Function

1. Use TP4056 chip to charge 3.7V single-cell lithium battery.
2. Use MST9200BSF to achieve 5V boost for lithium batteries. According to the manual, when the input voltage is greater than 3.3V and the output voltage is 5V, the load current can reach 2A.
3. RT9193-33FB is used to realize the 3.3V step-down output of lithium battery. Unlike AMS1117-3.3V, which can output 800mA current, it can output a maximum current of 300mA, but it is enough to drive microcontrollers and OLEDs.

Introduction to circuit switches

1. SW1 switch is the main switch for lithium battery charging.
2. SW2 DIP switch is a 5V voltage and 3.3V voltage control switch. When not in use, the voltage output can be turned off.

Plug-in introduction

1. There are 4 golden fingers, which can directly weld the pin header in the horizontal direction, or directly weld the wires to other circuits.
2. USB is the charging input port.

Physical circuit diagram

1. Front view (the circuit diagram was drawn incorrectly at the beginning and a jumper was used. Now the open source circuit has corrected the problem)
2. reverse side
3. Charging status (red LED light on)
4. Fully charged (green LED light on)
5. 5V output (the resistors in the circuit diagram are 440k and 60k, PandaJun does not have these resistors on hand, and there is no precise calculation when welding, and a few are roughly welded, so there are errors)
6. 3.3V output

doubt

• What determines the output voltage of a boost circuit?

  The formula used to determine R5 and R6 in this circuit is as follows. See the attachment manual for details.

• Is it possible to charge and output at the same time?

  Yes, this PandaJun has tested it. Theoretically, the charging current is greater than the discharging current, but it is still in the charging state. But it’s best not to charge and output at the same time.

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