The universal charger, which I believe is familiar to everyone, is a battery charger that can be used for different spacing and charging various batteries. Its main function is to convert 220V power to store electrical energy into the batteries through voltage reduction.

Universal chargers are not only widely available in the market but also very affordable, with various types such as colorful, alarm, etc., and various appearances. It can be said that after so many years of charger development, the schemes have become very mature.

The circuit is not complicated, mainly consisting of a power management IC. Currently, there are many such ICs available on the market, both domestic and imported, with reasonable costs. Regardless of the IC used, the following points should be noted:

1. Must have automatic detection function
2. Should have feedback and protection capabilities
3. Should have indication function

Here is an example of a popular SE9020 solution found online, which has a certain representative status and is worth sharing with everyone.

Product Features:

1. Automatic Polarity Detection-Conversion (APDC)
2. Full Charge Voltage Accuracy: 4.20V +/- 50mV
3. Automatic Disconnection After Full Charge (ADFC)
4. Battery Fault Automatic Detection (ADBD)
5. Short Circuit Protection (SCP)
6. Overheat Protection (OTP)
7. Maximum Charging Current: 300mA
8. Built-in SE9020 intelligent charging management IC
9. Can maximize the protection of lithium batteries and extend their lifespan

Application Instructions:

Input: USB 5V Output: 4.2V, <300mA Fixed battery: If the red indicator light is on, it indicates good contact between the metal touch point and the battery electrode.

Charging Confirmation: USB=5V, the green indicator light flashes, indicating that it enters the charging state.

Charging Complete: When the green light stops flashing, it indicates that charging is complete. The charger will automatically disconnect the internal electrical connection with the battery.

LED Indicator Explanation:

Red LED: Constantly lit when the battery electrode and metal touch point have good contact. Green LED: Flashes when it enters the charging state; Constantly lit when charging is complete.