Shottky versus rectifier diode 1

[eeprom]

In parts catalogs, the diodes are often divided as shottky and rectifier. I realize that there are performance differences (speed), but are these two items really different? Can someone explain the difference between a shottky diode and a rectifier diode?

thanks
EE

 

[Noway2]

The biggest difference that I know of is that a schottky diode uses a different process to create the PN junction. This causes the forward voltage drop to be lower, at about 0.3V as opposed to the standard (rectifier) drop of about 0.7V. Of course, this will have an effect on other operational parameters, as you pointed out.

 

[zappedagain]

Voltage drop is my first thought too when I think of a Schottky. They come in very handy for polarity protection on power supplies. Especially if you get one that can handle much more current than your typical, and then the voltage drop is even lower than 0.3V.

John D

 

[IRstuff]

A Schottky diode has metal as on of the two sides of the junction, unlike regular semiconductor diodes, which have semiconductor on both sides. The work function for metal is drastically different than for silicon, resulting in a diode whose forward drop is considerably lower than a semiconductor diode.

Because there is only one semiconductor side, which is usually heavily doped, a Schottky diode will have a drastically shorter recovery time, since there is little or no charge storage in the junction.

However, Schottkys, if I recall correctly generally have lower reverse breakdown voltages.

TTFN

FAQ731-376

 

[eeprom]

So, they both perform the same function. But the shottky has some performance improvements, especially with respect to forward voltage drop. I didn't know that about the forward voltage drop. That is good information. Thanks for the help.

 

[IRstuff]

Schottky diodes were in their heyday when Schottky TTL logic devices were the fastest you could get without going to ECL or GaAs. They were used to strap the base-collector junctions on critical transistors to keep them out of saturation by bypassing B-C junction with the Schottky diode, which had effectively no storage recovery time.

TTFN

FAQ731-376

 

[itsmoked]

Of course there had to be a reason all diodes aren't automatically Schottkys. The big down side of Schottkys is they have lousy really lousy leakage. So, if you back bias them they will leak much more than any Si diode.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[zappedagain]

That's a star for you! I was waiting for someone to post a drawback to the holy grail of diodes.

 

[itsmoked]

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electricuwe]

To IRStuff:
'However, Schottkys, if I recall correctly generally have lower reverse breakdown voltages'

That is true for Schottky-Diodes based on Silicon, but today Schottky-diodes made from Siliconcarbide (SiC) are readily available and already find significant use in PFC-circuits.

To all:
If considering the use of these devices for rectification you should consider that current state of the art for efficient rectification (voltages up to 48 V) is sychronous rectification using Mosfets.

 

[sreid]

"Rectifier" diodes are specifically designed for the rectification of low frequency AC Power. The important feature about them is how rugged they are. For example, they are rated for single cycle surge current.

 

[StephenVB]

The response time of a diodes can be critical. I once accidently (it was in the wrong drawer) used a 1N4004 in a switching power supply and it's response was so slow that it might as well have been a wire. The data sheet I have on a 1N400* says nothing about response time but it's slow, OK for AC rectification and so on.

I have been using Schottky diodes for circuit protection, for example tied from analog inputs to 5 volts to prevent transients and over voltage from blowing the ADC. I used them because of their response time.

I had no idea how bad their reverse leakage was. I guess I need more practice at reading data sheets. A 1N5819 has 10mA reverse leakage at 100 degrees C at 40V reverse voltage - I have no idea how it is at lower voltages, where I use them. A 1N4001 has 4 microA (how do you enter special characters?). The Schottky reverse leakage hasn't been a problem so far as I've noticed, but boy howdy, it certainly could be.

 

[IRstuff]

It's amazing what you can find on the internet, sometimes:

http://www.avtechpulse.com/appnote/techbrief9/

The second waveform picture shows a 1N4004 recovering, with a measured t.rr = 1.2 us

TTFN

FAQ731-376

 

[itsmoked]

I think generally 1kHz is It for 1N400x apps.

We used to use 1N6263s for A2D front end protection. High temperature would wreak havoc. High temps like a measly 45C.
They leak like a sieve when they get warm.



Keith Cress
kcress -

http://www.flaminsystems.com