Composition of power Supply (1)

A power supply usually contains more than one electromagnetic filter. The first filter is located where the mains is connected to the power supply. It can be found behind the 220v mains interface of a power supply. The main function of the circuit is to filter out the external burst pulse and high-frequency interference, and the other side will reduce the switching power supply itself to the outside electromagnetic interference. Although its structure is simple, mostly composed of X capacitor, Y capacitor and transformer inductance, but it is an important equipment in the power supply, if jerry-built above, the shielding performance of the power supply will be greatly reduced. If we compare the quality brand power supply with the general brand power supply, you will find that most of the brand power supply lacks EMI circuit, the power supply is directly from the mains to the PCB. And this has become one of the core to distinguish the quality of power supply. In addition, many brands of high quality power supply to ensure the purity of the current input to the rectifier circuit, but also designed a second filter circuit. The filter circuit also consists of X capacitor, Y capacitor and transformer-type inductor, located on the PCB near the first EMI circuit.

1.power protector

The varistor is an essential component of every power supply. It is scattered on the PCB to provide protection for the power supply. It works basically like the fuses we have in our homes, using a self-fusing method to cut off the current.

2.Rectifier filter circuit

Ac to DC must pass through a rectifier filter circuit. The most common bridge filter circuit consists of four diodes and two filter capacitors. Computer power is usually rectified in this way. According to different packaging modes, there are two common rectifier filter circuits in computer power supply: one is composed of four independent diodes, and the other is packaged together with four diodes, known as the “full bridge”. There are limits to the minimum voltage and maximum current that can be withstood by both the full bridge and the standalone diode: the voltage should not be less than 700 VOLTS and the maximum current should not be less than 1 ampere.

3.switching voltage and switching triode

In the power supply, transformers of course convert high voltage to low voltage for PC use. According to the principle of electromagnetism, the transformer conversion ratio is mainly determined by the number of turns of the coil, so the larger the size of the switching transformer can often transfer more energy, is also one of the observation points to distinguish high-quality or inferior power supply, to a certain extent, the size of the transformer directly affects the real output power and quality of the power supply. The switching triode is the central hub of the power supply, which is mainly responsible for conveying the converted HVDC to the switching transformer for voltage reduction. Its voltage tolerance shall not be less than 800 VOLTS, and the output current shall not be less than 5 ampere. Switching triode is the core fragile part and the core part of power supply, so the quality of switching triode is closely related to the quality of power supply wood body.

4.protection circuit

The protection circuit inside the power supply monitors the power supply’s every move, which is the power supply’s brain. It is responsible for starting the power supply and voltage/current monitoring and adjustment, at the same time in the occurrence of short circuit, circuit break, overvoltage, overcurrent, undervoltage, undercurrent and other situations when the automatic protection. Inferior power supply will usually simplify this part of the circuit or even do not set the protection circuit, and all this will bring a lot of hidden dangers to the PC system. According to the position of the protection circuit and different types of monitoring, the protection circuit inside the power supply is divided into four types: input overvoltage protection, input overcurrent protection, output overvoltage protection and output overcurrent protection, which is also the origin of the “quadruple protection circuit” advertised by most high quality brand power supply. As the name implies, the overvoltage/overcurrent protection circuit is monitoring the input/output voltage/current when abnormal automatically take effect, so as to achieve protection. In addition, high quality power supply is usually equipped with output short-circuit protection. This is a very useful feature.