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Buck Circuit Scheme of 220V to 5V Power Supply
Release time:
2022-10-25 09:22
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The step-down circuit of 220V to 5V power supply is widely used in mobile phone charger, switching power supply and so on. The technical solution is generally implemented by performing rectification after step-down of the transformer. Today, I will briefly introduce this technical scheme and another technical scheme using AC/DC voltage reduction. Then, let's learn about the voltage reduction circuit scheme for 220V to 5V power supply!
1. Technical Scheme of Transformer Buck-Rectifier Bridge Rectifier
The key components involved in the technical scheme include step-down transformer, rectifier bridge, filter capacitor, three-terminal voltage regulator, etc. AC 220V is stepped down to 9V after passing through the transformer, and 9V AC is changed into pulsating DC through the rectifier bridge. After filtering, three 7805 are used in this example. Similar chips include LM2596, XL7025 and AMS1117-5V.
2.AC/DC
Integrated chip technology solutions
There are many AC/DC integrated chips. The advantage of using this technical solution is that the volume is very small and the cost is low. But the output current is very small, more for small power household appliances. The output voltage of the chip is adjustable, the FB pin voltage is 1.65V, and the output voltage can be adjusted by adjusting the resistors R1 and R3. In the figure above, the output voltage is 12V, and the rear stage only needs to be reduced to 5V through the triac. The physical diagram of the AC/DC chip is shown in the figure below.
The power supply circuit adopts LM7805 integrated voltage stabilizer as the voltage stabilizing device. In a typical connection mode, the 220V power supply is rectified and filtered and then sent to LM7805 for voltage stabilization. The output terminal is connected with 470U and 0.1U capacitors to further remove ripple and obtain 5V regulated power supply. The loop is shown in Fig. First of all, the high voltage of 220V is transformed, and the specific actual speed ratio of the transformer is determined by the lower circuit. The current after the transformation is still AC, through the rectifier circuit into a pulse DC. The filter circuit can remove the pulse, but the output DC voltage is unstable. The voltage regulator circuit greatly improves the stability of the voltage. The whole process is shown in the figure. The main difference between the two schemes is the voltage stabilizing circuit, and the circuit structure of other parts is basically the same.
220V to 5V power supply positive voltage and negative voltage series regulator integrated circuit small size, high integration, linear adjustment rate and load adjustment rate is high, in the era of linear power supply occupied a larger market. LM7805 is a fixed 5V regulated output integrated circuit (the output of special methods can reach more than 5V), with a large output current of 1A and a standard package format of TO-220 and TO-263. 78 series and 79 series integrated circuit application is relatively fixed, the circuit form is simple. However, when outputting positive and negative DC voltages, it is necessary to pay attention to the small output power and small output voltage of the transformer.
220V to 5V power supply according to the principle of energy conservation, the ideal state of the power supply input and output power is equal. In fact, considering the loss of copper and other components, the output power of the power supply is less than the input power. 78 series and 79 series before and after the DC voltage difference is 2~3V. For positive and negative power output, set the DC voltage difference before and after stabilization to 5~6V
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