Composition
The circuit diagram is mainly composed of component symbols, connections, nodes, and comments. The component symbol indicates the component in the actual circuit, and its shape is not necessarily similar to the actual component, or even completely different. But it generally shows the characteristics of the component, and the number of pins is consistent with the actual component. The wire means the wire in the actual circuit. Although it is a wire in the schematic diagram, it is often not a wire but a copper foil block of various shapes in a commonly used printed circuit board, just like many in the radio schematic diagram. The wiring in the printed circuit board diagram is not necessarily all linear, but may also be a copper film of a certain shape. The node represents the connection relationship between several component pins or several wires. All component pins and wires connected to the node, regardless of the number, are conductive. Notes are very important in circuit diagrams, and all text in circuit diagrams can be classified into the comment-type. If you look closely at the above diagrams, you will find that there are notes in various places in the circuit diagram, which are used to illustrate the model, name, etc. of the component.
Classification
Circuit diagrams include schematic diagrams, block diagrams, assembly diagrams, printed board diagrams, etc.
Schematic diagram
Also called "electrical schematic diagram". This kind of diagram, because it directly embodies the structure and working principle of the electronic circuit, is generally used in the design and analysis of the circuit. When analyzing the circuit, by identifying the various circuit component symbols drawn on the drawing and the connection between them, you can understand the actual working principle of the circuit. The schematic diagram is a tool used to reflect the working principle of the electronic circuit. .
Block diagram
Abbreviated as the block diagram, the block diagram is a circuit diagram that uses blocks and connections to show the working principle and composition of the circuit. Fundamentally speaking, this is also a kind of schematic diagram, but in this kind of drawing, there are almost no other symbols except for boxes and lines. The main difference between it and the above schematic diagram is that all the components of the circuit and their connection methods are drawn in detail on the schematic diagram, while the block diagram simply divides the circuit into several parts according to the function, and depicts each part. To form a box, add a simple text description in the box, and use a line between the boxes (sometimes use a line with arrows) to illustrate the relationship between the boxes. Therefore, the block diagram can only be used to reflect the general working principle of the circuit, and the schematic diagram can be used as a basis for collecting components and making circuits in addition to showing the working principle of the circuit in detail.
Assembly drawing
It is a kind of drawing used for circuit assembly. The symbols on the drawing are often the physical appearance drawings of circuit components. As long as we follow the picture on the picture and connect some circuit components in the same way, we can complete the circuit assembly. This kind of circuit diagram is generally for beginners to use. The assembly drawings are different according to the different assembly templates. In most cases where electronic products are used, the printed circuit boards described below are used, so printed board drawings are the main form of assembly drawings. When learning electronic knowledge, in order to be able to get in touch with electronic technology earlier, we chose the screw hole plate as the basic installation template, so the installation drawing becomes another mode.
Printed board drawing
The full name of the printed board drawing is "printed circuit board drawing" or "printed circuit board drawing". It is actually the same type of circuit diagram as the assembly drawing. It is used for assembling the actual circuit. The printed circuit board is covered with a layer of metal foil on an insulating board, and then the metal foil that is not needed by the circuit is corroded. The remaining part of the metal foil is used as the connection line between the circuit components, and then the components in the circuit The device is mounted on this insulating board, and the remaining metal foil on the board is used as a conductive connection between the components to complete the circuit connection. Because the metal covered on one or both sides of this circuit board is copper, the printed circuit board is also called "copper clad laminate." The component distribution of the printed board diagram is often quite different from the schematic diagram. This is mainly because, in the design of the printed circuit board, the main consideration is whether the distribution and connection of all components are reasonable. It is necessary to consider many factors such as component volume, heat dissipation, anti-interference, anti-coupling, etc., and the printed circuit board designed by combining these factors From the outside, it is difficult to be completely consistent with the schematic; in fact, it can better realize the function of the circuit. With the development of science and technology, the manufacturing technology of printed circuit boards has been greatly developed; in addition to single-panel and double-panel, there are also multi-panel, which has been widely used in daily life, industrial production, national defense construction, aerospace industry, etc. Field. In the four forms of circuit diagrams introduced above, the electrical schematic diagram is the most commonly used and the most important. If you can understand the schematic diagram, you can basically master the principle of the circuit. Draw block diagrams, design assembly diagrams, and printed board diagrams. It's easy. It is also very convenient to master the schematic diagram to repair and design electrical appliances. Therefore, the key is to master the schematic diagram.
Drawing rules
PROTEL, Protel DXP, Pads, Pcad, Orcad, powerlogic, allegro, Mentor, powerpcb, AutoCAD, CAXA, etc.
