VI Characteristics of IGBT Explained

VI characteristics of IGBT is the graphical relationship between collector current and collector-emitter voltage (V_CE) for different values of gate-emitter voltages. It is basically a plot of collector current (I_C) versus collector-emitter voltage for various values of gate-emitter voltage (V_GE).

VI characteristics of IGBT is also known as Static or Output Characteristics. Let us now discuss the required circuit diagram and VI characteristics.

The circuit diagram for obtaining VI characteristics of IGBT is shown below. This circuit comprises of voltage source V_CC to make the IGBT (Insulated Gate Bipolar Transistor) collector-emitter forward biased, resistor R_s in series with the gate circuit and resistance R_GE connected in shunt with gate-emitter.

The gate-emitter voltage (V_GE) is varied and the collector-emitter voltage (V_CE) and collector current (I_C) is measured. Then a plot between I_C & V_CE is drawn. This plot is the required static characteristics of IGBT.

The VI characteristics of IGBT is shown below:

Following points may be noted from the above VI characteristics of IGBT:

• When the device is forward biased, the shape of output characteristics is similar to that of BJT. However, the controlling parameter in case of IGBT is V_GE as it is a voltage-controlled device.
• When the device is reversed biased, there is a voltage beyond which breakdown occurs. This reverse voltage is shown to be V_RM.
• There is a maximum voltage in forward conduction mode beyond which collector-emitter breakdown occurs and gate losses control of collector current.

There is one more static characteristic of IGBT which is called the transfer characteristics. Let us now discuss this in brief.

Transfer Characteristics of IGBT:

The transfer characteristics of IGBT is basically a plot of collector current I_C versus gate-emitter voltage (V_GE). The transfer characteristics is shown below.

It may be noted from the above curve that when gate-emitter voltage is less than a minimum voltage (V_GET), no current flows through the IGBT. This means , a minimum amount of forward voltage is required to make IGBT turn ON.