Dynamic characteristics and turn-on process of IGBT
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Dynamic characteristics and turn-on process of IGBT

Posted Date: 2024-02-08

Dynamic characteristics of IGBT

The dynamic characteristics of an IGBT (Insulated Gate Bipolar Transistor) include characteristics in the on-state and off-state. The following are its main dynamic characteristics:

1. On state:

- Saturation voltage drop speed (VCE (sat) drop speed): During turn-on, when the gate voltage is higher than the threshold voltage, current starts to pass through the IGBT. The saturation voltage drop rate indicates how quickly VCE (collector-emitter voltage) drops when IC (collector current) rises to a specific value.

- Turn-on speed: refers to the conversion speed of IGBT from off state to on state. Faster turn-on speed helps reduce switching losses.

- Saturation voltage (VCE(sat)): guides the collector-emitter voltage during the pass-through process. Lower saturation voltage reduces power consumption.

- Forward current conduction loss: refers to the power loss when the IGBT is turned on, which is related to the turn-on voltage and current.

2. Off state:

- Turn-off speed: refers to the switching speed of IGBT from on state to off state. Faster turn-off speed helps reduce switching losses.

- Turn-off characteristics: including turn-off current, turn-off voltage, turn-off time, etc. The turn-off voltage refers to the collector-emitter voltage during the IGBT turn-off process, and the turn-off time refers to the time required for the IGBT to go from conduction to complete turn-off.

- Anti-parallel diode performance: The IGBT integrates an anti-parallel diode, and its conduction and turn-off characteristics are also important to the performance of the entire device.

These dynamic characteristics are very important for IGBT performance and applications. High conduction efficiency, low switching losses and fast switching speed are some of the key requirements, especially in high frequency and high power applications. Therefore, the dynamic characteristics of IGBTs have been extensively studied and improved to meet various application needs.

IGBT commissioning process

The turn-on process of an IGBT (Insulated Gate Bipolar Transistor) refers to the process from the off state to the on state, which mainly involves the application of the gate signal and the current flow inside the transistor. The following is the general IGBT opening process:

1. Off state: In the off state, no current flows through the IGBT. At this time, the voltage between gate and source is lower than the threshold voltage (Vth), compared with the gate-source voltage (VGS), VGS

2. Rising edge trigger: Apply a positive voltage pulse to the gate of the IGBT. The gate voltage exceeds the threshold voltage such that the gate-source voltage VGS >> Vth. This creates a strong electric field, forming a sloping channel along the oxide layer and N-region under the insulating gate.

3. Initiate conduction: Through the electric field of the gate, the charge is controlled to form a conductive channel on the surface of the N region. This channel will connect the N+ and P regions, allowing current to flow from the collector and to the emitter.

4. Thermal diffusion: Once the conductive channel is formed, current starts passing through the IGBT. Due to the forward current in the structure, current diffusion begins to occur on the surface around the P region, and the diffusion area will further expand.

5. Saturation state: When the current increases to a certain level, the IGBT enters the saturation state. In saturation, the drop between voltages is very small and the collector-emitter voltage (VCE) is close to the saturation voltage (VCE(sat)).

Through these steps, the IGBT successfully transitions from the off state to the on state. The turn-on process of IGBT is mainly controlled by the control of the gate signal and the internal current flow path. This turn-on process requires accurate application of the gate signal and proper circuit design to achieve accurate switching operation.

Review Editor: Huang Fei


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