I. Selection of overall scheme
According to the design tasks, requirements and conditions, several power supply circuits with certain functions are used as a whole to achieve various performance indicators. The basic steps of this process are: putting forward the scheme, analyzing and comparing, and making a choice. Generally, the basic principle of the scheme can be expressed by block diagram, and the specific circuit can be drawn if necessary. Therefore, it should be noted that:
1. In view of the main problems related to the overall situation of the circuit, several different schemes are put forward, and the reasonable choice is made after in-depth analysis and comparison. 2. The composition of each block diagram should consider the possibility of realization, and the circuits in key and non-absolute blocks need to be designed and experimented to meet the design requirements.
3, the choice of block circuit, since we want to consider digital circuits and analog circuits, we should fully demonstrate different schemes according to specific problems and draw correct conclusions.
4. To choose the best design scheme, we need to constantly improve and perfect it in the process of analysis, demonstration and specific design, in order to achieve the purpose of "reliable performance, low cost and low power consumption", and sometimes there may be some duplication. But we should avoid the big repetition of the plan, so as not to waste manpower and material resources.
Second, the power supply circuit design
In the process of determining the unit circuit, firstly, the requirements for each unit are clearly defined, and the performance indexes of the main unit circuits are drawn up; Secondly, we should pay attention to the mutual cooperation and connection between each unit circuit, so as not to increase the complexity of the circuit; Finally, the structure, component selection and parameter calculation of each power supply circuit are designed respectively. Disadvantages The steps of each unit circuit are: define the requirements, select the sum calculation parameters of the circuit, and consider the following two points again in the process.
1. You can design it yourself or directly refer to the molded unit circuit, but you can't copy it blindly, and make some changes when necessary.
2. Clarify the relationship between each power supply circuit and the whole circuit. Independent unit circuits may sometimes be better if they are considered locally, but they may not be reasonable if they are considered globally. Therefore, we should pay attention to choose the appropriate components from the overall situation and combine the best circuit units.
Third, the choice of components.
In a sense, the design of electronic circuits is to choose the most suitable components, not to combine them best. Therefore, how to choose components is also an important part in the design process. In the process of selecting components, the main issues to be considered are:
1. In the scheme selected according to specific requirements, which components are needed and what functions and performance indicators each component has.
2. Generally, priority should be given to integrated circuits, because the wide application of integrated circuits can simplify the design, facilitate assembly, debugging and maintenance, and at the same time reduce the volume and cost of electronic equipment and improve the reliability of electronic equipment. For integrated circuits, the following points should be made clear:
① Be familiar with the model, performance and price of typical integrated circuit products, so as to choose the appropriate integrated circuit.
② Among the three common packaging methods, namely, dual in-line package, flat package and single in-line package, we should choose according to the principles of assembly, debugging and maintenance.
③ Digital integrated circuits with the same function may have TTL products and CMOS products. When choosing commercial and ECL products, we should master them flexibly according to the respective characteristics, performance and application occasions of circuit design requirements. For example, CMOS devices have low power consumption and wider power supply range than TTL devices.
Fourth, the calculation of component parameters
In the process of electronic circuit design, some parameters need to be calculated to select components. The specific requirements are: using analytical methods, understanding circuit principles and making good use of calculation formulas. When calculating the parameters of components, attention should be paid to:
1, the rated current, voltage, frequency and power consumption of power grid components should be within the allowable range; It can work normally under the specified conditions, and make the circuit meet the requirements of performance standards with appropriate margin.
2. When calculating parameters, environmental temperature, grid voltage and other working conditions should be considered according to the most unfavorable conditions.
For the limit parameters of transistors, such as BVCEO, the power supply voltage should be considered to be about 1.5 times.
On the premise of ensuring circuit performance, the cost, power consumption, volume and types of components are reduced as much as possible, creating convenient conditions for assembly, debugging and maintenance.