Basic components of 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
DC: Switching power supplies output DC instead of AC, and can also output high-frequency AC, such as electronic transformers
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.
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.
Rectifier filter circuit
The AC voltage is rectified by BRG1 and filtered by C5 to obtain a relatively pure DC voltage. If the capacity of C5 decreases, the output AC ripple will increase, so choosing a suitable C5 is very important for system stability.
Experience selection: Generally, 380VAC switching power supply C5 without PFC is selected based on 1.5-2.5uF/w. According to this standard, the vast majority of power filtering requirements can be met. The specific difference should be based on the ambient temperature, and the capacitance should be larger when the temperature is high.
Capacitor C6 is a high-frequency thin film capacitor that provides energy and circuit during rectifier bridge commutation, and has a significant inhibitory effect on power conduction interference.
