A power source is a device that generates or converts electrical energy for human use. The utilization of electrical energy is a hallmark of modern science and technology and social progress. Modern society's national economy, superstructure, and even people's daily lives—clothing, food, housing, and transportation—all rely on power sources, such as cultural entertainment, office work and study, scientific research, industrial and agricultural production, national defense, education, environmental protection, medical and health services, transportation, lighting, communication, and space exploration, among others.
Nature does not have directly usable power sources. While natural phenomena like lightning generate some electrical energy, it is currently difficult to utilize as a power source. Therefore, the LED switching power supplies used by humans are all converted from mechanical energy, electrical energy, chemical energy, nuclear energy, etc. This type of power source, obtained through the conversion of other energy sources, is usually called a power source that generates electrical energy, such as generators and batteries. The vast majority of electricity is produced and transmitted by power plants, known as mains power.
Some electrical devices, such as incandescent lamps, electric stoves, and AC motors, can operate simply by being connected to mains power. While electronic devices such as computers, televisions, and X-ray machines are powered by mains electricity, they all incorporate power conversion circuits (devices) to convert the sinusoidal AC mains power into the required DC, high-voltage, or pulsed power. On islands and ships where mains electricity is unavailable, batteries can be converted to AC power, enabling computers and instruments to operate normally. Satellites and spacecraft in space collect solar energy and convert it to various types of electrical energy to sustain long-term operation. Electrical energy is a precious resource that needs to be cherished and conserved. Energy-saving fluorescent lamps and high-efficiency HID lamps use electronic ballasts with power factor correction and high-frequency processing, saving electricity and purifying the power grid. The input power of AC motors undergoes frequency conversion, a process known as variable frequency speed control, to optimize motor efficiency. Besides hydropower, thermal power, and nuclear power, solar energy, wind power, biogas, tidal energy, bioenergy, and chemical energy are also used to generate electricity in specific environments as a supplement to conventional power. These supplementary power generation units require DC/DC and DC/AC power conversion for easy storage and conversion into a sine wave consistent with the grid frequency. Grid instability can cause numerous problems for electrical equipment, even preventing it from functioning properly; solar and wind power are affected by seasons and weather, resulting in unstable electricity generation, necessitating voltage stabilization in many situations, which also requires power conversion and adjustment. Power conversion transforms one form of electrical energy into another, which can be a conversion between AC and DC, a change in voltage or current amplitude, or a change in the frequency or phase of AC. In some cases, power conversion may simply improve stability or certain performance characteristics. In power conversion, the power source input is also electrical energy; such a power source, where both input and output are electrical energy, is called a power conversion power source. This type of power source uses power conversion technology to convert primary electrical energy from mains power or batteries into secondary electrical energy suitable for various electrical applications.
The aforementioned power conversion mainly involves voltage transformation, voltage regulation and rectification, filtering, stabilization, and conversion. These basic power conversions are achieved through a series of technical methods, each suitable for different environmental conditions and requirements. From this perspective, power supply technology studies the technology of power conversion.
1. Voltage Transformation
Transformers are the most commonly used devices for AC voltage transformation. Phase control, linear compensation, frequency conversion, and time division (pulse width modulation, i.e., PWM) can all achieve AC voltage transformation. The most common method for DC voltage transformation is DC/DC conversion, while passive and active voltage dividers are relatively simple methods commonly used for low-power DC voltage transformation.
2. Voltage Regulation
Voltage regulation can be achieved by adding step and continuous settings to the voltage transformation. Depending on the needs, voltage regulation can be manual, automatic, or remotely controlled.
3. Rectification
Rectification is the earliest method for converting AC to DC. Using unidirectional passive devices is the simplest way to achieve rectification, while using active switching synchronous rectifiers can minimize rectifier losses.
4. Filtering
Filtering is the process of converting unidirectional pulsating current into smooth direct current, which can be achieved through passive or active filter circuits.
5. Stabilization
Introducing methods such as automatic negative feedback control into the power supply can stabilize the output. If the feedback quantities are voltage, current, power, frequency, and phase, then a stable power supply with stable voltage, stable current, constant power, stable frequency, and stable phase can be obtained accordingly.
6. Transformation
Transformation specifically means changing from one state to another. Examples include the conversion between AC and DC; waveform conversion such as sine waves, square waves, triangular waves, trapezoidal waves, pulse waves, and special waves; and the conversion between light, heat, mechanical, wind, magnetic, and physical/chemical energy and electrical energy.
Power conversion involves numerous technologies, commonly including parametric voltage regulation, linear feedback voltage regulation, magnetic amplification, digitally controlled voltage regulation, phase control, frequency conversion, pulse width modulation (PWM), sinusoidal pulse width modulation (SPWM), soft-switching PWM, phase-shifted resonance, reactive power compensation, power factor correction (PFC), phase splitting, current sharing, sensor sampling, drive protection, energy storage, charging, anti-interference, and electromagnetic compatibility. Practical needs drive the continuous development and advancement of these technologies, enabling power supply devices to meet the diverse requirements of various loads.
Today, power supply technology integrates knowledge from electronics, power integration, automatic control, materials, sensing, computers, electromagnetic compatibility, and thermal engineering, evolving from a marginal interdisciplinary field into a unique branch of power (electric) electronics.
Power supply technology is also highly practical, serving a wide variety of loads across various industries and fields. Their performance characteristics and the technologies employed vary greatly, making the scope of power supply technology extremely rich. This book only studies and introduces the relevant technologies of power supplies used in commonly used electronic instruments and equipment, as well as basic communication power supplies. Waterproof switching power supply, LED power adapter, waterproof LED power adapter, LED driver power supply, transformer, power adapter, waterproof transformer