Firebeetle Power Supply Explanation

For the power supply issue of FireBeetles, Here we have a basic explanation of the board.

Generally, there are 4 power supply interfaces on Firebeetle, two of them could be used to charge lipo battery, the interfaces are as follow:

From the photo above, pin 1 is Vcc, No.2 is the socket for 3.7V lipo battery, No.3 is the power supply from USB port(can be connected to PC), No. 4 is the interface of external power supply.

The schematic of the power supply part is:

No.1: Vcc can be used to input or output voltage, the voltage value is decided by the input power.
If firebeetle is powered by 3.7V lipo battery, then Vcc would output voltage and the voltage value is 3.7V; 
If firebeetle is powered by USB port, then Vcc has the voltage of 5V as the output; 
When Vcc works as the input, the available voltage is 3.7V~5.5V.

No.2: Powered by 3.7V lipo battery. When the lipo battery and other power supply is connected at the same time, then this interface would work as the charging socket for the lipo battery.

No.3: USB port(corresponding to 5V in the schematic), the port for program uploading, serial debugging, it can only work as a input.

No.4: External power supply interface, input voltage is: 4.5V~5.5V, the external power could be wireless charging module, solar battery panel etc.

From the schematic, there is a power switch chip between the lipo battery interface(VB) and the USB port(5V), when USB is connected, VB can't power Vcc and the circuit, it can only charge the battery, this prevent the current flow back. Besides, in case of Vcc has higher voltage than USB(5V), there is a diode D2 between Vcc and Vin, which means the current can only flow from USB(5V) to Vcc, USB can only work as the power supply. The external power is connected to USB directly, therefore the external power can charge the battery.