide layer has a limited withstand voltage, and if it is exceeded, it can create holes or cracks that allow current to flow between the gate and the channel. This can cause permanent damage to the IGBT, reduce its gain, increase its leakage, and degrade its switching speed. Another effect of overvoltage is the generation of parasitic currents, which are unwanted currents that flow through the parasitic capacitances and inductances of the device and the circuit. These currents can cause additional power losses, heating, and electromagnetic interference. A third effect of overvoltage is the initiation of thermal runaway, which is a positive feedback loop that increases the temperature and the current of the IGBT until it reaches its thermal limit and fails.

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3 Solutions for overvoltage

In order to protect IGBTs from overvoltage, you must apply solutions that can either prevent or reduce its occurrence and impact. Snubber circuits, for example, are passive circuits made up of resistors, capacitors, and diodes connected in parallel or series with the IGBTs. They are designed to absorb energy from switching transients and limit the rate of voltage and current change, reducing voltage spikes and extending the lifetime of IGBTs. Clamping circuits are active circuits that use transistors, diodes, and zener diodes to clamp the voltage across IGBTs to a safe level. Additionally, overvoltage protection devices such as relays, fuses, circuit breakers, and surge arresters can be integrated or connected to the IGBTs to detect and respond to overvoltage conditions. Knowing the sources, effects, and solutions of overvoltage is essential for selecting the best method and technique to protect IGBTs from overvoltage in power electronics applications.

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Cuong Tran Duc

Business Partner @ CM Group | LinkedIn - ?? Top Renewable Energy Voice | Vietnam - ?? Top 10 LinkedIn Voices | ?? Advisor in Energy Development Strategy??
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Active clamp technology: This method uses a clamp circuit to limit the voltage across the IGBT during turn-off, especially under short-circuit conditions. The clamp circuit consists of a capacitor, a diode, and a switch, which are connected in parallel with the IGBT. The capacitor absorbs the energy stored in the stray inductance of the circuit, and the switch controls the discharge of the capacitor. This method can reduce the protection time of IGBT at overvoltage to hundreds of nanoseconds.

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4 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Cuong Tran Duc

Business Partner @ CM Group | LinkedIn - ?? Top Renewable Energy Voice | Vietnam - ?? Top 10 LinkedIn Voices | ?? Advisor in Energy Development Strategy??
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Some more of the common methods are: 1| Gate driver circuit. This method uses a gate driver circuit to monitor the current and voltage of the IGBT, and to turn off the gate signal when a fault is detected. The gate driver circuit can also provide isolation, level shifting, and protection features for the IGBT. 2| Snubber circuit. This method uses a snubber circuit to suppress the voltage spikes and ringing that occur during the switching of the IGBT. The snubber circuit consists of a resistor and a capacitor, which are connected in series with the IGBT. The resistor limits the rate of rise of the current, and the capacitor limits the rate of fall of the voltage.

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1 Sources of overvoltage

2 Effects of overvoltage

3 Solutions for overvoltage

4 Here’s what else to consider

Power Engineering

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How can you protect IGBTs from overvoltage?

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1 Sources of overvoltage

2 Effects of overvoltage

3 Solutions for overvoltage

4 Here’s what else to consider

Power Engineering

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