1 Introduction

This is a UPS-like circuit with adjustable boost, 1A charging and battery switching circuit, and is suitable for low load situations.

For example, router UPS, power circuit of IoT devices

I have used this kind of circuit in many projects

For example, the ESP32 access control system with the pickup rhythm VU level meter (youth version) that never powers off   is based on ESP12-S and Blinker's temperature and humidity alarm   , but with minor improvements.

2.Principle

The TP4056 chip that charges a lithium battery, and the SX1308 chip that can boost the voltage of the lithium battery.

When the charging port TYPE-C 5V has power, the charging chip will charge the battery, Q1 will cut off at a high level, and the battery current will not flow into the boost chip. Only the D1 diode can use the 5V of TYPE-C to extend the battery life. life.

When TYPE-C does not have 5V, Q2 is turned on at a low level, and the boost chip is powered by the battery.

In addition, the MOS tube here is connected correctly like this, and the reverse is also possible, but a diode must be connected as shown below:

Because the connection as shown above will cause the PMOS to leak to the battery when there is 5V, so a diode must be added, but there will be a voltage difference. If it is placed like in my project, the d level is on the upper side and the s level is on the lower side. The direction of the parasitic diode is The battery boosts the chip, so when there is 5V, there will be no leakage to the battery side, that is, the cutoff is completely cut off.

This method is a hybrid power connection. The connection method in my project is the best.

In addition, this circuit is not suitable for situations where the input voltage is lower than the battery voltage. For example, if the input voltage is 5V, two 7.4V batteries are connected in series, and a boost solution is used for charging. The solution is very simple, just reverse D and S. Remember to add a diode to prevent leakage

Finally, the MOS tube current can flow from S to D, and also from D to S, but the NPN transistor can only flow from c to e, and the PNP transistor can only flow from e to c.

3. Actual measurement

Due to the limitations of the boost chip, it is actually very difficult to output 5V1A, so it is only suitable for low loads. Please check the chip manual for details. The maximum input is 5V and the output is 12V with 800mA.

As shown in the picture above, when there is 5V, the input is only 1.4A. The battery is charged at 1A, but I don’t know how much the charging chip consumes. The specification does not say. If we set 1A for the time being, then the actual boost consumption is only 400mA. Loss is not considered. Therefore, it can only carry a small load in plug-in mode.

However, the load that can be carried in battery mode is much larger than when plugged in 5V, which is the amount written in the boost chip manual.

Boost minimum voltage

The maximum voltage can theoretically reach 30V, but it is limited by the low battery voltage.

Below is a preview of the bugs in the Lichuang preview, as well as schematics and PCBs. You can see them by clicking on them to open them in the editor.