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IGBT: Gate Emitter Voltage Clarification from datasheet

IGBT: Gate Emitter Voltage Clarification from datasheet

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Gate voltage levels for IGBT


In switching devices like IGBT the gate-emitter voltages play a critical role in turning ON and turning OFF the device determining the amount of current flow through the collector to the emitter. These gate voltages are classified as follows:

  1. Threshold voltage level
  2. Steady-state voltage level (Recommended operating voltage level)
  3. Transient voltage level
Threshold voltage level


If the gate-emitter voltage is less than the threshold voltage level than the minimum threshold voltage, the device does not conduct. A minimum threshold voltage as mentioned in the datasheet has to be applied for the device to conduct.

Steady-state voltage level (Recommended operating voltage level)


The voltage required for the device to conduct in steady state and to withstand continuous voltage without damaging itself. It is always recommended to operate the device in steady state voltage level for better performance and lifetime.

Transient voltage level


The maximum voltage that the device can withstand without damaging itself for a short duration of time (typically values will be mentioned in the datasheet).

During switch ON, transient gate-emitter voltage changes from negative or zero to positive voltage level (above threshold voltage level). During switch OFF transient gate-emitter voltages changes from positive voltage level to zero or negative voltage level.
Figure 1 shows the different gate voltages.

KA-15117_Image1.pngFigure 1. Gate voltages


How much time does the device withstand in transient condition?


In transient condition, the voltage swing appears in both positive side and negative side. Voltage level and time both are mentioned in the test condition as shown in Figure 2.

KA-15117_Image2.png

 

Figure 2. Time and voltage level


In Figure 2, the first voltage level is the steady state voltage level and the second one is the transient voltage level. This means in steady state the device can withstand upto 20 V and accept the swing of 10 V in both positive and negative directions.

This transient voltage level of 30 V can withstand a pulse time of 10 us and duty of less than 0.010. This means even though the switching frequency is changing the time and duty have to remain constant (ideally duty should be less than 1%), and only the device can safely withstand the transient voltage level.

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