What is a Gate Emitter Threshold Voltage of an IGBT?

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Editorial Team - everything PE

Jul 19, 2023

Gate-Emitter Threshold Voltage, VGE(th) refers to the voltage required at the gate terminal of an IGBT to turn it on and establish a conducting channel between the collector and emitter terminals. In other words, it is the minimum voltage level that needs to be applied to the gate-emitter junction to enable the IGBT to start conducting current.

Transfer Characteristics of an IGBT

Importance of Gate Emitter Threshold Voltage

  • Turn-On and Turn-Off Behavior: The gate-emitter threshold voltage influences the turn-on and turn-off characteristics of an IGBT. When the gate voltage exceeds VGE(th), the IGBT starts conducting current, and the device is in the "on" state. Conversely, when the gate voltage drops below VGE(th), the IGBT turns off, entering the "off" state. Proper control of VGE(th) is crucial for achieving efficient switching performance.
  • Gate Drive Circuit Design: The VGE(th) specification is a critical parameter to consider when designing the gate drive circuitry for an IGBT. The control circuit must supply a gate voltage that exceeds VGE(th) to ensure a reliable turn-on and provide a safety margin to compensate for variations in manufacturing parameters and operating conditions.
  • Static and Dynamic Characteristics: VGE(th) affects the static and dynamic characteristics of an IGBT. The static characteristics include parameters such as on-state voltage drop and leakage current, while the dynamic characteristics encompass switching speed, conduction losses, and turn-off delays. Optimizing VGE(th) helps in achieving a balance between these characteristics, ensuring efficient and reliable IGBT operation.

Factors Affecting Gate Emitter Threshold Voltage

Several factors influence the value of VGE(th) in an IGBT. Understanding these factors is vital for effective circuit design and performance analysis. The key factors affecting VGE(th) are:

  • Temperature: VGE(th) exhibits a temperature dependency, meaning it changes with variations in ambient temperature. Typically, VGE(th) increases with temperature. This characteristic should be considered when designing IGBT-based systems that operate in wide temperature ranges.
  • Process Variations: The manufacturing process and variations in material properties can cause slight deviations in VGE(th) values among different IGBTs. Designers must consider these process variations and ensure appropriate gate drive voltages for reliable operation across different devices.
  • Aging and Wear: Over time, IGBTs may experience aging effects that can affect their electrical characteristics, including VGE(th). Long-term usage, voltage spikes, and operating conditions outside the specified limits can contribute to wear and changes in VGE(th). Periodic testing and monitoring can help identify any shifts in VGE(th) due to aging.

To ensure proper control and operation of IGBTs, it is crucial to accurately measure and control VGE(th). The following methods are commonly employed:

  • Threshold Voltage Measurement: Various test setups and equipment, such as source-measure units (SMUs) or curve tracers, can measure VGE(th) by applying different gate-emitter voltages and observing the corresponding IGBT current response.
  • Gate Drive Circuit Design: Designing an appropriate gate drive circuit is essential to supply the required voltage level exceeding VGE(th).

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