The body diode is an important component of a MOSFET, which is the PN junction between the substrate (B) and the drain (D). Since the B and S terminals are shorted, the body diode between SD appears. Today, we will briefly discuss the role of the body diode in a MOSFET and how much current it can handle.

What is the body diode?

A MOSFET has two PN junctions: the source-substrate (SB) and the drain-substrate (DB). Because the source (S) and the substrate (B) are shorted, only the PN junction between the drain (D) and the source (S) remains, which is the body diode, also known as the parasitic diode. The conduction current of the body diode depends on the process and structure of the MOSFET.

What is the role of the body diode?

One important role of the body diode of a MOSFET is to protect against overvoltage on VDD (power supply voltage). When the power supply voltage exceeds the rated voltage of the MOSFET, the diode will first break down in reverse bias, directing a large current directly to the ground, thereby preventing the MOSFET from being damaged due to overvoltage. This protection is crucial for the MOSFET as it can effectively improve its lifespan and reliability.

How much current can the body diode of a MOSFET handle?

This mainly depends on the specifications and design of the MOSFET. Generally, the maximum current of the body diode of a MOSFET will not exceed the maximum current between the drain and the source. The body diodes of enhancement-mode nMOSFETs and pMOSFETs can handle relatively large currents, typically ranging from a few milliamperes to several amperes.

It is important to note that although the body diode can handle a certain range of current, it is generally not recommended to operate it close to the limit value of reverse breakdown current to ensure the stability and reliability of the MOSFET. Additionally, when designing circuits, the current carrying capacity of the MOSFET's body diode should be fully considered to avoid MOSFET damage due to excessive current.