Based on LP2951 lithium-ion battery charger circuit

Stable National Semiconductor LP2951 manufacturing. Article "Charging" by Chester Simpson, taken from Elemental Values.

Diode D1 can be purchased from any of the 1N400X series series. It is used as a lock to prevent reverse current from the battery chip LP2951 when the input voltage is disconnected.

The charging current is about 100 mA, and the maximum current of this value is limited by the internal circuit chip LP2951 . For those interested, let us explain that any lithium-ion battery can be charged with a charging current of 1C (i.e. the current capacity is equivalent to milliamps, so for example, a battery capacity of 1100 mA can be charged up to 1100 mA). Lower charging current leads, respectively, to more charging time. In my humble opinion, 100 mA - a relatively low charging current that allows a typical Li-ion battery to be connected to this charger at night.

The resistors are specifically chosen to be high order (tens/hundreds of ohms and megawatt range) so that the current through them at the supply input voltage has to be as low as possible about 2 microamps. In order to ensure good accuracy of the output voltage resistor, the tolerance must be within 1%. The output voltage of the potentiometer 50 ohm ranges between 8.4 V and 4.26 V. This makes it different depending on the type of rechargeable battery, and its value is set to 4.1 or 4.2 V. The capacitors, especially C2, are needed to ensure the sustainability of the program sex.