Its working principle is divided into two parts. The first part is a fixed 5V1.5A regulated power supply circuit. The second part is another high-precision, high-current regulator circuit with a continuously adjustable 3 to 15V. The circuit of the first circuit is very simple. The DC voltage rectified by the transformer secondary 8V AC voltage through the silicon bridge QL1 is filtered by the C1 electrolytic capacitor, and then the 5V three-terminal regulator block LM7805 is not used for any adjustment and can be generated at the output. A fixed 5V1A regulated power supply that can be used as an internal power supply when servicing a computer board. The second part is basically the same as the ordinary series-type regulated power supply. The difference is that the high-precision standard voltage source integrated circuit TL431 with temperature compensation characteristics is used, so the circuit is simplified, the cost is reduced, and the voltage regulation performance is high. . In the figure, the resistor R4, the voltage regulator TL431, and the potentiometer R3 form a continuously adjustable constant voltage source, which provides a reference voltage for the BG2 base. The voltage regulation value of the voltage regulator TL431 is continuously adjustable, and this regulation value determines the stability. The maximum output voltage of the voltage source. If you want to expand the adjustable voltage range, you can change the resistance of R4 and R3. Of course, the secondary voltage of the transformer also needs to be increased. The power of the transformer can be flexibly controlled according to the output current, and the secondary voltage is about 15V. The rectifier tube QL for bridge rectification uses a 15-20A silicon bridge. It has a compact structure and a fixing screw in the middle. It can be directly fixed to the aluminum plate of the casing to facilitate heat dissipation. The adjustment tube uses a high-current NPN-type metal-shell silicon tube. Because of its large heat generation, if the chassis allows, try to buy a large heat sink to expand the heat-dissipation area. If you do not need a large current, you can also use a smaller power. Silicon tube, which can be made smaller. Filtering 50V4700uF electrolytic capacitors C5 and C7 are connected in parallel with three, so that the large current output is more stable. In addition, this capacitor should be purchased in a relatively large volume. Those smaller in size are also marked with 50V4700uF as much as possible. When encountering frequent voltage fluctuations, or Not used for a long time, it is easy to fail. Finally, let's talk about the power transformer. If you don't have the ability to wrap it yourself, you can't buy a ready-made one. You can buy a ready-made switching power supply of more than 200W instead of the transformer. This can further improve the voltage regulation performance, but the production cost is not too bad. Other electronic components have no special requirements, and they can work normally without much adjustment after installation.
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