Explanation of basic components of switching power supply
Introduction to Switching Power Supply
This document serves as a reinforcement training for Zhang Zhansong's advanced switching power supply design. Based on the planned arrangement, Shen Gong explained the transformer design. In this article, the transformer design principle is briefly introduced, with a focus on explaining the circuit working principle and the calculation and selection of key components in the design process.
The working process of a switching power supply is quite easy to understand, and it has three obvious characteristics:
Switch: Power electronic devices operate in a switch state rather than a linear state
High frequency: Power electronic devices operate at high frequencies rather than near power frequencies
Switching power supply classification:
Switching power supplies are divided into many types based on topology: buck boost forward flyback half bridge full bridge LLC, etc. However, fundamentally, switching power supplies only have two working modes: forward: transmitting energy when the switch is turned on, and flyback: transmitting energy when the switch is turned off.
Introduction to Flyback Switching Power Supply
Flyback is also known as an isolated buck boost circuit. Basic working principle: When the switch is turned on, the transformer stores energy, and when the switch is turned off, the stored energy is released. The flyback switching power supply can be divided into dual ended and single ended flyback based on the number of switch tubes.
According to the working mode of the flyback transformer, it can be divided into CCM and DCM mode flyback power supplies.
According to the control method, it can be divided into PFM and PWM flyback power supplies.
According to the generation method of the driving duty cycle, it can be divided into voltage type and current type flyback switching power supplies.
The flyback power supply we are going to talk about is precisely defined as a current type PWM single ended flyback power supply.
Current source PWM single ended flyback power supply
Advantages of this type of flyback power supply: simple structure, cheap price, suitable for low-power power supply.
The disadvantages of this type of flyback power supply are: small power, generally below 150W, large ripple, low voltage load adjustment rate, generally greater than 5%.
The main difficulty in designing such flyback power sources is the design of transformers, especially transformers with wide input voltage and multiple outputs.
