Complete Guide to Switching Power Supplies: How They Work and How to Choose

Comprehensively explains the basics, mechanisms, selection points, 24V/12V application examples, and noise countermeasures of switching power supplies. Packed with information that beginner to intermediate engineers want to know. Please also check out our Unifive product introductions and support system.

What is a Switching Power Supply? Easy-to-Understand Explanation of Basic Mechanism and Usage Points

For engineers and designers of electrical and electronic devices, the switching power supply is an essential component to achieve high efficiency, miniaturization, and cost reduction. This article provides a comprehensive explanation of the basic mechanism and operating principles of switching power supplies, selection methods for different applications, noise countermeasures, safety standards, and other important points. It is summarized to be accessible for beginners and mid-level engineers, as well as those new to power supply design, so be sure to read to the end.

History of Switching Power Supplies

The history of switching power supplies dates back to the 1800s.

Some say that IBM was the first to develop a switching power supply in 1958. The one designed by IBM at the time was based on vacuum tube technology. Around the same time, GM filed a similar patent as a transistor oscillator, which is said to have significantly expanded the options available to equipment designers. The 1960s were a very active time across the space, communications, electronics, and computer industries.

How Switching Power Supplies Work

* Example of a basic block diagram of a switching power supply

A switching power supply is a power converter that converts the AC input into DC through rectification, and then controls voltage using high-frequency switching elements (such as MOSFETs) turned on and off at high speed. Compared to linear regulators, it has the following major characteristics:

• High efficiency: Only the necessary power is supplied through switching operation, minimizing ripple and heat generation.
• Miniaturization: High-frequency operation allows for smaller transformers and filter components, saving board space.
• Wide input voltage support: Many models can support from 100V to 200V depending on control circuits.

The basic operating principle follows this flow: AC input → rectification circuit → high-frequency switching circuit (e.g., PWM control) → isolation transformer (if needed) → rectification and smoothing → output. PWM (Pulse Width Modulation) is used to maintain stable output voltage and current, and many units include protective features against overvoltage and overcurrent.

Difference Between Switching and Linear Power Supplies

A switching regulator is often compared with a linear power supply (series regulator). A linear power supply uses transistors or regulator ICs to step down voltage, producing less high-frequency noise and being simpler to design, but it has the following drawbacks:

• Low efficiency: Excess power is mostly dissipated as heat, requiring cooling measures like heat sinks.
• Large and heavy: Requires large transformers and heat dissipators.

* Comparison table of switching vs. linear power supplies

Switching power supplies may require noise suppression, but their compact and lightweight design combined with high efficiency is a major advantage.
Check the following points when selecting a unit:

1. Range of output voltage and current
2. Input voltage range (AC/DC)
3. Efficiency, heat output, and cooling method
4. Noise characteristics
5. Protective functions (overvoltage, overcurrent protection, etc.)
6. Size, weight, and cost

Why Switching Power Supplies Are Efficient

Switching power supplies have high efficiency because the switching element operates only in fully on or fully off states, with minimal operation in intermediate voltages. Unlike a linear power supply that continuously generates loss, switching types generate less heat and contribute to energy saving.

By adjusting the switching frequency or pulse width according to load changes, they maintain efficiency even in standby or low-load conditions, which is also a major advantage.

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