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2023-04-25
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A power supply is not like a processor, but its performance can be determined by its specifications; The power supply is not like a graphics card, which is determined by a critical GPU. A good power supply must not only meet power requirements, but also consider various factors such as stability, energy conservation, silence, safety, etc. In the absence of professional equipment for testing, only by understanding the basic principles and component knowledge of the power supply can we achieve a clear understanding of the power supply at a glance.
Seize the key, no longer dizzy
From the outside, the size of the power supply is a bit larger than a "brick", but it actually has a lot of things inside its "belly". Opening the shell, we can see hundreds of various electronic components and complex interlaced cables, which inevitably makes people dizzy. As the saying goes, "Catch the thief first, catch the king." When observing the power supply, we should also pay attention to the following parts.
The internal structure diagram of a certain power supply, numbered 1-6, respectively identifies the parts that everyone should focus on observing.
1. Primary and secondary EMI filtering circuits. The function of this part is to filter the incoming electricity from the external power grid and obtain relatively pure AC power for subsequent use.
2. PFC circuit. Its function is to reduce harmonics during the conversion of AC power to DC power, reduce interference with indoor and municipal power grids, and reduce municipal power losses.
3. High voltage filter capacitor. Its function is to purify high-voltage direct current and provide relatively "pure" current for subsequent high and low voltage conversion.
4. Power topology. Topology refers to the overall structure of a power supply, which directly affects the conversion efficiency of the power supply.
5. Inductive coil of low-voltage filtering circuit. Its function is to stabilize the voltage and current at the output end, which is directly related to the stable use of computer hardware systems.
6. Heat dissipation fins. During voltage conversion between transformers and switching circuits, a large amount of heat is generated, so heat dissipation fins are needed to quickly transfer heat.
Secondary EMI filtering circuit
The national 3C certification requires that listed power supplies must pass EMI anti electromagnetic radiation certification, so qualified power supplies should have EMI filtering circuits.
The first level EMI filtering circuit is located at the power interface, and the circuit with better workmanship also has an independent PCB board and inductance coil.
The secondary EMI filtering circuit is usually located on the main PCB board of the power supply and consists of components such as inductance coils and capacitors.
The secondary EMI filtering circuit on a low-quality power supply sings the song empty city plan
However, low-end power supplies often only have a primary EMI filtering circuit, and slightly better power supplies should have complete primary and secondary EMI filtering circuits.
PFC circuits are divided into two types: passive and active, and most power supplies now use active PFC.
The inductance coil of active PFC is often located in front of the high-voltage filtering capacitor
The power factor of passive PFC is generally around 0.7, while the power factor of active PFC is as high as 0.9 or above, which is significantly better than passive PFC. The distinction between the two is also quite easy.
High voltage filter capacitor
What are high-voltage filter capacitors? Simply put, the highest and largest capacitor in the power supply is (1-2). When comparing capacitors, in principle, it can only be compared with the same type of power supply, because at the same power, the passive PFC power supply requires a larger capacitor capacity than the active one. When comparing at the same level, we can see the capacity, withstand voltage value, and temperature resistance value of the high-voltage filter capacitor. In theory, the larger these three values, the better.
The power supply adopts an active PFC, thus using a capacity of 330 μ The high-voltage filtering capacitor of F can meet the demand. The withstand voltage value of this capacitor is 400V and the temperature resistance value is 85 ℃.Power topology
Simply put, in previous years, the topology of power supplies could be divided into two types: half bridge type and forward type, and now it is mainly forward type. Half bridge type is a traditional power supply structure, usually with low conversion efficiency; And the conversion efficiency of forward structure is easy to achieve over 80%.
Traditional half bridge topology
Forward topology helps improve conversion efficiency
When distinguishing, we may use the exclusion method: in the center of the half bridge power supply, there must be three transformers, one large and two small, arranged in a straight line; If your power supply is not of this structure, congratulations, it is mostly a forward power supply.
