Mosfet as a Diode

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  • Last Post 10 September 2018
Marathonman posted this 08 September 2018

I really did not want to open up another thread as most of my time is spent on the Figuera device but i just wanted to share this that may help other and possibly be used in their circuits.

Below is a group of Mosfets that are used as a Diode with no voltage drop or losses what so ever like that of a diode. if logic level transistor are used the transistor will turn on at a very low voltage level thus when fully on will not have any such voltage drop. by connecting the gate and a resistor to the high side each pair of Mosfets will turn on and off with respects to being positive or negative. this can replace diodes as well as a commutator in systems like the Figuera device feed back to the system.

Please,  all feedback is welcomed whether it be thumbs up or thumbs down or ways to improve.

Regards,

Marathonman

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Vidura posted this 08 September 2018

The mosfet can certainly used as rectifier, but it works backwards in this mode, conducing in Source-Drain direction(the colors of the gatedrives are inverted), and there is the problematic of the hiside switch when n channel mosfets are used. To make conductive the hiside switch you need at least 10 volts over the railvoltage.For lowside switching it is commonly used as synchronous rectifier, and can be directly driven by a inverter circuit for example. Regards Vidura.

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Marathonman posted this 08 September 2018

I thank you for the advice but i am sure you know current runs from negative to positive not the other way around. as for the rest, i do understand.

Regards Marathonman

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Chris posted this 08 September 2018

A useful thread, thanks MM.

Some time ago I read a paper about M.E.R.S - Magnetic Energy Recovery System.

I believe I have posted here and also to other threads else where. M.E.R.S uses Mosfets in an H-Bridge arrangement to switch and recover Reactive Return Power and does it very efficently.

Graham Gunderson has also presented a concept well known called Synchronous Rectification. Using Mosfets as Diodes. Switching them at a specific Timing.

Both names have changed, but you get the idea.

I believe it is very important to note, a Mosfet is a two way device, Current can pass both ways if the Mosfet is on. I did post some data about this here: What LED's will Light?

 

Thats right, there is a parasitic Diode in all Mosfets as far as I know, its called the body diode.

I hope this is useful for others!

   Chris

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Marathonman posted this 08 September 2018

"I believe it is very important to note, a Mosfet is a two way device, Current can pass both ways if the Mosfet is on."

Exactly,  a thing most people do not know.

Regards,

marathonman

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Marathonman posted this 09 September 2018

So high side PNP's should be used  for the most simple circuit as NPN would require a bootstrap cap and other circuitry.

you have to admit  in a power sensitive circuit where every joule counts this would be worth the effort pursuing.

 

Regards,

Marathonman

Chris posted this 10 September 2018

Hey MM,

Of course application is the engineers decision.

   Chris

 

Marathonman posted this 10 September 2018

OF course, and i think the use of enhanced transistor would make it an easier road to travel.

Regards,

Marathonman

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