Desktop Motherboard Power Sequence Pdf May 2026
The power sequence of a desktop motherboard is a strict, step-by-step electronic "handshake" between the Power Supply Unit (PSU) and the motherboard's controllers to ensure all voltages are stable before the CPU begins executing code Typical Power-On Sequence Standby Power (5VSB):
- PS_ON# goes low → +12V rises after 50ms.
- PWR_OK rises 200ms after +12V stable.
- Only after PWR_OK does memory power turn on.
- VCORE begins after VCORE_EN and ramps over 5ms.
- Platform reset is the last to de-assert.
Before you ever press the power button, certain "always-on" voltages are live on the motherboard as soon as the power supply is plugged in and switched on. desktop motherboard power sequence pdf
lines. Power is delivered to the RAM first, followed by the Chipset (PCH/North Bridge). VCORE & VRM Activation: The power sequence of a desktop motherboard is
7) References to consult (for PDF creation)
- Intel/AMD platform design guides (VRM and sequencing recommendations).
- ATX12V / ATX power supply specification (for PS_ON# and PWR_OK semantics).
- Motherboard vendor schematics and VRM datasheets for exact timings.
- Embedded Controller / Super I/O datasheets for button/standby handling.
System Reset (PLTRST# / CPURST#): The PCH releases the "Reset" signal, which clears junk data from the chips and allows the CPU to start executing instructions. 5. BIOS and POST PS_ON# goes low → +12V rises after 50ms
Introduction to the Power Sequence