Why diode is connected across IGBT and MOSFET? Body or Intrinsic Diode

Today we are going to know why diodes are connected in antiparallel with IGBT and MOSFET, what is the body diode or intrinsic diode in a power MOSFET. Generally, low power MOSFETs have not any Body Diode or Intrinsic Diode but the high power rated power MOSFETs have. The body diode is also called parasitic diode or internal diode. We need to connect an external diode in antiparallel with the low power MOSFETs for certain applications.

Why we need to connect external diodes in antiparallel across IGBT and MOSFET?

We need to connect the external diode to provide a path for reverse current. We know that MOSFET or IGBT is a unidirectional device, they only conduct current in forward bias and block the current in reverse bias.

So when an inductive load is connected with MOSFET a reverse voltage appears across the MOSFET which produced by the inductive load. This reverse voltage may damage the MOSFET. For this reason, an external diode is connected across the MOSFET or IGBT or SCR to provide a path for reverse current.

Sometimes an external diode is connected across the MOSFET(low power rated) in parallel as a body diode for high-speed switching applications because the internal diode cannot work properly in high-speed switching or H-Bridge applications.

What is Body Diode in MOSFET?

As I told before low power MOSFETs does not have any Body diode but high power diodes have body diode. Generally, the body diode is connected between drain and source. The body diode in a MOSFET is nothing but a normal PN Junction Diode. The voltage and current rating of the body diode are the same as the rating of MOSFET itself.

The structure of the body diode is inherent in the construction of the MOSFET and it points to the body of the MOSFET, that is why it is also called an Intrinsic Diode.


The body diode in a MOSFET used for the following reasons.

1. The body diode provides a path for reverse drain current or freewheeling purpose when the MOSFET is connected with inductive load.

2. The body diode in a MOSFET acts as a camper and maintain the gate voltage with respect to the source and drain under an appropriate level.

3. The body also provides very reverse recovery time for high-speed switching applications.

Read Also:

• Actual Difference Between Oscillator and Amplifier
• Main Difference Between PN Junction Diode and Zener Diode
• How and Why Zener Diode Regulate Voltage in Reverse Bias?
• Why all Electronic Devices Works on DC not AC?

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