The paper introduces the method of making, detecting and managing the DC stabilized power supply in detail. The design of the main circuit, control circuit and simple protection circuit of DC stabilized power supply is introduced first. Secondly, a method for detecting and managing each DC voltage in a complex power system with multiple voltage outputs is proposed, which can improve the efficiency of voltage output detection and realize power management automation. Finally, some specific problems and solutions encountered during the design and test of the power supply are summarized. When the DC stabilized power supply is put into use on the site, its output voltage is stable, its load capacity is strong, its management is convenient and fast, and it meets the design requirements.
Zhang Xingling, Che Jun (Department of Vehicle Engineering, Lanzhou Jiaotong University, Lanzhou 730070, Gansu)
1. Introduction All electronic equipment must work with the support of the power supply circuit. There is a common circuit—the power supply circuit. Based on the characteristics of most electronic components, most electronic devices require power circuits to provide continuous and stable DC power that meets load requirements. Therefore, the design of DC stabilized power supply plays a very important role in the development of electronic products. This thesis mainly introduces the manufacturing method of DC stabilized power supply and the high-efficiency and low-cost detection and management method of DC voltage of various standards in the complex power system of electronic equipment.
2. Production of DC stabilized power supply The design of DC stabilized power supply generally includes four basic links: transformer, rectification, filtering, and voltage stabilization. In order to improve the quality, quality and reliability of the power supply, it is necessary to sample, compare, and amplify the output voltage of the power supply, and use this error amplification signal to adjust its input voltage, so that the output voltage remains stable when the load changes. In addition, in order to improve the safety performance of the power supply, a simple and reliable overvoltage and overcurrent protection circuit needs to be designed to prevent damage to the load components when the voltage and current are too large. The following will briefly introduce the production method of DC stabilized power supply from three aspects, such as the main circuit of the power supply, the control circuit, and the protection circuit design.
A. Main circuit design The main circuit part design mainly includes power transformer, rectifier circuit, filter circuit, voltage regulator circuit design (Figure 1). The transformer changes the high-voltage AC power into the required low-voltage AC power; the rectifier changes the AC power into pulsating DC power; the filter removes the AC components in the DC power; the voltage regulator changes the DC voltage with large fluctuations into a stable DC voltage output (Figure 2 ).
Figure 1 Schematic diagram of the main circuit composition Figure 2 Circuit output waveform diagram The working principle of the transformer is to perform voltage, current, and impedance conversion based on the law of electromagnetic induction. In the design of a DC stabilized power supply, the power transformer generally converts a single-phase power frequency AC 220V voltage into a lower voltage AC power to meet the needs of subsequent circuits. According to the DC voltage and current required by the circuit to determine the number of taps on the secondary side of the power transformer and the voltage and power that each tap should output. In addition, in order to reduce the size and weight of the power transformer, a high-frequency power transformer should be selected.
The use of the unidirectional conductivity of a diode to convert an AC voltage into a unidirectional DC voltage is called rectification. In actual design, a reasonable rectification method should be selected according to the output accuracy and quality characteristics required by the produced power supply.
In the design of a DC stabilized power supply, the AC voltage is generally filtered by using the characteristics that the voltage across the energy storage elements such as inductors and capacitors cannot be abruptly changed, thereby outputting DC voltage with less fluctuation. The DC power output through the filter still contains more AC components, so it cannot be directly applied to both ends of the load, and it needs to be regulated. When the zener tube reversely breaks down, it shows the regulation characteristics within a certain current range, so it can be used to stabilize the DC output voltage. However, its power supply has poor stability and low output accuracy. Therefore, a three-terminal integrated voltage regulator with stable and reliable output is generally selected. It can also shorten the design cycle and reduce the design cost under the premise of meeting the power supply design requirements.
B. Control circuit design Only the above four basic links of the stabilized power supply have poor load capacity. When the load current increases, the output voltage will decrease, which cannot meet the power requirements of most electronic components. Power supply performance is generally improved through closed-loop feedback control and increasing output current.
In order to ensure that the output voltage of the power supply does not change with the change of the load, the power supply itself should be provided with feedback adjustment capabilities. Its principle is shown in Figure 3.
