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Thread: Single rail ocp protection

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    Default Single rail ocp protection

    Hi
    from what i read OCP, SCP, OVP are the necessary protections that the ATX specification demands.
    i notice that many good psu with single rail don't have ocp.
    that o.k.? the demand is for single rail too?
    for example
    http://www.jonnyguru.com/modules.php...Story&reid=185

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    Quote Originally Posted by none77 View Post
    i notice that many good psu with single rail don't have ocp.
    that o.k.? the demand is for single rail too?
    As far as I know unlikely a single-rail PSU can have OCP: OCP is usually the way a single-rail is splitted into multi-rails (you may give a read to this long but useful thread).
    So, is that ok? Talking just about safety, probably no, probably a properly designed multi-rails PSU offer an higher grade of electrical safety for you and your PC, particularly speaking about high power units.
    Best, Luca

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    Default

    I notice that most of them don't have.
    my question is a single rail psu should have ocp according to atx standard.
    thanx

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    Quote Originally Posted by none77 View Post
    I notice that most of them don't have.
    my question is a single rail psu should have ocp according to atx standard.
    As far as I know, single rail PSUs should not be ATX compliant, strictly speaking.
    By the way, if I didn't misunderstand, ATX specs always require OCP: particularly, the ATX PSU Design Guide v. 1.31 requires at least two 12V rails (the 12V2 dedicated to the CPU, if I recall correctly), each with separated current limit (see paragraph 3.5).
    Best, Luca

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    Default

    Single +12V rail PSUs typically use OPP in lieu of OCP.
    Last edited by Jon Gerow; 03-02-2015 at 02:22 PM.

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    Quote Originally Posted by jonnyGURU View Post
    Single +12V rail PSUs typically use OPP in lieu of OCP.
    But does the ATX 1.31 require OCP always?
    Last edited by Jon Gerow; 03-02-2015 at 02:22 PM.
    Best, Luca

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    Some single rail PSUs implement +12V OCP in the same fashion as multi-rail, just using a single shunt resistor (or several ganged in parallel) instead of having multiple separate ones. The V series, for instance, has a single rail OCP, with a spot on the back of the PCB for two very large SMT shunt resistors connected in parallel, though I believe the V700 only populated one of them.

    OPP is generally a primary side protection, usually using measured current on the post-PFC ~400V DC bus. Since the DC bus is buffered by the primary capacitors, it has quite a lot of "inertia", so a rapid change on the output (such as a short circuit) will take some extra milliseconds to cause a measurable change. Therefore OPP is necessarily slower than OCP. This isn't desirable. Also, some manufacturers seem to feel that actual OPP is unnecessary, and simply rely on the input fuse to fill that role.
    Last edited by CM Phaedrus; 03-02-2015 at 12:33 PM.

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    Quote Originally Posted by CM Phaedrus View Post
    Some single rail PSUs implement +12V OCP in the same fashion as multi-rail, just using a single shunt resistor (or several ganged in parallel) instead of having multiple separate ones. The V series, for instance, has a single rail OCP, with a spot on the back of the PCB for two very large SMT shunt resistors connected in parallel, though I believe the V700 only populated one of them.

    OPP is generally a primary side protection, usually using measured current on the post-PFC ~400V DC bus. Since the DC bus is buffered by the primary capacitors, it has quite a lot of "inertia", so a rapid change on the output (such as a short circuit) will take some extra milliseconds to cause a measurable change. Therefore OPP is necessarily slower than OCP. This isn't desirable. Also, some manufacturers seem to feel that actual OPP is unnecessary, and simply rely on the input fuse to fill that roll.
    But when the ATX 1.31 requires OCP, does it mean there should be a current limiter (as on Vanguard-series), or that such a protection may be obtained "indirectly" (for instance through the OPP, which AFAIK is not required by ATX specs, as pointed out by Jon)?
    Best, Luca

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    ATX 1.31 is obsolete. The standards you want are ATX12V 2.3 and EPS12V 2.92. I don't believe either of them currently require +12V OCP.

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    Default

    the link was o.k.
    look at the end, extrenal links
    http://en.wikipedia.org/wiki/ATX

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