A DC power supply is a device that maintains a steady voltage and current in an electrical circuit.
A DC power supply has two electrodes, positive and negative. The positive electrode has a high potential and the negative electrode has a low potential. When the two electrodes are connected to the circuit, a constant potential difference can be maintained between the two ends of the circuit, thereby forming a current from the positive electrode to the negative electrode in the external circuit. DC power supply is an energy conversion device that converts other forms of energy into electrical energy to supply circuits, in order to maintain a stable flow of current.
Relying solely on the difference in water level cannot maintain a stable water flow, but by continuously pumping water from low to high, a certain water level difference can be maintained to form a stable water flow. Similarly, relying solely on the electrostatic field generated by charges cannot maintain a constant current. With the help of a DC power supply, non electrostatic forces (referred to as "non electrostatic forces") can be used to cause positive charges to return from the lower potential negative electrode to the higher potential positive electrode through the power supply, in order to maintain the potential difference between the two electrodes and form a constant current.
The non electrostatic force in a DC power supply is directed from the negative pole to the positive pole. After the DC power supply is connected to the external circuit, a current is formed from the positive pole to the negative pole outside the power supply (external circuit) due to the pushing force of the electric field. Inside the power supply (internal circuit), the effect of non electrostatic forces causes current to flow from the negative pole to the positive pole, thereby forming a closed cycle of charge flow.
An important characteristic of the power source itself is its electromotive force, which is equal to the work done by non electrostatic forces when a unit of positive charge moves from the negative electrode to the positive electrode through the interior of the power source. When the internal resistance of the power supply can be ignored, it can be considered that the electromotive force of the power supply is approximately equal in magnitude to the potential difference or voltage between the two poles of the power supply.
In order to obtain a higher DC voltage, DC power sources are often used in series. At this time, the total electromotive force is the sum of the electromotive forces of each power source, and the total internal resistance is also the sum of the internal resistances of each power source. Due to the increase in internal resistance, it is generally only suitable for circuits with lower required current intensity. In order to achieve a higher current intensity, DC power sources with equal electromotive force can be used in parallel. At this time, the total electromotive force is the electromotive force of a single power source, and the total internal resistance is the parallel value of the internal resistance of each power source.
There are many types of DC power sources, and the nature of non electrostatic forces and the process of energy conversion vary among different types of DC power sources. In chemical batteries (such as dry batteries, rechargeable batteries, etc.), non electrostatic forces are chemical reactions related to the dissolution and deposition of ions. When a chemical battery discharges, chemical energy is converted into electrical energy and Joule heat in thermoelectric power sources (such as metal thermocouples, semiconductor thermocouples). Non electrostatic forces are diffusion effects related to temperature differences and electron concentration differences. When thermoelectric power sources provide power to external circuits, thermal energy is partially converted into electrical energy. In a DC generator, non electrostatic force is caused by electromagnetic induction. When the DC generator is powered, mechanical energy is converted into electrical energy and Joule heat. In photovoltaic cells, non electrostatic forces are the result of the photovoltaic effect. When the photovoltaic cell is powered, light energy is converted into electrical energy and Joule heat.
