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# Can anyone explain how psu voltages work?

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• Cable
• Components
Last response: in Components
October 6, 2013 4:18:07 AM

Hi

This might seem a daft question but I'm confused by psu voltages. I understand most components use the 12v supply from the psu but some use 3.3v or 5v. I have my water pump, fan controller, SSD and HDD connected to a single output cable from the psu with multiple molex plugs and SATA adapters. I used the same cable for neatness. My Seasonic X-Series 650w psu has plenty other cables I could add. Everything works fine.

What I don't understand is how the same cable can supply the pump and fans, which are 12V, and the two drives, which are either 3.3v or 5v as far as I know, at the same time when they need different voltages. Am I missing something or doing something wrong?

Mag

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October 6, 2013 5:13:09 AM

The base voltage on the incoming cable is 12v. Each of the connected components will have either a direct path to that component (in the case of 12v components) or will have a voltage dropping circuit (resistors) prior to passing the voltage on.

Basically, each component has either a straight pass through for the power, or a modifying circuit that "drops" the voltage prior to use.

EDIT: Also, the leads from your m/b to the various components (sata cables, etc) originate from the m/b on various headers. These headers already have the correct voltages (created by drops within the m/b) and the pinouts on the connectors carry the correct voltages to the components.

Mark
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October 6, 2013 7:18:32 AM

markwp said:
The base voltage on the incoming cable is 12v. Each of the connected components will have either a direct path to that component (in the case of 12v components) or will have a voltage dropping circuit (resistors) prior to passing the voltage on.

Basically, each component has either a straight pass through for the power, or a modifying circuit that "drops" the voltage prior to use.

EDIT: Also, the leads from your m/b to the various components (sata cables, etc) originate from the m/b on various headers. These headers already have the correct voltages (created by drops within the m/b) and the pinouts on the connectors carry the correct voltages to the components.

Mark

Thanks Mark, that makes sense now.

Mag
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October 8, 2013 5:09:42 AM

You're welcome!
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