Introduction to Switch-Mode Power Supply

A switch-mode power supply, also known as a switching power supply or switch-mode converter, is a high-frequency electrical energy conversion device. It is a type of power supply unit that converts an input voltage to the desired voltage or current required by the user through different structural forms.

Basic Components of a Switch-Mode Power Supply

01

• Main Circuit Inrush Current Limiting: Limits the inrush current on the input side when the power supply is turned on.
• Input Filter: Filters out noise from the power grid and prevents internal noise from feeding back into the grid.
• Rectification and Filtering: Converts the AC input from the power grid to a smoother DC voltage.
• Inverter: Converts the rectified DC voltage into high-frequency AC voltage, which is the core part of the high-frequency switch-mode power supply.
• Output Rectification and Filtering: Provides stable and reliable DC voltage according to the load requirements.

02 Control Circuit: The control circuit samples from the output side, compares it with the set value, and then adjusts the pulse width or frequency of the inverter to stabilize the output. Additionally, it uses data from the testing circuit and the protection circuit to implement various protection measures for the power supply.

03 Testing Circuit: Provides various parameters and instrumentation data for the protection circuit during operation.

04 Auxiliary Power Supply: Powers the software (remote) startup of the power supply to supply power to the protection circuit and control circuits (such as PWM chips).

Basic Working Principle of a Switch-Mode Voltage Regulator

Switch-mode voltage regulators can be controlled in two ways: pulse width modulation (PWM) and frequency modulation. In practical applications, pulse width modulation (PWM) is more commonly used, and most of the integrated circuits for switch-mode power supplies currently developed and used are of the PWM type.

The basic principle of a pulse width modulation-based switch-mode voltage regulator is shown in the diagram below.

For a unipolar rectangular pulse, the DC average voltage Uo depends on the width of the pulse. The wider the pulse, the higher the DC average voltage value. The DC average voltage Uo can be calculated using the following formula:

Uo=Um×T1/T

Where:

• Um is the maximum voltage of the rectangular pulse,
• T is the period of the rectangular pulse,
• T1 is the width of the rectangular pulse.

From this equation, it can be seen that when Um and T are constant, the DC average voltage Uo​ is directly proportional to the pulse width T1. Therefore, by making the pulse width narrower as the output voltage of the regulator increases, we can achieve a stable output voltage.

Analysis of the Development Direction of Switch Mode Power Supplies

The trend in the development of switch mode power supplies (SMPS) is towards higher frequency. High-frequency operation enables SMPS to be more compact and opens up broader application areas, especially in high-tech fields, thus driving the advancement of SMPS technology, with a focus on achieving lighter, smaller, thinner, lower noise, higher reliability, and better anti-interference capabilities.

Switch mode power supplies can be divided into two main categories: AC/DC and DC/DC. DC/DC converters have already achieved modularization, with design technologies and manufacturing processes gaining wide acceptance from users. However, the modularization of AC/DC power supplies faces more complex technical and manufacturing challenges due to their inherent characteristics.

Furthermore, the development and application of switch mode power supplies play an important role in energy conservation, resource saving, and environmental protection. The main power electronic devices used in switch mode power supplies include diodes, IGBTs, MOSFETs, and transformers.