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Switching power supplies are widely used in manufacturing and life, and are a key component of electronic product design. The switching power supply is small, light and efficient, but do you really have to master the switching power supply? This article will explain the meaning of switching power supply and the principle of switching power supply in detail to help you better master switching power supply.
First, what is a switching power supply.
Switching power supply is the use of switching element components (such as electron tubes, field effect transistors, thyristor thyristors, etc.), according to the control loop, the switching element components are continuously connected and turned off.
The switching power supply is relative to the linear power supply. His plug-in terminal immediately converts the AC rectifier into a DC power supply, and then, under the effect of a high-frequency resonant circuit, uses a power switch to manipulate the conduction of the AC power to generate a high-frequency surge current. With the help of an inductor (transformer coil), a smooth low-voltage DC power supply is output. Because the core specification of the transformer is inversely proportional to the square meter of the output power, the higher the frequency, the smaller the transformer core. This can greatly reduce the transformer and ease the overall weight and volume of the power supply. And, because it immediately manipulates DC, this type of power supply is far more efficient than linear power supplies. This saves electrical energy and is therefore very popular with us. But it is also flawed. The switching power supply circuit is complicated, maintenance is difficult, and the environmental pollution of the power supply circuit is relatively serious. The power supply is noisy, and it is uncomfortable to use some low-noise power supply circuits.
The linear power supply first reduces the amplitude of the AC voltage according to the transformer, then obtains a single-pulse DC power supply according to the bridge rectifier circuit rectifier, and then obtains a DC voltage containing a small ripple voltage according to filtering. In order to better achieve a high-precision DC voltage, it is necessary to develop a Zener tube according to the regulated power supply circuit.
Second, the principle of switching power supply.
The whole process of the operation of the switching power supply is relatively easy to understand. In a linear power supply, make the output power tube network work. Unlike linear power supplies, PWM switching power supplies keep the output power tubes on and off. In the two cases here, the volt-ampere multiplication added on the output power tube is very small (the voltage is low and the current is large when it is turned off; the voltage is high and the current is small when it is turned off) / volt-ampere on the power electronic device The multiplication of the characteristic curves is a damage on the output power semiconductor components.
Compared with the linear power supply, the more reasonable operation link of the PWM switching power supply is completed according to the inverter, and the DC voltage to be input is cut into a single pulse voltage whose amplitude value is equivalent to the input voltage amplitude value.
Third, the advantages and disadvantages of switching power supply:
The specific advantages of switching power supply: small size, light weight (volume and total weight are only 20~30% of linear power supply), high efficiency (generally 60~70%, while linear power supply is only 30~40%), anti- Strong interference ability, wide output voltage coverage, modular design.
The specific defects of the switching power supply: because the rectifier circuit causes high-frequency voltage, it has a certain impact on the surrounding facilities. Good shielding and grounding must be maintained.
The AC current can pass through the rectifier to get the DC power. As everyone knows, due to the change of the AC voltage and the load current, the DC voltage obtained after the rectifier usually causes a voltage change of 20% to 40%. In order to get a better stable DC voltage, be sure to use a regulated power supply circuit to complete the zener tube. According to the different completion methods, the voltage regulator tube power supply can be divided into three types: linear voltage regulator tube power supply, phase-controlled voltage regulator power supply and switching regulator tube power supply. Switching power supply means the development trend of green environmental protection and excellent power supply.
Fourth, the common problems when choosing a switching power supply.
(1) Select the appropriate input voltage specification model;
(2) Select the appropriate output power. In order to better increase the life of the power supply, you can choose a model with a rated power exceeding 30%.
(3) Taking into account the load characteristics. If the load is a motor, light bulb or capacitor load, and the current is relatively large during operation, an appropriate power supply should be selected to prevent the load. If the load is a motor, the voltage reversal at shutdown should be considered.
(4) In addition, the operating temperature of the power supply and whether it has excess auxiliary cooling equipment should also be considered. Excessive temperature sensing power supply must reduce the output. Temperature reduction power curve.
(5) Various functions must be selected according to the use:
Maintenance functions: Over Voltage Protection (OVP), Temperature Protection (OTP), Over Voltage Protection (OLP), etc.
Application functions: data signal function (normal power distribution, invalid power distribution), remote control function, monitoring function, parallel connection function, etc.
Unique Features: Power Factor Correction (PFC), Continuous Power (UPS)
Select the required security requirements and EMC performance (EMC) verification.