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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 3rd Dec 2017, 2:53 pm   #1
astral highway
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Default PC SMPS component ID?

You know the bog standard PC SMPS, often in a grey case with a kettle lead?
Usually something like 13A @12V and 5V supplies?

I notice there is a component beneath the kettle lead in connector. It says 230v on the outside but is not a voltage setting. I think it is a thermal overload of some kind. It reads O/C on a multimeter. Hence I wonder if it is a binary device that switches on above a certain temperature, enabling a shut-down circuit to be activated?

I am just using an old case for another project and am deciding whether to keep this component, alongside the useful RFI measures on board.
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Old 3rd Dec 2017, 3:20 pm   #2
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Default Re: PC SMPS component ID?

I think you'll need to give us a picture. Lots of components could say '230V' on the outside. The most obvious would be the mains voltage selector switch, but few PC power supplies have one of those these days.

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Old 3rd Dec 2017, 3:23 pm   #3
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Default Re: PC SMPS component ID?

It’s usually a red slide switch of some description. Might be fixed in some of the cheaper ones. Usually switches the inlet diode/capacitor arrangement.
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Old 3rd Dec 2017, 3:49 pm   #4
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Default Re: PC SMPS component ID?

Quote:
Originally Posted by MrBungle View Post
Itís usually a red slide switch of some description. Might be fixed in some of the cheaper ones.

Ah, that sounds possible. Thank you.
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Old 3rd Dec 2017, 3:50 pm   #5
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Default Re: PC SMPS component ID?

Quote:
Originally Posted by cmjones01 View Post
I think you'll need to give us a picture.
I wanted to, but frustratingly I can't upload photos from my iPhone to gmail at the moment, and that's the only way I can post them on the site...
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Old 3rd Dec 2017, 5:03 pm   #6
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Default Re: PC SMPS component ID?

Yes, as MrBungle says, if it's a red slide switch, it's the voltage selector. It's wired so that it changes the input arrangement from a bridge rectifier with both reservoir capacitors in series on 230V, to a voltage doubler on 115V. That way the half-bridge primary side of the power supply always has a 300V-ish supply with a centre tap (for high frequency switching purposes) at the junction of the two reservoir capacitors. I've always thought it quite a neat arrangement. I'm assuming that it's been made obsolete by the advent of power-factor-correcting input stages which don't work that way.

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Old 3rd Dec 2017, 6:02 pm   #7
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Default Re: PC SMPS component ID?

Quote:
Yes, as MrBungle says, if it's a red slide switch, it's the voltage selector. It's wired so that it changes the input arrangement from a bridge rectifier with both reservoir capacitors in series on 230V, to a voltage doubler on 115V. That way the half-bridge primary side of the power supply always has a 300V-ish supply with a centre tap (for high frequency switching purposes) at the junction of the two reservoir capacitors.
Very neat idea indeed! Thanks for de-mystifying.
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Old 3rd Dec 2017, 6:21 pm   #8
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Default Re: PC SMPS component ID?

This I'm guessing
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Old 3rd Dec 2017, 6:26 pm   #9
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Default Re: PC SMPS component ID?

Truth is, pretty much all of the PC-type SMPS I've seen for the last decade have dealt with the issue of 110/220V switching by themselves and not had a separate user-accessible switch for this.
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Old 3rd Dec 2017, 7:35 pm   #10
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Default Re: PC SMPS component ID?

An ATX PSU from a Dr. Dre Beatbox on which I'm working (see seperate thread for details) has two points on it's PCB marked 110 & 230v and designed as described by Chris Jones in post #6, but no switch is, or ever has been, fitted to it.
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Old 3rd Dec 2017, 7:45 pm   #11
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Default Re: PC SMPS component ID?

Most of them will work from about 90 to 265v. They also work fine on DC; I’ve brought a smaller switcher up on three bench supplies in series. Amazingly robust little things.
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