Schottky

Thread Starter

Chillum

Joined Nov 13, 2014
546
hi, I want to learn more about Schottky diodes (did I get the spelling right? ) I've heard them called barrier diodes. I've also heard about fast recovery and normal Schottky. when does a Schottky become fast recovery and when is it normal? how does their function work (like the lm2576 stepdown psu in "wattage in voltage devider" thread? why a Schottky and not any other diode. what other types of diodes perform what function? lost of questions! :) I'm a student without a school (money) the web is my textbook and allaboutcircuits is my teachers: -)
 

Papabravo

Joined Feb 24, 2006
21,159

crutschow

Joined Mar 14, 2008
34,285
A Schottky diode has a metal-semiconductor junction rather than the semiconductor-semiconductor junction of a normal junction diode. The physics of that means the Schottky diode has no minority carriers and thus no recombination time for the minority carriers to slow down the reverse recovery time. Thus all Schottky diodes are nominally fast recovery. Schottky diodes also have lower forward voltage drop.
It is that fast recovery, plus the lower forward drop, why Schottky diodes are commonly used in high frequency switching power supplies for rectification or free-wheeling diode requirements.

Here's some addition info on them.
 

Thread Starter

Chillum

Joined Nov 13, 2014
546
A Schottky diode has a metal-semiconductor junction rather than the semiconductor-semiconductor junction of a normal junction diode. The physics of that means the Schottky diode has no minority carriers and thus no recombination time for the minority carriers to slow down the reverse recovery time. Thus all Schottky diodes are nominally fast recovery. Schottky diodes also have lower forward voltage drop.
It is that fast recovery, plus the lower forward drop, why Schottky diodes are commonly used in high frequency switching power supplies for rectification or free-wheeling diode requirements.

Here's some addition info on them.

cool! have to read another couple times, but get general idea!
 

crutschow

Joined Mar 14, 2008
34,285
rectification? is that what in switch mode psu? I know how a four diode bridge works.
Isolated switching power supplies with transformers have rectifier diodes at the transformer output to generate DC. Because of the high switching frequency of the transformer driver, the diodes are usually Schottky. They may be configured as a 2 diode full-wave (with center-tapped winding) or 4 diode bridge.

Non-isolated buck or boost regulators don't require rectification but do have free-wheeling (usually Schottky) diodes to carry the inductor current when the switch transistor is in the off part of the cycle.
 

Thread Starter

Chillum

Joined Nov 13, 2014
546
Isolated switching power supplies with transformers have rectifier diodes at the transformer output to generate DC. Because of the high switching frequency of the transformer driver, the diodes are usually Schottky. They may be configured as a 2 diode full-wave (with center-tapped winding) or 4 diode bridge.

Non-isolated buck or boost regulators don't require rectification but do have free-wheeling (usually Schottky) diodes to carry the inductor current when the switch transistor is in the off part of the cycle.
when the switch is in the off part of it's cycle. guess that's why called switching: a diode that's 4ns, is that fast recovery, or are they faster, or will fast hz application work with lm2576 psu; how much hz then ultimately? 4ns...
 

crutschow

Joined Mar 14, 2008
34,285
4ns would be considered fast recovery but Schottkys are generally faster. It isn't the frequency of the switching that's as important as the switch speed (how long it takes to go from OFF to ON or ON to OFF).

If you look at the typical circuit schematic in the data sheet for the LM2576, you will see that it uses a 1N5822 Schottky for the free wheeling diode that conducts the current through L1 when the internal switch is OFF.
 

Thread Starter

Chillum

Joined Nov 13, 2014
546
4ns would be considered fast recovery but Schottkys are generally faster. It isn't the frequency of the switching that's as important as the switch speed (how long it takes to go from OFF to ON or ON to OFF).

If you look at the typical circuit schematic in the data sheet for the LM2576, you will see that it uses a 1N5822 Schottky for the free wheeling diode that conducts the current through L1 when the internal switch is OFF.
another forum member suggested that I buy sr360 cause I have 36v power supply and the 1n5822 only 40v (inductance thread) will sr360 work?
 
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