Schottky

Discussion in 'General Electronics Chat' started by Chillum, Dec 12, 2014.

  1. Chillum

    Thread Starter Active Member

    Nov 13, 2014
    546
    9
    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: -)
     
  2. Chillum

    Thread Starter Active Member

    Nov 13, 2014
    546
    9
    sorry everyone finger trouble on phone, please see newer thread with same name
     
  3. Chillum

    Thread Starter Active Member

    Nov 13, 2014
    546
    9
    I'm purposefully creating new post to shift down erroneous post. reply to this one, please
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,137
    1,786
  5. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    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.
     
  6. Chillum

    Thread Starter Active Member

    Nov 13, 2014
    546
    9
    rectification? is that what in switch mode psu? I know how a four diode bridge works.
     
  7. Chillum

    Thread Starter Active Member

    Nov 13, 2014
    546
    9

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

    Expert

    Mar 14, 2008
    13,000
    3,229
    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.
     
  9. Chillum

    Thread Starter Active Member

    Nov 13, 2014
    546
    9
    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...
     
  10. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    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.
     
    ronv likes this.
  11. Chillum

    Thread Starter Active Member

    Nov 13, 2014
    546
    9
    another forum member suggested that I buy sr360 cause I have 36v power supply and the 1n5822 only 40v (inductance thread) will sr360 work?
     
  12. Chillum

    Thread Starter Active Member

    Nov 13, 2014
    546
    9
  13. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    The SR360 should work fine for that application.
     
  14. Chillum

    Thread Starter Active Member

    Nov 13, 2014
    546
    9
    thank you!
     
Loading...