Switching Power Supply User Guide

Basic Concepts of Switching Power Supply

Switching power supplies utilize modern power electronics technology to control the duty cycle of switching transistors, maintaining a stable output voltage. They primarily consist of pulse width modulation (PWM) control ICs and MOSFETs, achieving high-efficiency power conversion through high-frequency switching operations.

This fundamentally differs from the operating principle of linear power supplies: the power transistors in switching power supplies operate in a switching state (fully on or fully off), rather than in the amplification region found in linear power supplies. This operating mode enables switching power supplies to typically achieve efficiencies of 80%-95%, whereas linear power supplies only reach 30%-40%.

Switching power supplies satisfy three fundamental operating conditions: power electronic devices operate in a switching state rather than a linear state; they operate at high frequencies rather than low frequencies near the mains frequency; and they deliver DC output.

Working Principle of Switching Power Supplies

1. Rectification and Filtering (AC-DC): The input AC power first passes through a rectifier bridge for rectification and a capacitor for filtering, yielding unregulated high-voltage DC (bus voltage).

2. High-Frequency Chopping (DC-AC): Power switching transistors (MOSFETs) conduct and turn off at extremely high frequencies (tens of kHz to several MHz), chopping the high-voltage DC into high-frequency pulsed square-wave voltage.

3. Power Transformation and Isolation (AC-AC): The high-frequency pulses are coupled to the secondary side via a transformer, achieving voltage transformation and electrical isolation.

4. Secondary Rectification and Filtering (AC-DC): The high-frequency AC square wave from the transformer's secondary winding passes through rectifier diodes and a filter network to produce a stable DC output.

5. Feedback Control (Voltage Regulation): The output voltage is sampled via a voltage divider resistor and compared to a reference voltage. The error signal is fed into the PWM controller, which dynamically adjusts the duty cycle to maintain stable output voltage.

Power Supplies Advantages

1.High efficiency (typically 80%-95%), reducing energy consumption and heat generation

2.Compact size, lightweight, and high power density

3.Wide input voltage range, accommodating unstable grid voltages

4.Flexible design enabling multiple outputs and positive/negative voltage outputs