DC Power Supply Question

Oct 10, 2005 30 Replies
A
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[...]

Huh? The AC component will pass the capacitor, whether the capacitor is pre-charged to some AC level or not.

In fact, the DC charge will bias the capacitor so that it doesn't have to be non-polar.

Anno

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P

"kell"

** They are usually called " battery chargers " .
** Most DMMs allow you to measure the AC ripple on a DC supply directly using the AC volts ranges.
** Don't the poor folk live in those things ?

.......... Phil

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A

Phil Allison wrote in sci.electronics.design:

We're looking at this circuit:

C o----|>|----o----||----+ | | ~ CS --- R | | --- | | | | o-----------o----------

where the capacitor CS may be present or not.

Please explain how the AC current through R depends on the DC charge in capacitor C, and why C has to be non-polar.

Anno

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J

Once the cap charges up to the rectifier peak voltage, the diodes stay off, so there is no AC applied to the capacitor, which is effectively disconnected from the transformer.

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A

Phil Allison wrote in sci.electronics.design:

So you concede that both questions have to be answered the way I imply. Apparently we don't agree what the "situation" is. I'll live with that.

The behavior of the simple circuit you snipped is obvious without trying. I guess I'll rather piss off, this isn't going anywhere.

Anno

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P

"Anno Siegel"

** Err - no it will not in this case.

What John posted was spot on.

** Pure gobbledegook.

........ Phil

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A

Oh, right, there is no load, so no ripple to pass the capacitor. I was assuming an invisible (DC-)load. Sorry.

Anno

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P

"Anno Siegel"

** Neither query is relevant to the situation.

Go try it - or piss off f****it.

....... Phil

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P

"Anno Siegel"

** = A schizo.

......... Pphil

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I

Getting there. I've got a 5V 0.4A supply that was purchased with a USB hub for about $8 US all-in. Admittedly it needed an input resovoir capacitor, but after that, it works fine up to about 0.5A.

If the cap was added in at the factory, this'd be a reasonably acceptible

100-240V 2.5W 5V PSU, for well under $4.
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K

D'oh! I didn't even draw a diagram before I posted.

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