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Thread: AC or DC coupling used in the turn-on transient test?

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    Default AC or DC coupling used in the turn-on transient test?

    Wolf, there's one thing that's been unclear to me. In your turn-on transient tests, is the scope DC-coupled or AC-coupled, and why?
    It's been a hard day's night and I've been working like a dog.

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    DC - same as the regular scope shots. Because I'm testing for DC spikes.

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    If it is DC-coupled the voltage should ramp up to the nominal value and never approach zero again. It shouldn't look like a "spike" or "peak".

    I guess the scope is configured as "AC coupled" then, since the ripple testing is most probably carried out in AC coupling mode. The resolution of o-scope isn't high enough to measure some tens of milli-volts with a 12Volt DC bias. If you don't change the coupling mode between turn-on transient and ripple tests then it's a problem.

    http://www.madshrimps.be/?action=get...10&articID=889

    Here is a scope shot of boot process of PSUs. The +12V waveform (the light blue trace) is a ramp. Two minor rails derived from DC/DC ramp up after the +12V is stablized.
    Last edited by Travis; 02-23-2010 at 12:02 AM.
    It's been a hard day's night and I've been working like a dog.

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    Yeah, it's AC - had too many days without power here this week leading to too many messages to post and units to test on the rare occasions the power has been on.

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    I feel it very necessary that you change the test configuration of turn-on transient test to DC-coupling. You will see how different the result is.
    It's been a hard day's night and I've been working like a dog.

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    Yeah, that does look to be a good idea.

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