Figure 3 Block diagram of closed-loop regulated power supply When the voltage across the load changes, the sampling voltage of the resistor network changes accordingly. Compare this sampled voltage value with a given reference voltage and amplify this weak error signal Adjust the working state of the control element to adjust the voltage across the load to keep it stable. The control element should be a component with adjustable working status, such as a transistor, whose emitter current will change with the change of the base current. Therefore, by controlling the voltage of the base of the transistor, the conduction degree of the triode can be adjusted, so that Adjust the output voltage of the circuit to meet the requirements.
In addition, in order to improve the load capacity of the power supply, the output current of the power supply can be enlarged by using a transistor. The principle is shown in the following figure.
Figure 4 Current amplification circuit In Figure 4, when the load current is small, the current required by the load is completely provided by the voltage regulator module. As the load current increases, the voltage drop across the resistor R increases, which will cause the series-regulated transistor Q to turn on. The triode together with the voltage regulator module provides the load current.
C. Protection circuit design In order to improve the reliability and safety performance of the power supply, it is usually necessary to design some simple protection circuits, such as overvoltage and overcurrent protection, as shown in the following figure.
Figure 5 System protection circuit In Figure 5, F1, Q1, R5, and R6 form an overvoltage protection circuit. When the voltage across the load increases, the voltage drop across R6 increases, and the thyristor gate triggers current. The thyristor is turned on and instantaneous The large current causes F1 to blow, thus protecting the circuit. R1, Q2, and D1 form a pre-regulation circuit that fixes the input voltage of the voltage stabilization module to a certain voltage value, so that the input voltage does not change with the load. R2, Q3, and R4 form an overcurrent protection circuit. When the current in the circuit is too large, the voltage drop across the resistor R2 increases, causing the transistor Q3 to conduct, thereby providing a path for large currents and preventing the circuit from being damaged by excessive current Element and volt-on element. R3 and Q4 form a current-amplifying circuit to provide the load capacity of the circuit.
3. Power supply voltage detection and management In a complex control system with multiple systems of DC voltage output, when the system fails, first check whether the power output of each chip or circuit is normal, in order to avoid the time consuming caused by manual detection The disadvantages of labor and inconvenience, this paper proposes a simple, reliable, convenient and fast method for detecting the presence or absence of DC voltage output, as shown in Figure 6.
Figure 6: The presence or absence of voltage detection circuits R1 and R2 form a sampling resistor network for the DC output voltage. When the power supply has an output voltage, the voltage drop on R2 makes the optocoupler conductive, and the voltage drop on R5 increases. The high-level signal is sent to the one-chip computer for processing and display. When there is no output voltage from the power supply, there is no voltage drop on R2, and the optocoupler does not work. The voltage on R5 is 0V. This low-level signal is sent to the single-chip microcomputer for display and alarm. Among them, R3 and R4 are current limiting resistors.
This circuit satisfies the condition of voltage detection. On the one hand, the number of components used is small and the price is cheap; on the other hand, the electrical isolation of the main circuit and the control system is realized by the optocoupler, which reduces the interference to the control system. In addition, the real-time monitoring and display of the voltage output of each channel can conveniently check whether the power output is normal or not. This method is suitable for the detection and management of complex power systems with multiple voltage outputs.
4. Problems to be noticed in power supply design The following summarizes some of the problems encountered during the design and debugging of the power supply and their solutions.
Selection of power transformer. In order to reduce the size and weight of the transformer and make it easy to fix on the circuit board, a small and lightweight high frequency power transformer should be selected.
Selection of filter capacitor. On the premise of meeting the volume requirements, try to use electrolytic capacitors with larger capacitance values for filtering. In addition, the capacitor's withstand voltage must not be less than the maximum voltage across its ends.
In the pre-regulation circuit (Figure 5), in order to reduce the power requirement for the current-limiting resistor R1, a transistor Q2 is used to provide a path for current. In practical applications, a transistor with a higher power should be selected for Q2.
In a circuit where a transistor is used for current amplification (Figure 4), the key lies in the debugging of the DC operating point of the transistor, which determines the working state of the transistor and determines the load capacity of the power supply.
In the design and debugging of the entire circuit, the correct calculation of component parameters and the reasonable selection of component types are very important.
If you can fully combine the simulation software to verify the working principle of the circuit during the design process and find out the problems in the circuit in time, you can greatly shorten the design cycle and reduce the design cost. A heat sink should be added to the component that generates heat to prevent the component from overheating.