Alone, the difference between the level of water can not maintain a steady flow of water, and by means of continuous water pump from the low to be able to maintain a certain level of water to form a steady flow of water. Similarly, the electrostatic field generated by the charge alone can not maintain a steady current, and by means of a DC power supply, the non-electrostatic effect (referred to as "non-electrostatic force") can be used to make the positive charge from the lower potential Through the internal power back to the higher potential of the positive pole, in order to maintain the potential difference between the two electrodes, resulting in a steady current.
The non-electrostatic force in the DC power supply is directed from the negative pole to the positive electrode. When the DC power supply and external circuit connected to the outside of the power supply (external circuit), due to the electric field force to promote the formation of the positive to negative current. In the power supply (internal circuit), the role of non-electrostatic force is the current from the negative to the positive pole, so that the flow of charge to form a closed loop.
An important feature of the power supply itself is the electromotive force of the power supply, which is equal to the work done by the non-electrostatic force when the positive charge of the unit is moved from the inside of the negative pole to the positive pole. When the power supply to the circuit to provide energy, the supply of power P is equal to the power of the electromotive force E and current I of the product, P = E I. Another characteristic of the power supply is its internal resistance (referred to as internal resistance) R0. When the current through the power supply is I, the thermal power of the internal power loss (ie, Joule heat generated per unit time) is equal to R0I.
When the power supply is positive and negative are not connected, the power is in the open circuit (open circuit) state, then the power between the two electrodes in the value of the value is equal to the power supply electromotive force. In the open state, no non-electrical energy and energy conversion occurs. When the load resistance is connected to the two poles of the power supply to form a closed loop, the current through the internal power flows from the negative pole to the positive pole. At this time, the power supply EI is equal to the power UI delivered to the external circuit The potential difference between the negative electrodes) and the thermal power R0I in the internal resistance, EI = U IR0I. Thus, when the power supply to the load resistance to provide power, the power supply between the two potential difference U = E-R0I.
When the other electromotive force is connected to a smaller electromotive power supply, the positive pole is connected to the positive pole and the negative pole is connected to the negative electrode (for example, the battery is charged with the DC generator). Of the positive current to the negative, this time, the external power input to the power UI, which is equal to the unit time in the power stored in the energy EI and the loss of the heat resistance R0I and UI = E IR0I. Thus, when the outside world to the power input power, the external voltage applied to the two poles should be U = ER0I.
When the internal resistance of the power supply is negligible, it can be assumed that the electromotive force of the power supply is approximately equal to the potential difference or voltage between the two poles of the power supply.
In order to obtain a higher DC voltage, DC power supply will often be used in series, then the total electromotive force for the power of the electromotive force and the total resistance is also the sum of the power supply resistance. Due to increased resistance, generally only for the required current intensity of the smaller circuit. In order to obtain a larger current intensity, the electromotive force can be used in parallel DC power supply, then the total electromotive force is a single power supply electromotive force, the total resistance for the power supply in parallel resistance.
There are many types of DC power supply, different types of DC power supply, the non-static nature of the different energy conversion process is also different. In chemical batteries (such as dry batteries, batteries, etc.), the non-electrostatic force is associated with the dissolution and deposition process of ions associated with the chemical action, chemical cells, chemical energy into energy and Joule heat in the temperature difference (such as metal temperature Even in the semiconductor thermocouple), the non-electrostatic force is a diffusion effect associated with the difference in temperature difference and electron concentration. When the power supply is supplied to the external circuit, the thermal energy is partially converted into electrical energy. In the DC generator, non-electrostatic force is the role of electromagnetic induction, DC generator power supply, mechanical energy into energy and Joule heat. In the photovoltaic cells, non-electrostatic force is the role of photovoltaic effects, photovoltaic power supply, the light energy into energy and Joule heat.