ATX Power Supply values

Mattew Michalicka's picture

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Joined: May 17, 2020

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ATX Power Supply values
May 17, 2020 - 7:46pm

Hi, I have an old Power supply from pc and Its working. But, I have to do some changes to make output regulated. So, I have to measure some things and calculate Voltage at the end. I cannot find any Formula for calculating it. Plese can someone calculate it for me?Bez názvu.png

jaksonlee's picture

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When high-powered GPUs were
May 17, 2020 - 10:17pm

When high-powered GPUs were first introduced, typical ATX power supplies were "5 V-heavy", and could only supply 50–60% of their output in the form of 12 V power. Thus, GPU manufacturers, to ensure 200–250 W of 12 V power (peak load, CPU+GPU), recommended power supplies of 500–600 W or higher.

The ATX specification defines the Power-Good signal as a +5-volt (V) signal generated in the power supply when it has passed its internal self-tests and the outputs have stabilized. This normally takes between 0.1 and 0.5 seconds after the power supply is switched on. The signal is then sent to the motherboard, where it is received by the processor timer chip that controls the reset line to the processor.
The ATX specification requires that the power-good signal go high no sooner than 100 ms after the power rails have stabilized, and remain high for 16 ms after loss of AC power, and fall at least 1 ms before the power rails fall out of specification.

Cheaper and/or lower quality power supplies do not follow the ATX specification of a separate monitoring circuit; they instead wire the power good output to one of the 5 V lines. This means the processor will never reset given bad power unless the 5 V line drops low enough to turn off the trigger, which could be too low for proper operation.

Olivia Williams's picture

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When high-powered GPUs were
September 28, 2020 - 1:51pm

When high-powered GPUs were first introduced, typical ATX power supplies were "5 V-heavy", and could only supply 50–60% of their output in the form of 12 V power. Thus, GPU manufacturers, to ensure 200–250 W of 12 V power, recommended power supplies of 500–600 W or higher.

Sourav Gupta's picture

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Hii
September 28, 2020 - 6:06pm

what is the load? if nothing is connected then the voltage will be 12V.