"Clear at a glance" inside power supply
The power supply does not look like a processor, you can see specifications and performance; power supply is not like a video card, class is determined by key GPU.
In addition to power requirements, a good power supply must also consider many factors such as stability, power saving, quietness, and security.
In absence of professional testing equipment, we can only "clean" power supply if we understand some of basic principles and components of power supply.
Take key, no more dizziness
From side, power supply looks more like a “brick”, but there is quite a lot of things in its “belly”.
Dissecting case, we see hundreds of different electronic components and complex intertwined cables that inevitably make people dizzy. As saying goes, "Catch thief first, catch king first."
In diagram of internal structure of a specific power supply, serial numbers 1 to 6 respectively indicate parts that should be paid attention to.
First and second EMI filter circuits. The function of this part is to filter mains electricity coming from off-site power grid to produce relatively clean AC power for later use.
PFC outline. Its function is to reduce harmonics in process of converting AC to DC, reduce interference of internal power grid and power grid, and reduce power losses in network.
High Voltage Filter Capacitor. Its function is to clean up high voltage DC and provide a relatively "clean" current for subsequent high and low voltage conversion.
Power topology. Topology refers to overall structure of power supply, which directly affects conversion efficiency of power supply.
Low voltage filter circuit inductor. Its function is to stabilize voltage and current of output terminal, which is directly related to stable use of computer hardware system.
Radiator. When transformers and switching circuits perform voltage conversion, a large amount of heat is generated, so heat sinks are required to quickly transfer heat.
1. EMI filter primary and secondary circuits
National 3C certification requires listed power supplies to pass EMI certification, so corresponding power supplies must have EMI filter circuits.
The primary EMI filter circuit is located on power interface, and circuit with better workmanship also has an independent circuit board and inductor.
The secondary circuit of EMI filter is usually located on main circuit board of power supply and consists of components such as inductors and capacitors.
The secondary EMI filter circuit in a low quality PSU sings "blank city plan", but a budget PSU often only has a primary EMI filter circuit, and a slightly better PSU should have a complete primary and secondary EMI filter circuit.
2. PFC Schema
Power factor correction circuits are divided into two types: passive and active, and currently most power supplies use active power factor correction.
All passive PFCs use this large head inductor.
The inductor of an active PFC is often located in front of high voltage filter capacitor. The power factor of passive PFC is typically around 0.7, while power factor of active PFC reaches 0.9 or more, which is clearly better than passive PFC. It's also pretty easy to tell difference between two.
3. High Voltage Filter Capacitor
What are high voltage filter capacitors? Very simple: tallest and largest capacitors in power supply (1 to 2 capacitors). When comparing capacity, in principle, it can only be compared with same type of power supply, because. at same power, capacity required by passive PFC power supply is greater than that of active one. When compared at same level, we can see capacitance, withstand voltage value, and thermal resistance value of high-voltage filter capacitor. In theory, larger value of these three items, better.
The power supply uses active power factor correction, so 330uF high voltage filter capacitor can meet demand. The voltage resistance value of this capacitor is 400V and temperature resistance value is 85°C.
4. Power Topology
To put it simply, in past few years, power supply topology can be divided into two types: half-bridge type and direct type, and now direct type is mainly mainstream type. The half-bridge type is a traditional power supply structure, and conversion efficiency is generally not high, while direct structure conversion efficiency can easily reach more than 80%.
Traditional half-bridge topology
Direct topology helps to improve conversion efficiency. When making distinction, we could also use elimination method: in center of half-bridge of power supply, there should be three transformers, one large and two small, arranged in a straight line, if your power supply is not of this design, then congratulations, most likely it is a direct power supply.
5. Low Voltage Filter Circuit Inductor
In low voltage filter circuit part, we are mainly looking at size, number of turns, and color of inductor coil. Naturally, larger coil and more turns, better, as far as color is concerned, then theoretically they are gray, black, light green and yellow from good to bad, and better inductance, less loss.
The circuit part of low-voltage filter is mainly dependent on inductor
Needless to say about role of heatsink, switching tube and Schottky tube with high heat dissipation are often installed on heatsink.
Commercially available PSUs currently use aluminum heatsinks, usually thicker better; at same time, in order to expand heat dissipation area in a limited space, most heat sinks are theoretically equipped with fins, more fins, better.
- What is drowning in gold? Why Shen Jin?
- This is a metaphor for EMI/EMS/EMC that can be understood at a glance.
- How many types of pads have you seen in PCB design?
- Summary of Common PCB Repair Techniques
- What is three anti-paint? How to use it correctly?
- Knowing these rules, you will not get confused looking at circuit diagram.
- How to make anti-interference PCB design?
- Can diodes do this?