3、tThis project designed an Automatic Switch Device for Double Power Supply which is composed of several parts of the switching and charging circuit, battery voltage monitoring circuit, boost circuit ,buckcircuitand short-circuit protection circuit. The target of the designment is that the de
4、vice can povide voltage of 5V or 12V for external loads under any circumstances.When AC power, it can output the necessary voltage and charge the built-in lithium-ion battery.If there is no po-wer supply, it can switch into a lithium-ion battery to supply power. The dual po-wer supply has
5、strong practicability.This paper mainly describes the procedures to make circuit schematic diagra-ms and printed circuit boards based on the software of Protel 99 SE. The main ac-hievements of this project are as follows.The device has two power supply circu-its, one of which convertes th
6、e AC power into DC power directly ,and the other supply power with two series and two parallel circuits. Apart from this ,the two way circuits both use the relay to switch. The device uses the chip of MAX1873R to supply power for lithium battery, and monitors the status of the lithium batt
7、ery with the chip of TL431. LM2587 rises the output voltage of lithium battery from 7~8.4V to 12V, and LM2596 drops the switched voltage from 12V to 5V. The Relay is used for short circuit protection before it outputs the voltage of 5V and 12V.Keywords：D
