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Q&A Why there is a body diode in mosfets?

in my engineering curriculum .. I never found a diode in a mosfet symbol Then you should ask for your tuition back, or perhaps the institution should want their diploma back. but in datasheets ther...

posted 4y ago by Olin Lathrop‭  ·  edited 4y ago by Olin Lathrop‭

Answer
#2: Post edited by user avatar Olin Lathrop‭ · 2020-10-11T14:29:34Z (about 4 years ago)
  • <blockquote>in my engineering curriculum .. I never found a diode in a mosfet symbol</blockquote>
  • Then you should ask for your tuition back, or perhaps the institution should want their diploma back.
  • <blockquote>but in datasheets there is a diode called as body</blockquote>
  • Right, because there is. It is possible to make such FETs without body diodes, but it is a much more expensive process.
  • <blockquote>Please explain its significance.</blockquote>
  • Other than poor teaching by the school or poor learning by you, you may be confusing formal schematics with something drawn quickly to make a different point, like an instructor might on a board in front of a class. Unless the body diode is important to the context, it is understandable for hand-drawn schematics to not include all the little details.
  • However, when creating schematic symbols in a CAD package, it makes sense to do it right. You're only creating the symbol once, and will use it many times in the future. The extra complexity of the full symbol doesn't matter since you're just including the existing symbol whole into a schematic.
  • In formal contexts like datasheets, it would be irresponsible to omit the details. For example, here is a snippet from the first MOSFET datasheet I happened to grab. It even included an explanation of the symbol:
  • ![Image](https://electrical.codidact.com/uploads/YpkVcSneiXhWw9i5C7Ts5zDx)
  • <blockquote>in my engineering curriculum .. I never found a diode in a mosfet symbol</blockquote>
  • Then you should ask for your tuition back, or perhaps the institution should want their diploma back.
  • <blockquote>but in datasheets there is a diode called as body</blockquote>
  • Right, because there is. It is possible to make such FETs without body diodes, but it is a much more expensive process.
  • <blockquote>Please explain its significance.</blockquote>
  • Other than poor teaching by the school or poor learning by you, you may be confusing formal schematics with something drawn quickly to make a different point, like an instructor might on a board in front of a class. Unless the body diode is important to the context, it is understandable for hand-drawn schematics to not include such details.
  • However, when creating schematic symbols in a CAD package, it makes sense to do it right. You're only creating the symbol once, and will use it many times in the future. The extra complexity of the full symbol doesn't matter since you're just including the existing symbol whole into a schematic.
  • In formal contexts like datasheets, it would be irresponsible to omit the details. For example, here is a snippet from the first MOSFET datasheet I happened to grab. It even included an explanation of the symbol:
  • ![Image](https://electrical.codidact.com/uploads/YpkVcSneiXhWw9i5C7Ts5zDx)
#1: Initial revision by user avatar Olin Lathrop‭ · 2020-10-11T13:47:34Z (about 4 years ago)
<blockquote>in my engineering curriculum .. I never found a diode in a mosfet symbol</blockquote>

Then you should ask for your tuition back, or perhaps the institution should want their diploma back.

<blockquote>but in datasheets there is a diode called as body</blockquote>

Right, because there is.  It is possible to make such FETs without body diodes, but it is a much more expensive process.

<blockquote>Please explain its significance.</blockquote>

Other than poor teaching by the school or poor learning by you, you may be confusing formal schematics with something drawn quickly to make a different point, like an instructor might on a board in front of a class.  Unless the body diode is important to the context, it is understandable for hand-drawn schematics to not include all the little details.

However, when creating schematic symbols in a CAD package, it makes sense to do it right.  You're only creating the symbol once, and will use it many times in the future.  The extra complexity of the full symbol doesn't matter since you're just including the existing symbol whole into a schematic.

In formal contexts like datasheets, it would be irresponsible to omit the details.  For example, here is a snippet from the first MOSFET datasheet I happened to grab.  It even included an explanation of the symbol:

![Image](https://electrical.codidact.com/uploads/YpkVcSneiXhWw9i5C7Ts5zDx)