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The title says it all: What does this Mosfet Symbol mean (two diodes facing each other at Vgs)? I know its an N-MOS, but I don't understand the meaning/purpose of the two diodes.

Part: AO7404

Datasheet Link: http://www.aosmd.com/res/data_sheets/AO7404.pdf

Picture of the symbol (highlighted part):

enter image description here

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2 Answers 2

up vote 10 down vote accepted

It is an ESD clamp, showing that the gate is ESD protected. Typically the back to back diodes are shown as Zeners. This scheme protects against positive and negative ESD hits.

  • In the event of a positive ESD event, the top diode is forward biased, and the bottom diode's reverse breakdown voltage will be exceeded. The ESD is shunted to the source, which is often ground.

  • In the event of a negative ESD event, the top diode's reverse breakdown voltage is exceeded, and the bottom diode is forward biased. The ESD is again shunted to the source.

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Looks little confusing . After looking that the datasheet is from a Chinese supplier one can guess it. edit: That the zener symbol is not correct. enter image description here

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1  
That doesn't really answer the question. –  Matt Young May 17 at 16:35
    
I thought it migth be clear now as you have already explained it nicely... –  Adi May 17 at 16:36
    
@Adi it's a valid contribution –  placeholder May 17 at 16:53
    
Thanks dear placeholder , In the past few years I have dealt with lots of chinese suppliers and they do lots of mistakes in making specs. –  Adi May 17 at 17:06

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