How Computer Power Supply Voltages Are Generated

A computer power supply unit (PSU) converts AC mains voltage (typically 220V or 110V) into several DC voltages required for different components of a computer. 

What is ATX?

ATX (Advanced Technology eXtended) is a standard developed by Intel in 1995 for motherboards, computer cases, and power supplies. It defines the size, connector placement, and cooling system requirements for PC components.

1. ATX Motherboard Form Factor

A standard ATX motherboard measures 305 × 244 mm. Variants include:

• Micro-ATX (244 × 244 mm) – smaller, fewer expansion slots.
• Mini-ITX (170 × 170 mm) – compact, designed for small PCs.

2. ATX Power Connectors

• 24-pin main power connector – supplies power to the motherboard.
• 4/8-pin EPS12V connector – additional power for the CPU.
• SATA and Molex connectors – for storage devices and peripherals.
• PCIe 6/8-pin connectors – for high-performance GPUs.

3. ATX Power Supply

ATX power supplies follow standard voltage outputs:

• +12V – for the CPU, GPU, fans, and drives.
• +5V – for older devices and USB ports.
• +3.3V – for RAM and motherboard circuits.
• +5VSB – standby power for USB and wake functions.

4. Cooling and Case Design

• Standardized airflow direction optimizes cooling efficiency.
• ATX cases support multiple fans and airflow configurations.

Advantages of ATX

• Compatibility – Components are interchangeable.
• Expandability – Multiple PCIe slots, RAM slots, and storage options.
• Modularity – Easy to upgrade or replace parts.

ATX remains the most widely used standard for desktop PCs, ensuring flexibility and scalability for different system configurations.

How Computer Power Supply Voltages Are Generated

Here’s how the main voltages are generated in an ATX power supply:

1. Input Rectification and Filtering

• The AC mains voltage is first passed through a bridge rectifier, converting it into pulsating DC (~310V DC from 220V AC input).
• Large capacitors smooth the rectified voltage.

2. High-Frequency Conversion

• A switching MOSFET and PWM controller chop the DC voltage at high frequency (20–100 kHz), supplying it to a high-frequency transformer.
• The transformer reduces the voltage and provides separate outputs for different voltage levels.

3. Output Rectification and Filtering

• The secondary windings of the transformer generate voltages like +12V, +5V, and +3.3V.
• Schottky diodes rectify the voltages, and capacitors filter out ripples.

4. Standby Power (+5VSB Generation)

• A small separate circuit generates +5V Standby (5VSB), allowing the computer to power certain components even when turned off.

5. Voltage Regulation and Protection

• Additional circuits regulate output voltages to maintain stability.
• Built-in protection mechanisms prevent overvoltage, overcurrent, and short circuits.

Main ATX Power Supply Voltages

The ATX power supply uses a switching power supply (SMPS) design, which makes it compact, efficient, and capable of providing stable voltages for modern computers.