SCR protection

Discussion in 'General Electronics Chat' started by Skeebopstop, Feb 5, 2009.

  1. Skeebopstop

    Thread Starter Active Member

    Jan 9, 2009
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    Is an SCR circuit like the one attached used on things other than series regulators?

    Surge protection would be better suited for other forms of protection. SMPS are too susceptible to startup spikes or load variation spikes to risk activating an SCR, so I wonder how they are used modern day.
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    I can't understand what exactly you want to ask.
    This circuit, is a crowbar circuit which protects the load from over voltages. If the voltage across the SCR rises above a specified limit determined by the zener diode then the zener will conduct and turn on the SCR. The SCR will short the power supply lines and blow the protective fuse or trip an over current circuit. If there is no fuse or overload protection then you can't use it.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    The design philosophy of a crowbar is it is better to blow the power supply before it blows whatever it is powering. It is the cheapest block, almost always.
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    If you are interested in one there are ready ICs which perform this function.
     
  5. Skeebopstop

    Thread Starter Active Member

    Jan 9, 2009
    358
    3
    I guess I am used to seeing MOV for overvolatge/surge protection to cause the fuse to blow, however on second thought, MOVs take quite some voltage change to really start conducting, where as a crowbar can be set relatively accurately and at low voltages to blow your fuse.

    For example, if I started to 'overload' a SMPS flyback design, the voltages would only 'droop', so such an SCR circuit would be inappropriate. So I was more trying to figure out which 'types' of power rails are appropriate to crobar. Series regulators seemed appropriate as they start to let through high voltages during over current conditions so you want to crobar the fuse to keep the high voltage from creeping into the circuitry.
     
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