As in the question, there is a small system powered by a dc12v adapter. There are three strings of lithium batteries inside. The working current may reach 3~5A. The boost charging circuit is finished, but I want the system to automatically switch to the external power supply when the 12V external power supply is connected. , I don’t know what circuit structure you all use? The more, the better~~ I drew a circuit with IRF power MOSFET, and found that because there is a reverse diode in the MOSFET, it will cause a lot of problems. Unless you add a diode to prevent current backflow, the power consumption of the diode is too wasteful for a 3A current. , Consider whether the reverse withstand voltage of the MOSFET is replaced by a triode. There is no ideal plan yet, please feel free to enlighten me...
In addition, I don’t know if you have used JK flip-flops to make a key switch circuit.
Abbas 发表于 November 4, 2020
Two MOS placed back to back:
Christie 发表于 November 4, 2020
Controlled by a relay, very good.
Rena 发表于 November 4, 2020
First of all, thank you. Single-pole double-throw relays can be switched. If the relay is used in ordinary household circuits, it should be possible, with simple structure and low cost. However, the relay contact time is about milliseconds. During this period, the system is actually without power. If a capacitor is used, a large current system may also require a large volume. Furthermore, if the charging interface is plugged in and unplugged, it will cause frequent contact. Mechanical movement of the head is also inappropriate. Maybe I didn't make it clear that there are modules in this system that are sensitive to power failure protection.
Candy 发表于 November 4, 2020
Continuing the research, tell me the results. Recently, I am studying the original lithium battery protection board.
Rome 发表于 November 4, 2020
Can refer to the design of the S8254 charging IC solution.
