What are the working modes of switching power supply?
The working modes of switching power supplies mainly include continuous conduction mode, critical conduction mode, and intermittent conduction mode.
1. Continuous conduction working mode: In this working mode, current always flows through the main switch, and the main switch continues to conduct. This working mode is commonly used for forward and flyback switching power supplies. The advantage is that the output ripple is small and the stability is good. The disadvantage is that it requires a large number of components and has a high cost.
2. Critical conduction working mode: In this working mode, the conduction time of the main switch happens to be at the moment when the output current is zero. This working mode is commonly used for forward and flyback switching power supplies. The advantage is that the number of components is small and the cost is low. The disadvantage is that the output ripple is slightly larger than that of the continuous conduction mode.
3. Intermittent conduction working mode: In this working mode, the conduction time of the main switch is less than the time when the output current is zero. This working mode is typically used for single ended switching power supplies. The advantages are simple design and low cost. The disadvantage is that the output ripple is large and the stability is poor.
To determine which operating mode a switching power supply is in, it can be determined based on the relationship between the conduction time of the main switch and the moment when the output current is zero.
In continuous conduction mode, the conduction time of the main switch is greater than the time when the output current is zero;
In critical conduction mode, the conduction time of the main switch is equal to the moment when the output current is zero;
In intermittent conduction mode, the conduction time of the main switch is less than the time when the output current is zero.
The design and working mode of the magnetic core, which is the main energy storage device in switch mode power supplies, are related. In switch mode power supplies, magnetic cores are mainly used for energy storage and energy transfer. In continuous conduction mode, the magnetic core does not need to completely release the stored energy, so it is not easily saturated; In critical conduction mode, the magnetic core needs to completely release the stored energy, so the saturation problem needs special attention; In intermittent conduction mode, the magnetic core needs to fully release the stored energy in each working cycle, and special attention should be paid to saturation issues.
The critical mode has high requirements for the design of magnetic cores, requiring the selection of appropriate magnetic core materials, cross-sectional area, and number of turns to ensure that the magnetic core does not saturate during operation. Compared with continuous mode, the advantages of critical mode are simple design and low cost; The disadvantage is that the output ripple is relatively large.
Intermittent working mode is not the most commonly used working mode, it is usually used in low-power switching power supplies or special applications. In flyback switching power supplies, the intermittent working mode may be frequently used due to its simple design and low cost
