DC power supply has positive and negative two electrodes, anode potential, anode potential is low, when the two electrodes and the circuit connected, to maintain a constant potential difference between the two ends of the circuit, thus forming the anode current to the anode in the external circuit. Rely on the water level difference can not maintain steady flow, and with the help of the pump continuously the water from low to high to maintain a certain water level difference and the formation of steady flow. Similarly, by electrostatic field cannot charge generated by the current maintained steady, and with the help of the DC power supply, you can use the non electrostatic interaction (referred to as "non static electricity") the positive charge at the cathode by the low potential return to the anode potential is higher by the power source to maintain the potential the difference between the two electrodes, thereby forming a steady current. Therefore, the DC power supply is an energy conversion device, which converts other forms of energy into electrical energy supply circuit to maintain the steady flow of current.
The non electrostatic force in the DC power supply is from the negative electrode to the positive electrode. When the DC power supply is connected with the external circuit, a current from the positive electrode to the negative electrode is formed on the external side of the power supply. In the power supply (internal circuit), the role of non static electricity so that the current from the negative electrode to the positive electrode, so that the flow of charge to form a closed cycle.
An important characteristic of the performance of the power supply is the electromotive force of the power supply, which is equal to the work done by the electrostatic force when the positive charge of the unit moves from the negative electrode 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 product, P=E I. Another feature of power is its internal resistance (the resistance) R0, when the power supply current of I, thermal power internal loss (Joule heat generated per unit of time) is equal to R0I.
When the positive and negative poles of the power supply are not connected, the power supply is in a state of open circuit (open circuit), and the potential difference between the two electrodes of the power supply is equal to the electromotive force of the power supply. In the case of open circuit, no conversion of non electric energy and electric energy. When the load resistance power poles to form a closed loop, the flow from the cathode to the anode, current through the internal power supply of the power E provided by I U is equal to the power delivered to the external circuit I (U is the power supply potential between anode and cathode loss difference) and internal resistance of thermal power R0I and E I=U IR0I. Thus, when the power supply to the load resistance power supply, the potential difference between the two power supply U=E-R0I.