Basic Introduction to PCB Design Circuit Diagram

I knocked on the blackboard: Before PCB design, let's talk about some basic knowledge.

 

Circuit Diagram Definition: an electrical diagram that uses various electrical symbols, annotated boxes, and simplified shapes to represent the interrelationship of systems, equipment, devices, and components.

 

circuit diagram: When people install, debug, repair and study electrical equipment, they can analyze the circuit (, it is no wonder that I saw our maintenance engineer take a schematic diagram to repair the board there. I used to work as an SMT engineer with silk screen drawings.), without having to look at the circuit board over and over again, looking at the circuit diagram not only saves time and effort. Similarly, the work of designing circuits can also be carried out on paper or on a computer, which improves work efficiency.

 

circuit diagrams

 

1, according to the working voltage circuit can be dividedStrong electric circuitandweak current circuittwo kinds.

 

(1) Strong electric circuit

Strong electric circuit generally refers to the circuit whose working voltage exceeds 36V AC voltage, such as electric lights, desk lamps, range hoods, rice cookers, electric water heaters, heaters, refrigerators, air conditioners, washing machines and other electrical appliances in the family. Electric equipment.

 

(2) weak current circuit

 

weak current circuits are usually called electronic circuits. They generally refer to circuits with a power supply voltage of less than 36V, such as the main board circuits of electrical equipment such as televisions, color monitors, stereos, induction cookers, and computer-controlled refrigerators, air conditioners, and washing machines. The computer board circuits of small household appliances are all weak current circuits.

 

At present, many electronic products include not only strong current circuits, but also weak current circuits. For example, the switching power supply, output circuit and kinescope degaussing circuit of color TV belong to the strong current circuit, while the small signal processing circuit belongs to the weak current circuit.

 

2, circuit diagram according to the function can be dividedschematics, block diagrams, wiring diagrams and printed board diagrams, etc. (I used to be superficial, I thought the circuit diagram was the schematic diagram).

 

(1) Schematic Diagram

 

schematic diagram is used to reflect the working principle of the circuit of a circuit diagram, also known as "circuit schematic or electrical schematic diagram". This circuit diagram directly reflects the structure and working principle of the circuit, and is mainly used to design and analyze the circuit.

When analyzing the circuit, the actual working condition of the circuit can be understood by identifying the symbols of various circuit components drawn on the drawings and the connection between them. At the same time, in addition to showing the working principle of the circuit in detail, the schematic diagram can also be used as the basis for selecting components and making circuits (I personally think it is mainly used for PCB design).

 

(2)

 

block diagram is a circuit diagram that uses boxes and lines to represent the working principle and composition of the circuit. This is a special kind of schematic. 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 functions, and depicts each part as a box. Simple text is added to the box, and the relationship between the boxes is explained by connecting lines (sometimes connecting lines with arrows). Therefore,block diagram can only roughly illustrate the working principle of the circuit.

 

(3) Wiring Diagram

 

wiring diagram shows the whole piece of strong electrical products and the wiring inside the components. It is drawn according to the requirements of the circuit schematic diagram and the relative position of each component and wiring position in the equipment. It mainly expresses the relative position relationship between each component and assembly and the actual position of the wiring point,components or parts unrelated to wiring can be omitted.

 

(4) printed board drawing

 

printed circuit board diagram is the printed circuit board diagram, which is used for assembling actual circuits (that is, the PCB I see every day in the factory).

 

-made circuit board is to first apply a layer of metal foil on an insulating board, and then corrode the metal foil that is not needed for the circuit. The remaining part of the metal foil is used as the connecting line between the circuit components, and then the components in the circuit are installed on this insulating board. The remaining metal foil on the board is used as the conductive connecting line between the components to complete the circuit connection.

, because one or both sides of this circuit board are covered with copper, the printed circuit board is also called"copper-coated plate".

 

printed circuit board, it is not only necessary to consider whether the distribution and connection of all components are reasonable, but also to consider the volume and heat dissipation of the components, so the printed circuit board diagram and the schematic diagram are quite different.

 

With the development of science and technology, the production technology of printed circuit boards has been greatly improved. In addition to single-panel and double-panel, there are also multiple panels, which have been widely used in daily life, industrial production, national defense construction, aerospace and other fields.

 

circuit diagram

 

, because electrical products are composed of many electronic components, the circuit diagram will reflect the composition of the circuit through the corresponding circuit symbols, and these circuit symbols need to be connected and annotated. Therefore, the circuit diagram is mainly composed of component symbols, drawing symbols and comments (text symbols).

