Power Supply Units (PSU) Essentials

Role of the Power Supply Unit - Converts wall-socket $AC$ into low-voltage $DC$ for all PC components. - Supplies steady voltages; critical for system stability. ## AC vs. DC Characteristics - Household power: $AC$ cycles between positive & negative.- USA: $110\text{–}120\,V$ at $60\,Hz$. - Europe/Asia: $230\text{–}240\,V$ (50 Hz typical). - Components require constant $DC$ (e.g., battery: $1.5\,V\,DC$ always positive). ## Voltage Levels Delivered - After conversion, PSU outputs multiple rails $\le 12\,V$ $DC$. ## Internal PSU Elements - Transformer: large voltage drop (e.g., $120\,V$ $AC$

Physical Size & Power Ratings - Small office PC: PSU $\approx$ fist-size. - Gaming/workstation: larger units (2–4$\times$ volume) for higher wattage. ## Installation Basics - Mounted with four screws; external plug faces case rear. - Internal cables connect CPU, motherboard, drives, GPUs. ## Modular vs. Non-Modular - Non-modular: all cables permanently attached. - Modular: detachable cables; improves airflow & reduces clutter. - Power delivery identical; choice affects cable management only. ## Redundant Power Supplies - Some servers/workstations use two PSUs + supporting motherboard/backplane. - Provides fail-over: if one PSU fails, the other maintains operation; hot-swappable. - Typical desktops use a single PSU.