Current=Voltage /Resistance letter expression is I=U/R (Ohm's law) deformation: R=U/IU=IR
Resistance=voltage/current
Circuit diagram examples (5 photos)
The drawing rules of the circuit diagram: 1. The signal processing flow direction of the circuit diagram; 2. The connection wire; 3. The method and steps of identifying the power line and the ground circuit diagram.Circuit identification includes the judgment of correct circuit and wrong circuit, the judgment of series circuit and parallel circuit. The faulty circuit includes the lack of necessary components in the circuit (the necessary components include power supply, electrical appliances, switches, and wires), the inability to form a current path, and the circuit is open or short-circuited. The current flow method is usually used to determine the connection of the circuit. If the current passes through each consumer in sequence without shunting, the consumer is connected in series; if the current passes through the consumer before and after the branch, that is, the current passing through each consumer is part of the total current, then these consumer The electrical appliances are connected in parallel. When judging the circuit connection, there is usually a situation where a wire is used to connect two points of the circuit. In the junior high school stage, the resistance of the wire can be ignored, so the two points connected by a wire can be regarded as one point, so sometimes it is used The "node" method is very convenient to judge the connection of the circuit.
Starting from the power supply, mark an A on the positive pole of the power supply and a B on the negative pole. Then start from the positive pole and walk along the wire. When you encounter the first electrical appliance, mark the end of the wire extending from the positive pole with an A, and mark the other end with a C (because the negative pole is marked with B). , So change a letter, but if the other end of the electrical appliance is directly connected to the negative pole, follow the above-mentioned method to mark B starting from the negative pole) After marking C, continue to go, if you encounter the next one Change the electrical appliances again...Remember, the premise of changing to another letter is that the end is not connected to the negative wire. In this way, after you finish marking the letters, if all the electrical appliances have different letters on both sides, the entire circuit is connected in series; if there are several electrical appliances with the same letters on both sides, then these electrical appliances are connected in parallel.
The physical connection diagram is connected according to the circuit diagram you have drawn, and be careful not to connect the lines.
The method of circuit connection is as follows: 1. Before connecting the circuit, first draw the circuit diagram. 2. Place the circuit components according to the corresponding positions in the circuit diagram. 3. The connection of the circuit should be carried out in a certain order. 4. When connecting parallel circuits, you can proceed in the order of "dry first, then branch", that is, connect the main circuit first, then connect each branch, and then parallel each branch to the two ends of the circuit, or press The sequence of "support first, then work" is connected. Pay attention to the following points when connecting the circuit: 1. During the circuit connection, the switch should be disconnected. 2. Every connection must be connected firmly to prevent virtual connection. 3. First connect electrical appliances, switches and other components, and finally connect to the power supply. 4. Check carefully after connection, and then close the switch after confirming that it is correct. 5. After closing the switch, if an abnormal situation occurs, immediately disconnect the circuit, check carefully, and eliminate the fault.
Attention
1. The components should be distributed evenly, and don't draw on the corners.
2. The whole circuit is best to be rectangular, and the wires should be horizontal and vertical, with edges and corners.
3. According to a certain order, if there are letters, mark the corresponding letters.
Unit circuit
Recognition
Unit circuit refers to a certain level of controller circuit, or a certain level of amplifier circuit, or a certain oscillator circuit, Inverter circuit, etc., it is the smallest circuit unit that can complete a certain circuit function. In a broad sense, the application circuit of an integrated circuit is also a unit circuit.
The circuit diagram of the unit is the first to encounter a circuit diagram with complete functions in the process of learning the working principle of the electronic circuit of the whole machine. The concept of this circuit diagram is put forward to facilitate the analysis of the working principle of the circuit.
Function
The circuit diagram of the unit has the following functions:
①The circuit diagram of the unit is mainly used to describe the working principle of the circuit.
②It can completely express the structure and working principle of a certain level of circuit, and sometimes all the parameters of each component in the circuit are marked, such as nominal resistance, nominal capacity and transistor model.
③It is very helpful to deeply understand the working principle of the circuit and the structure and composition of the memory circuit.
Features
The circuit diagram of the unit has the following characteristics:
①The circuit diagram of the unit is mainly used to analyze the working principle of a unit circuit and separate this part of the circuit. For the circuit drawn, other components and related connections and symbols that have nothing to do with the unit circuit have been omitted in the figure, so that the unit circuit diagram appears relatively simple and clear, and there is no interference from other circuits when recognizing the diagram. The unit circuit diagram has simplified the power supply, input end and output end, as shown in Figure 1-6. Source: Power Transmission and Distribution Equipment Network
In the circuit diagram, +V is used to represent the DC working voltage (where the positive sign indicates that the positive polarity DC voltage is used to power the circuit, and the ground terminal is connected to the negative electrode of the power supply); Vi indicates the input signal , Is the signal to be amplified or processed by this unit circuit; VO represents the output signal, which is the signal after this unit circuit is amplified or processed. The power supply terminal, input terminal and output terminal can be easily found through the label in the unit circuit diagram. In the actual circuit, the circuits of these three terminals are all connected to other circuits in the complete circuit without +V, Vi, The labeling of VO makes it difficult for beginners to read pictures.
