Curious Case of EC mosfet body diode

122

01:21:24

Real world MOSFETs have something called a body diode. In EC, the MOSFETs seem to have a body diode, but with strange characteristics. The body diode works when the gate and source are shorted, doesn't work when the gate is left open and becomes non-existent when the gate and drain are shorted. Also, the cut-in voltage of the EC body diode is equal to the gate-source threshold voltage!!

published 6 years ago

kiani

6 years ago

Wish EC would come out of cupboard, and tell us bout their components,,, i wonder what the @EC.info would say about the MISSING manual of use.. Lol.

rich11292000

6 years ago

If gate voltage is higher than source or drain then the fet will start conducting. The simulation is identical if drain and source are reversed.

PrathikP

6 years ago

What are you talking about? I'm not worried about the fet part of the fet. I'm interested in figuring out what the deal is with the diode part of the fet in ec

rich11292000

6 years ago

There isn't a body diode. The model doesn't care how its orientated.

PrathikP

6 years ago

Not entirely correct. When G and S terminals are shorted, the D and S path clearly exhibits diode characteristics (left most circuit), but in the other cases it doesn't, Which is weird.

rich11292000

6 years ago

http://everycircuit.com/circuit/5649392036741120

rich11292000

6 years ago

Even this guy knows http://everycircuit.com/circuit/6707341849001984

PrathikP

6 years ago

The statement "there is no distinction between drain and source in EC" is incorrect. MOSFETs are bidirectional in real life too. Their conductive path is just an N channel or P channel, with is a resistive path, and does not contain any bipolar junctions.

PrathikP

6 years ago

And i have clearly mentioned in my circuit discription that a shottkey is placed parallel to the mosfet to reduce power losses, and not because there isn't a body diode. Read carefully

PrathikP

6 years ago

The fact that mosfets are bidirectional is exactly why a synchronous buck Converter is possible. The lower MOSFET conducts current from source to drain when it is on

PrathikP

6 years ago

You are typically used to designing your circuit in such a way that current flows from drain to source, like in the case of a simple LED PWM dimmer, because on swapping D and S, current continuously flows through the body diode and PWM becomes ineffective

PrathikP

6 years ago

But in case of a sync converter, during the dead time, current flows through the body diode of the lower fet (or a parallel diode, which is used because it offers a lower forward voltage drop) and when the lower fet is turned of, current flows from the source to drain due to the bidirectional natural of its n channel.

PrathikP

6 years ago

You can try this out in real life too. Also, mosfet solid state relays are possible only because of the bidirectional nature of mosfet channel

PrathikP

6 years ago

http://everycircuit.com/circuit/5169011642597376

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