Where does the power for USB (5V) come from in ATX systems?

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RigidStyle2020-10-09 07:13:53

Power Supply

RigidStyle, 2020-10-09 07:13:53

Where does the power for USB (5V) come from in ATX systems?
I mean, is the USB peripheral powered directly from the 5V PSU, or is there a 12V->5V converter on the board?

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3 answer(s)

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pfg21, 2020-10-09
@RigidStyle

all voltages are generated by the power supply and output to the ATX power connector
- three main high-current supply voltages 12v 5v 3.3v
- additional low-current -12v -5v are now practically not used.
- "standby" power supply 5v
- a few more signal wires
if you need supply voltages of a different level, they are formed from the supply voltages on the motherboard, this is usually the power supply for the processor, chipset and memory.
5 volts goes directly to the usb from the power supply,
and usually there is a USBPW switch on the motherboard that allows you to power the usb either from the "regular" + 5v or from the on-duty + 5v (then when the computer is turned off, the usb power is not turned off).

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VT100, 2020-10-09
@VT100

Previously (10-15 years) there were jumpers on desktop mobos. USB came either from the main line 5 V, or from 5 Vsb. I think - little has changed, except for the type of switch.
On beeches, obviously, through an electronic switch and always through a switching regulator Vbat -> 5 V.

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Vladimir Korotenko, 2020-10-09
@firedragon

From the power supply. Suddenly yes?
It depends on each board, contact the developer for details.
In theory, there is only 3.3V in sleep mode