Other forms of devices that can be converted into electrical energy are called power sources.

Generators can convert mechanical energy and chemical energy into electrical energy, and dry batteries can convert chemical energy into electrical energy.
 
The battery itself is not charged. Its two poles have positive and negative charges respectively. The voltage is generated by the positive and negative charges (current is formed by the directional movement of charges under the action of voltage). Charges are conductive ions widely present in conductors. Only voltage is required to generate current.
 
When the two poles of the battery are connected with conductors, the charge is released in order to generate current. When the charge is exhausted, the dry battery is called power source; the device that converts alternating current into direct current through a transformer and a rectifier is called a rectifier power source. The electronic device that can provide a signal is called a signal source.

Working principle: LED has two requirements for power supply. First, the output voltage is required to be greater than the on-voltage of the LED, and the second is that the working current is stable and cannot be greater than the rated current of the LED. When the working current of the LED exceeds the rated current, the LED will quickly become damaged. Therefore, the power supply used by the LED must have a constant current function.
 
Low-voltage drive Low-voltage drive refers to driving the LED with a voltage lower than the forward voltage drop of the LED, such as an ordinary dry battery or a nickel-chromium/nickel-metal hydride battery, and its normal power supply voltage is 0.8 to 1.65V. Driving an LED with a low voltage requires raising the voltage to a voltage sufficient to turn on the LED. For low-power lighting devices such as LEDs, this is a common use case, such as LED flashlights, LED emergency lights, and energy-saving desk lamps. Due to the limitation of the capacity of a single battery, it generally does not require a lot of power, but requires the lowest cost and relatively high conversion efficiency. In addition, considering the possibility of working with a AA battery and having the smallest volume, the best technical solution is a charge pump boost converter.