For example: when you see Vi, you can know that the signal is added to the base of transistor VT1 through capacitor C2; when you see VO, you can know that the signal is output from the collector of transistor VT1, which is equivalent to marking in the circuit diagram The input and output of the amplifier undoubtedly greatly facilitate the analysis of the working principle of the circuit.
②The unit circuit diagram adopts the customary drawing method, which can be understood at a glance. For example, the components adopt the customary drawing method, and the shortest connection between each component is adopted. However, in the actual circuit diagram of the whole machine, due to The constraints of the components in the other unit circuits in the circuit. The related components are drawn in a mess, some are not common in the painting method, and some individual components are drawn far away from the unit circuit, so that the components in the circuit The connection is very long and twists and turns, causing inconvenience in understanding the diagram and the working principle of the circuit.
③The circuit diagram of the unit only appears in books and magazines explaining the working principle of the circuit, and it does not appear in the practical circuit diagram. The study of unit circuits is the key to learning the working principles of electronic circuits. Only by mastering the working principle of the unit circuit can the whole circuit be analyzed.
Operation process
Physical connection diagram
1. If it is a series circuit, connect it from the positive pole of the power supply to the negative pole of the power supply in a certain order. Whatever is connected until it is completed;
2, if it is a parallel circuit, you can take the method of branching to complete-divide the circuit into several paths, and then complete the connection one by one;
< p>3. It should be noted:a. The wire must be connected to the two terminals of the component,
b. It cannot form a cross wire and must be connected by a detour
C. Connect the physical diagram strictly in accordance with the order of the components in the circuit diagram.
Draw the corresponding circuit diagram
1. If it is a series circuit, draw from the positive pole of the power supply to the negative pole of the power supply in a certain order, and draw whatever you encounter until it is completed;
2. If it is a parallel circuit, you can take the method of dividing the circuit into several paths, and then complete the connection one by one; if it is a parallel circuit, pay attention to the points that intersect and connect. Use obvious black dots to trace.
3. Things to pay attention to when drawing a circuit diagram:
A must use circuit symbols to represent components, not physical graphics
B The entire circuit drawing is a box Type
C Draw the circuit diagram according to the order of the components in the physical picture
D Develop a good habit of using letters to indicate each component at any time
E Be careful not to connect To form an open circuit, the node should be good!
Introduction to commonly used circuit design software
With the gradual popularization of computers in China, the application of EDA (Electronic Design Automatic, circuit design automation) software in the circuit industry has become more and more extensive. These software include circuit design and simulation tools, PCB design software, IC design software, PLD design tools and other EDA software. Here we mainly introduce the schematic and PCB diagram design tools. Of course, a lot of EDA software already covers all functions and even more functions.
Design software
From Protel to Altium
As long as you are engaged in electronics, you know PROTEL, just like using a computer Just know the WINDOWS operating system, this is because many of its operating habits have been rooted in the hearts of cyborgs. PROTEL is a CAD software for the circuit industry launched by PORTEL (now Altium) in the late 1980s. It deserves to be ranked in front of many EDA software and is the software of choice for circuit designers. It was used earlier in the country and has the highest penetration rate. It is used by almost all circuit companies.
From the original PCB design tool in the DOS environment to the powerful AltiumDesigner, Altium has launched many different versions. As far as I know, the most used versions are as follows:
p>PROTEL99SE: Although it is a very early version, many companies are still using it, and we are using it. Some companies even only recognize this version of the file. Almost 10 years have passed, comrades, know the power of habit!
PROTEL2004SP4: In 2002, Altium released PRTELDXP. In addition to some enthusiasts who started to try it early, some people still hold PROTEL99SE and refuse to release it. Some people even now. But after all, there are still many new features that attract new users. When they have to change the version, many people may directly use the latest version of PROTEL2004 at that time. The version after the addition is no longer named after PROTEL. This version is regarded as a PRETEL commemorative work. When opening new types of files that PROTEL99SE cannot open, this second stage classic version is used.
