The PCH sends a signal to the PSU to turn on the main rails (3.3V, 5V, 12V) by pulling the PS-ON# line low (green wire).
The PCH raises the SLP_S4# (Sleep S4) and SLP_S3# (Sleep S3) signals to high (3.3V). These signals act as the green light to enable system-wide power conversion (turning on the RAM, PCH, and CPU power rails). 4. System Power Rails (Buck Converters) +3VSpositive 3 cap V sub cap S +5VSpositive 5 cap V sub cap S +12VSpositive 12 cap V sub cap S desktop motherboard power sequence pdf exclusive
Before you even touch the power button, certain "Always-On" voltages must be present. +5V Standby (+5VSB): The PCH sends a signal to the PSU
The power management ICs start generating smaller, precise voltages for the CPU ( precise voltages for the CPU (