the fundamental elements of a switching power supply
Introduction to switching power supply
The working process of a switching power supply is quite easy to understand, and it has three distinct features:
Switches: Power electronics operate in a switching state rather than a linear state
High frequency: power electronic devices work at high frequency instead of low frequency close to industrial frequency
DC: The switching power supply outputs DC instead of AC, and can also output high-frequency AC such as electronic transformers
Basic components of switching power supply
Switching power supply classification:
Switching power supply is divided into many types according to the topology: buck boost forward flyback half-bridge full-bridge LLC, etc., but in essence, there are only two working modes of switching power supply: forward: it transmits energy when the switch tube is turned on, and flyback: Energy is transferred when the switch is off.
Key circuit calculations:
Power conversion is a key part of the design, and its design process mainly includes the selection of power components and the design of switching transformers. Among them, the design of switching transformers is the most important part of the design work of switching power supplies. The design results directly determine the performance of switching power supplies. This paper mainly Explain the principle of the circuit.
power protection circuit
1. In the case of a short circuit at the output terminal, the PWM control circuit can limit the output current within a safe range. It can use a variety of methods to realize the current limiting circuit. When the power current limiting does not work in a short circuit, only another Add some circuits.
EMI Generation Mechanism and Restraint of Switching Power Supply
Switching power supplies are developing rapidly in the direction of high frequency and high efficiency. EMI suppression has become an important indicator of switching power supply design. Electromagnetic interference (EMI) is the lack of electromagnetic compatibility. It is the destructive electromagnetic energy from one electronic device to another through conduction or radiation. device process. In recent years, switching power supply has developed rapidly due to its advantages of high frequency, high efficiency, small size and stable output. Switching power supplies have gradually replaced linear regulated power supplies and are widely used in computer, communication, automatic control systems, household appliances and other fields. However, because the switching power supply works in a high frequency state and its high di/dt and high dv/dt, the switching power supply has very prominent shortcomings-it is easy to generate relatively strong electromagnetic interference (EMI) signals. EMI signals not only have a wide frequency range, but also have a certain amplitude, which will pollute the electromagnetic environment through conduction and radiation, and cause interference to communication equipment and electronic products. Therefore, how to reduce or even eliminate the EMI problem in switching power supply has become a problem that switching power supply designers are very concerned about. This article focuses on four methods of suppressing EMI of switching tubes and diodes in switching power supplies.
