Puporse of schottky diode in a MOSFET - Electronic Circuits Projects Diagrams Free

sazerac99us · 31st August 2006, 07:03 PM

While trying to select a MOSFET for a project, I see a lot of them incorporate a schottky diode. What is the purpose of this?

Analog · 31st August 2006, 07:38 PM

Quote:

Originally Posted by sazerac99us

While trying to select a MOSFET for a project, I see a lot of them incorporate a schottky diode. What is the purpose of this?

Look at Figure 7, and the paragraph before it:

http://www.irf.com/technical-info/appnotes/an-967.pdf

sazerac99us · 2nd September 2006, 02:05 PM

How would this affect using one of these in a simple switching application a reverse polarity protection circuit?

dknguyen · 2nd September 2006, 10:43 PM

Wouldn't you just use a diode in a reverse polarity protection circuit?

Are you sure you aren't referring to the parasitic diode that's always present in a MOSFET? Or are you actually referring to a diode they integrated into the MOSFET on purpose?

Your last sentence didn't seem to make too much sense though. Try writing two sentences.

sazerac99us · 3rd September 2006, 07:06 AM

Yeah...I was cutting and pasting and it didnt work out. A lot of the data sheets that I've seen of MOSFETs have a diode or schottky diode in the symbol . Im planning on using a mosfets as a simple 12V switch, and also as reverse polarity protection (a regular diode will drop about .7 V, but with a mosfet, there would be less. (see figure D)

http://www.elecdesign.com/Files/29/9945/Figure_01.gif

Sorry about the poor previous post.

dknguyen · 3rd September 2006, 07:30 AM

THose are the intrinsic parasitic diodes that come with every MOSFET. They don't purposely put it in. It just ends up there always. There is no real reason people "put it in". It's supposed to be a very powerful, but very slow diode. I guess for some reason they have less voltage drop than REGULAR diodes so you can use this to your advantange. I'm pretty sure if you don't look for regular diodes you will find diodes with less voltage drop than the MOSFET intrinsic diode. It's not hard to find MOSFET intrinsic diodes with much higher voltage drops than discrete diodes- just hunt around on IRF's datasheets for a while.

eblc1388 · 3rd September 2006, 07:51 AM

Quote:

Originally Posted by sazerac99us

Yeah...I was cutting and pasting and it didnt work out. A lot of the data sheets that I've seen of MOSFETs have a diode or schottky diode in the symbol . Im planning on using a mosfets as a simple 12V switch, and also as reverse polarity protection (a regular diode will drop about .7 V, but with a mosfet, there would be less. (see figure D)

http://www.elecdesign.com/Files/29/9945/Figure_01.gif

Sorry about the poor previous post.

The secret in polarity protection circuit using MOSFET is to exchange the original purpose of DRAIN and SOURCE pin so that the polarity of the instrinsic diode is now the right way round.

Hero999 · 3rd September 2006, 10:13 AM

I've tried that and it works very well too. With other control circuitry MOSFETs make very good bridge rectifiers as well.

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31st August 2006, 07:03 PM	(permalink)
sazerac99us	Puporse of schottky diode in a MOSFET While trying to select a MOSFET for a project, I see a lot of them incorporate a schottky diode. What is the purpose of this?

2nd September 2006, 02:05 PM	(permalink)
sazerac99us	How would this affect using one of these in a simple switching application a reverse polarity protection circuit?

2nd September 2006, 10:43 PM	(permalink)
dknguyen	Wouldn't you just use a diode in a reverse polarity protection circuit? Are you sure you aren't referring to the parasitic diode that's always present in a MOSFET? Or are you actually referring to a diode they integrated into the MOSFET on purpose? Your last sentence didn't seem to make too much sense though. Try writing two sentences.

3rd September 2006, 07:06 AM	(permalink)
sazerac99us	Yeah...I was cutting and pasting and it didnt work out. A lot of the data sheets that I've seen of MOSFETs have a diode or schottky diode in the symbol . Im planning on using a mosfets as a simple 12V switch, and also as reverse polarity protection (a regular diode will drop about .7 V, but with a mosfet, there would be less. (see figure D) http://www.elecdesign.com/Files/29/9945/Figure_01.gif Sorry about the poor previous post.

3rd September 2006, 07:30 AM	(permalink)
dknguyen	THose are the intrinsic parasitic diodes that come with every MOSFET. They don't purposely put it in. It just ends up there always. There is no real reason people "put it in". It's supposed to be a very powerful, but very slow diode. I guess for some reason they have less voltage drop than REGULAR diodes so you can use this to your advantange. I'm pretty sure if you don't look for regular diodes you will find diodes with less voltage drop than the MOSFET intrinsic diode. It's not hard to find MOSFET intrinsic diodes with much higher voltage drops than discrete diodes- just hunt around on IRF's datasheets for a while. Last edited by dknguyen; 3rd September 2006 at 07:36 AM.

3rd September 2006, 10:13 AM	(permalink)
Hero999	I've tried that and it works very well too. With other control circuitry MOSFETs make very good bridge rectifiers as well. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.