AltiumDesigner6.8: In 2005, Altium officially released AltiumDesigner6.0. Since then, the era of PROTEL is over. It was not until 2007 that AltiumDesigner 6.8 was released, which is the latest version. I believe that many people haven't used it, but many people should try it first. It is said that the software integrates all the technologies and functions required for the integrated development of electronic products. Provides a unified application for electronic engineers and designers. Including board system design, FPGA-level system design, FPGA and discrete processor-based embedded software development, PCB layout, editing and manufacturing. And integrated into the modern design data management function. Tools such as P-CAD released before are gradually integrated into AltiumDesigner after 2006. But I don't particularly agree with this approach. Circuit design mainly uses schematic and PCB design. The other miscellaneous functions are also upset. And after all, there are more professional tools OrCAD and CADENCE
OrCAD and CADENCE
ORCAD is an EDA software launched by ORCAD in the late 1980s . Many people are not unfamiliar with it. It is known as the best tool for drawing circuit schematics. However, because the software uses a softdog to prevent piracy, it is not popular in China, and its popularity is not as good as PROTEL.
Similarly, there is also a PCB tool that is said to be the best to use, that is CADENCE's Allegro, I have used it, and I think it is indeed easy to use.
However, there is better news, that is, CADENCE acquired ORCAD later, which is a strong alliance. Later, ORCAD and ALLEGO can also carry out interactive design. For users, this is nothing more than a good thing. Therefore, many people use ORCAD (later called DesignEntryCIS) for schematic design and ALLEGO for PCB layout design, to be the best partner. Many textbooks are introduced in this way.
Of course, ORCAD and ALLEGO are not brothers after all. Whether they can be the best partners, there may be a break-in period. Moreover, ORCAD also has the original brother PCB tool ORCADLAYOUT. ALLEGO also has the original brother schematic design tool DesignEntryHDL. Some people even use ORCAD to draw schematics, and after generating a netlist, they use PRETEL to draw PCBs. In order to take into account the usage habits of many people, CADENCE company still integrates all the tools (when the PRETEL is not included) into an integrated environment. Users can use whichever they want. As far as I am concerned, I still feel that ORCAD and ALLEGO can be the best partners. But now, whether our company or many big companies use DesignEntryHDL and ALLEGO, perhaps because they also have a dedicated project manager, which is better connected with other simulation tools and more interactive. Well, maybe it's because they are brothers... But when I started to learn DesignEntryHDL, I felt that it was really not in line with my habits. Maybe it was PROTEL's operating habits that were preconceived, but DesignEntryCIS gave me a very good feeling, although I didn't use it much. Over. Fortunately, after learning DesignEntryHDL, I gradually got used to that kind of operating habits.
To this day, CADENCE refers to these tools as the CadenceAllegro system interconnection design platform, which mainly include: DesignEntryCIS (ORCAD) schematic design tool, DesignEntryHDL schematic design tool, AllegroPCBEditor printed circuit board Design tools (ALLEGRO referred to above), AllegroAMSSimulator simulation tools, AllegroPCBSI signal integrity analysis tools, etc. What’s more worth mentioning is that CADENCE is better at high-speed signal simulation. As we all know, as the signal frequency of the circuit board card becomes higher and higher, the size becomes smaller and smaller, etc., the circuit board is not all connected. It can work normally if it is correct. Therefore, signal integrity analysis becomes more and more necessary. CADENCE provides many such tools, such as the constraint manager in PCBEditor, etc., which can help users consider signal integrity to a large extent. For the version I use AllegroSPB15.2, but AllegroSPB16.x is already on the market.
One more thing I want to mention is that Cadence not only provides the CadenceAllegro system interconnection design platform, but also provides IC design tools. I think in the near future, IC design will also be a must for electronic engineers. Lessons, just as it is common to make PCB boards now, I think it will be common to make ICs in the future. For example, there are companies such as SMIC in mainland China that can undertake such projects, but for ordinary users, it may be It will only take a period of time. Coupled with the improvement of the situation in Taiwan, the chip manufacturing industry is even more promising. Therefore, it is necessary to master one or two chip design software, I think.
PADS/PowerPCB
Although PADSPower appeared late and has not been understood by the majority of users, it not only continues PADS’s powerful functions "Easy to operate" features and greatly improved, so it is likely to be accepted by the majority of electronic circuit designers. It may be because it is closely related to PCB board manufacturing. Starting from PowerPCB5.0, it slowly gains popularity. Therefore, many people know PowerPCB. For some of the names of PADS and PowerPCB, I think it can be understood that the names of different versions are somewhat inconsistent. The original PADS series includes PowerLogic (schematic diagram tool), PowerPCB (PCB tool), HyperLynx (signal analysis tool) and other major tools. The most recent version of PADS2007 that is currently used includes DxDesigner (project management), PADSLogic (schematic diagram tool), PADSLayout (PCB tool), HyperLynx (signal analysis tool) and other major tools. So far, whether it is from schematic design, PCB design, high-speed signal analysis, or overall project management, etc., PADS has indeed become a comprehensive and powerful EDA software.