The dc charger converts a fixed DC voltage into a variable DC voltage, also known as DC chopper.
There are two working modes of chopper, one is pulse width modulation mode Ts unchanged, changing ton (universal), the other is frequency modulation mode ton unchanged, changing Ts (easy to produce interference).
The circuit through which direct current passes is called DC circuit, which is a closed conductive circuit composed of DC power supply and resistance.
In the DC circuit, a constant electric field is formed.
Outside the power supply, the positive charge flows from the high potential to the low potential through the resistor, and in the power supply, the non-electrostatic force of the power supply overcomes the electrostatic force, and then reaches the high potential from the low potential, which circulates to form a closed current line.
Therefore, in the DC circuit, the function of the power supply is to provide a constant electromotive force that does not change with time to supplement the energy of the Joule heat consumed on the resistance.