 

1. Component Symbols

 

component symbol represents the components in the actual circuit, and its shape is not necessarily similar to the actual components, or even completely different. But it generally shows the characteristics of the components, and the number of pins and the actual application of the components are exactly the same or basically the same, such as resistors, heaters, switches, fuses, diodes circuit symbols, as shown in Figure 1-2.

Figure 1-2 Circuit Symbols of Common Components

 

2. Drawing symbols

 

circuit diagram, there must be various symbols that represent voltage, current, and waveforms, and these symbols need to be connected, ground wire, wire and connection point, etc., to form a complete circuit diagram. Common drawing symbols are shown in Table 1-1 ~ Table 1-3.

Table 1-1 Voltage and Current Symbols

Table 1-2 Symbols of Conductor and Connection Point

Continuation

 

Table 1-3 Grounding and other symbols

Continuation

 

 

3. Notes

 

circuit diagram belong to the comment section, which is also an important part of the circuit diagram.

is mainly used to explain the name, model, main parameters, etc. of the components, and is usually marked next to the circuit symbols of the components. as shown in fig. 1-2, the letters "r" and "FU" respectively indicate that the symbols of the components are resistors and fuses.

In addition, many more complex circuit diagrams also annotate important power circuits, special devices and other parts. Therefore, the comment part is one of the important basis for circuit recognition.

 

circuit diagrams

 

want to learn to understand the circuit diagram, we must understand the drawing rules of the circuit diagram.

 

1. Arrangement of components

First of all, various components should be arranged from left to right and from top to bottom on the circuit diagram. The input part of the circuit should be arranged on the left side and the output part should be arranged on the right side. Secondly, the arrangement direction of components should be parallel or perpendicular to the edge of the drawing, and try to avoid diagonal arrangement. Finally, the layout of the circuit symbols of the components should be balanced, sparse and dense, so that the drawings are neat, concise and beautiful.

 

2. Drawing of wire

circuit diagram are required to be horizontal, flat and vertical, and the bends should be right angles. The following describes the drawing of the wire in several cases.

 

(1) wire

on the circuit diagram, there are several ways to connect the wires, one is a "T"-shaped connection, and the other is a ""-shaped connection. For the "T"-shaped connection wires, their connection points can be added with solid black dots or not, as shown in Figure 1-3(a). For crossing wires, if the two lines are connected, black dots should be added; if the two lines are not connected, black dots cannot be added, as shown in Figure 1-3 (B).

Fig. 1-3 Wire Connection Status

 

(2) Summary drawing of connected lines

When there are too many lines, many circuit diagrams draw multiple lines into a summary line (the summary line is not thickened) in order to reduce the number of lines. The junction is represented by a 45 angle or rounded corner, and the two ends of each summary line are marked with the same number or character, as shown in Figure 1-4.

Figure 1-4 Summary of Connections

Tips

4 oblique lines on the single line shown in Figure 1-4(a) indicate that the number of summarized lines is 4. Continuous summary drawing is a kind of continuous drawing, the so-called continuous drawing refers to the connection of the head and tail is connected.

 

(3) Interrupt drawing of connection

interrupt drawing means that the head and tail of the line are interrupted, and the interruption is marked with the same number or character, as shown in Figure 1-5.

Figure 1-5 Interruption Drawing of Connections

 

3. Drawing of Actionable Components

 

actionable (operable) components in the figure. If there is no special explanation, the rules are as follows.

 

(1) Switch

the common switch is in the open position and the transfer switch is in the open position or representative position as shown in FIGS. 1-6.

Figure 1-6 Switch Drawing

 

(2) relay

relay is in a static state before energization, the contact of the normally open relay is in an off state, and the contact of the normally closed relay is in an on state, as shown in Figure 1-7.

Figure 1-7 Relay Contact Status

Tips

some circuit diagrams are drawn separately from the coil and contact of the relay for clarity and conciseness, but they must use the same position code. In addition, the contacts of the AC contactor and the reed switch are usually in the open position.

 

4. Drawing of components

 

work together to complete a task in a circuit, regardless of their position in the actual circuit, they can be drawn together when drawing. Sometimes, the group of components will also draw a dotted outline.

 

the above content by the focus of the PCB design of Alice Jin Hengda editor, such as reproduction, please contact us.