January 14, 2015

# What is a DC power supply ？

A DC power supply is a direct current power supply, which is a device that maintains a stable current in a circuit. Such as dry batteries, storage batteries, DC generators, etc.

The DC power supply has two electrodes, positive and negative. The potential of the positive electrode is high, and the potential of the negative electrode is low. 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 an external circuit from the positive electrode to the negative electrode. negative current.

A constant water flow cannot be maintained solely by the difference in water level, but a constant water level difference can be maintained by means of a water pump to continuously send water from a low place to a high place to form a steady water flow. Similar to this, the electrostatic field generated by the charge alone cannot maintain a constant current, but with the help of a DC power supply, the non-electrostatic effect (referred to as “non-electrostatic force”) can be used to move the positive charge from the negative electrode with a lower potential. Return to the positive electrode with higher potential through the power supply to maintain the potential difference between the two electrodes, thus forming a stable current. Therefore, a DC power supply is an energy conversion device that converts other forms of energy into electrical energy supply circuits to maintain a steady flow of current.

The non-electrostatic force in the DC power supply is directed from the negative pole to the positive pole. When the DC power supply is connected to the external circuit, a current from the positive pole to the negative pole is formed outside the power supply (external circuit) due to the promotion of the electric field force. And inside the power supply (internal circuit), the action of non-electrostatic force makes the current flow from the negative pole to the positive pole, so that the flow of charge forms a closed cycle.

An important characteristic quantity that characterizes 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 unit positive charge moves from the negative pole to the positive pole through the interior of the power supply. When the power supply provides energy to the circuit, the supplied power P is equal to the product of the electromotive force E of the power supply and the current I, P=E I. Another characteristic quantity of the power supply is its internal resistance (abbreviated as internal resistance) R0. When the current passing through the power supply is I, the thermal power lost inside the power supply (ie, the Joule heat generated per unit time) is equal to R0I.

When the positive and negative poles of the power supply are not connected, the power supply is in an open circuit (open circuit) state, and the potential difference between the two electrodes of the power supply is equal to the electromotive force of the power supply in magnitude. In the open circuit state, there is no mutual conversion between non-electric energy and electric energy. When the load resistance is connected to the two poles of the power supply to form a closed loop, the current through the power supply flows from the negative pole to the positive pole. At this time, the power E I provided by the power supply is equal to the power U I delivered to the external circuit (U is the positive pole of the power supply and Potential difference between the negative poles) and the heat power R0I lost in the internal resistance, E I=U I R0I. Therefore, when the power supply provides power to the load resistance, the potential difference between the two poles of the power supply is U=E-R0I. When another power source with a larger electromotive force is connected to a power source with a smaller electromotive force, the positive pole is connected to the positive pole, and the negative pole is connected to the negative pole (for example, a DC generator is used to charge the battery pack), inside the power supply with a small electromotive force, the current is from it At this time, the outside world inputs electric power U I to the power supply, which is equal to the sum of the energy E I stored in the power supply per unit time and the thermal power R0I lost in the internal resistance, U I=E I R0I. Therefore, when the outside world inputs power to the power supply, the voltage applied by the outside world between the two poles of the power supply should be U=E R0I.

When the internal resistance of the power supply is negligible, it can be considered 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 magnitude.

In order to obtain a higher DC voltage, DC power supplies are often used in series. At this time, the total electromotive force is the sum of the electromotive forces of each power supply, and the total internal resistance is also the sum of the internal resistances of each power supply. Due to the increased internal resistance, it can generally only be used in circuits that require a smaller current intensity. In order to obtain a larger current intensity, DC power supplies with equal electromotive force can be used in parallel. At this time, the total electromotive force is the electromotive force of a single power supply, and the total internal resistance is the parallel value of the internal resistance of each power supply.

There are many types of DC power sources. In different types of DC power sources, the nature of the non-electrostatic force is different, and the process of energy conversion is also different. In chemical batteries (such as dry batteries, storage batteries, etc.), non-electrostatic force is a chemical action associated with the dissolution and deposition of ions. When a chemical battery is discharged, chemical energy is converted into electrical energy and Joule heat in a thermoelectric power supply (such as a metal thermoelectric power supply). Couple, semiconductor thermocouple), the non-electrostatic force is the diffusion effect associated with the temperature difference and the concentration difference of electrons. When the thermoelectric power supply provides power to the external circuit, the heat energy is partially converted into electrical energy. In the DC generator, the non-electrostatic force is electromagnetic induction. When the DC generator is powered, the mechanical energy is converted into electrical energy and Joule heat. In photovoltaic cells, the non-electrostatic force is the function of the photovoltaic effect. When the photovoltaic cell is powered, light energy is converted into electrical energy and Joule heat.

Principle of DC power supply

QINXPOWER P series high-frequency switching DC power supply adopts full-bridge phase-shifting pulse width modulation soft switching control technology, which further improves module efficiency and reduces harmonics. The high-frequency switching DC power supply module adopts three-phase three-wire 380VAC balanced input, no phase sequence requirements, no neutral current loss, and advanced peak suppression devices and EMI filter circuits are used at the AC input end. The high-frequency switching DC power supply uses a full-bridge rectifier circuit to rectify the three-phase alternating current into direct current. After passive power factor correction (PFC), the DC/DC high-frequency conversion circuit converts the obtained direct current into a stable and controllable direct current. output. High-frequency switching DC power supply pulse width modulation circuit (PWM) and soft-switching resonant circuit automatically adjust the pulse width and phase shift angle of high-frequency switching according to changes in the power grid and load, so that the output voltage and current can be maintained under any allowable conditions Stablize.

The high-frequency switching power supply can not only work alone to complete various basic functions, but also can work in parallel combination, and has a good effect of parallel current sharing. The high-frequency switching DC power supply can realize the four remote functions of “telemetry, remote signaling, remote control, and remote adjustment” by connecting with a microcomputer. The high-frequency switching DC power supply has complete protection functions to ensure the safety and stability of the independent operation of the module or module group and the system under the monitoring of the microcomputer. The high-frequency switching DC power supply module adopts the bus sampling master and slave current sharing control mode. When running in parallel, a main module can be automatically selected from the high-frequency switching DC power supply module group, and the external parameters such as current and voltage collected by the shunt can be processed to centrally control the output voltage and current of each module. Therefore, even at low current, a better current sharing effect can be obtained.

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