Why is SCR called SCR?

Discussion in 'The Projects Forum' started by MMH, Feb 8, 2013.

  1. MMH

    Thread Starter Member

    Feb 8, 2013
    Hello Everybody! I am new to this forum. I want to ask you why a thyristor is called a rectifier. Is it because it acts as a Diode to some extent- it has an anode and a cathode. ?

    Thanks in advance for your help!!

    Well-Known Member

    Mar 1, 2012
    a thyristor and rectifier are two totally different things. They are not at all the same.

    a rectifier is 4 diodes used to turn AC into DC. A Thyristor is a protection device almost like a fuse/breaker.
  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
    That's close. A full explanation is here: http://www.allaboutcircuits.com/vol_3/chpt_7/5.html
  4. strantor

    AAC Fanatic!

    Oct 3, 2010
    A full wave bridge rectifier is what you described. A rectifier can be be a single diode, or any other of many types of components that can be used to rectify. Even a mosfet can be used as a rectifier. a DC generator is a mechanical rectifier.
    Ah... I guess our experiences with SCR/thyristors is a little different. I'm not sure what you've seen, but what I've seen is that they're used mostly for AC power control, not for protection. Actually I'm not sure how you would even use one for protection. Wouldn't seem like a good idea to me, as their common failure mode is shorted.
  5. t06afre

    AAC Fanatic!

    May 11, 2009
    Google crowbar circuit. It is common to use thyristors in such a circuit. However I do not think this circuit are very common to day. It was more a circuit used in CRT TVs
    #12 likes this.

    Well-Known Member

    Mar 1, 2012
    Yeah I was just trying to keep it simple, I don't know a lot about SCRs except the crowbar circuit and that's because we spent an entire class discussing a crowbar circuit lol.

    Thyristors can be used for protection to specifically blow a fuse. There was a thread on here in the last week where it was used in exactly that fashion and a picture was posted.

    I don't exactly understand it, but basically the thryistor goes across the AC lines, and in the event it gets too hot it shorts to blow the main fuse, also works for surges......but like I said, I don't understand why it's used that way.
  7. MrChips


    Oct 2, 2009
    The original SCR is uni-directional and hence qualifies as a rectifier.

    An SCR used as a crow-bar to blow fuses is only one application of the SCR, and a minor one at that.
    An SCR is used to control AC current because you cannot use it to turn off DC current. Once an SCR is triggered you cannot turn it off unless the current is reduced to zero.

    Hence a triggered SCR can be turned off at the zero crossing of the AC current.
    SCRs, or more accurately, thyristors are used in power AC circuits, light dimmers etc.

    Check out SCRs on Wikipedia:

  8. strantor

    AAC Fanatic!

    Oct 3, 2010
    I think you're describing a thermistor.

    EDIT: never mind, I googled the crowbar circuit and I see what you're talking about.
  9. killivolt

    Distinguished Member

    Jan 10, 2010

    Thermistor is a thermal current sensing, what I've seen in dryers they short open. A thyristor is open until current is above it's current rating, and is a direct short to ground in a TV.

    I think:rolleyes:

    Edit: I just saw your Edit:

    Edit: Edit: silly me!
  10. MMH

    Thread Starter Member

    Feb 8, 2013
    Thank you Everyone ! Now I understand why it is called SCR.
  11. Brownout

    Well-Known Member

    Jan 10, 2012
    Now explain it to us.
  12. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Some early abbreviations (acronyms);
    GR = germanium rectifier
    SR = silicon rectifier (diode)
    SCR = silicon controlled rectifier (diode that can be controlled)
  13. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    The terms get blurred due to them becoming useful at the same time vacuum tubes of the same function were in wide use (Thyratron Thyristor tubes).

    TRIACs, DIACs and SCRs have functions like different "Thyristor tubes", so they are called "Thyristors" rather than transistors or other name.
  14. RamaD

    Senior Member

    Dec 4, 2009
    Absolutely. I was wondering about why the question is, when the name itself is very clear. Only after your answer I realized the expansion is probably not so popular!