“Circuit is a professional basic course. Compared with cultural basic courses, it focuses more on solving practical engineering problems. Compared with professional courses, it emphasizes physical concepts and general theoretical analysis.
Circuit is a professional basic course. Compared with cultural basic courses, it focuses more on solving practical engineering problems. Compared with professional courses, it emphasizes physical concepts and general theoretical analysis.
Inventory of the five most practical circuit analysis methods
Block diagram recognition method
Figure 1-2 shows a block diagram of a two-stage audio signal amplification system. It can be seen from the figure that this system circuit is mainly composed of a signal source circuit, a first-stage amplifier, a second-stage amplifier and a load circuit. You can also know from this block diagram that this is a two-stage amplifier circuit.
Figure 1-2 Block diagram schematic diagram
Unit circuit diagram recognition method
Unit circuit refers to a certain level of controller circuit, or a certain level of amplifier circuit, or a certain oscillator circuit, frequency converter circuit, etc. It is the smallest circuit unit that can complete a certain circuit function. Broadly speaking, the application circuit of an integrated circuit is also a unit circuit.
In the process of learning the working principle of the Electronic circuit of the whole machine, the unit circuit diagram is the circuit diagram with complete functions first encountered. The concept of this circuit diagram is put forward for the convenience of the analysis of the working principle of the circuit.
1. Unit circuit diagram function
The unit circuit diagram has the following functions.
(1) The unit circuit diagram is mainly used to describe the working principle of the circuit.
(2) The unit circuit diagram 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. As shown in Figure 1-18, the variable resistor and the resistance value of the resistor are marked in the figure.
Figure 1-8 Schematic diagram
(3) The circuit diagram of the unit is very helpful to deeply understand the working principle of the circuit and the structure and composition of the memory circuit.
2. Features of unit circuit diagram
The unit circuit diagram is mainly for the convenience of analyzing the working principle of a certain unit circuit, and the circuit diagram of this part of the circuit is drawn separately, so other components and related connections and symbols that have nothing to do with the unit circuit have been omitted in the figure. , In this way, the unit circuit diagram is relatively simple and clear, and there is no interference from other circuits when recognizing the diagram, which is an important feature of the unit circuit. The power supply, input end and output end have been simplified in the unit circuit diagram. Figure 1-9 shows a unit circuit.
Figure 1-9 Schematic diagram of unit circuit diagram
(1) Power supply representation method. In the circuit diagram, +V is used to indicate the DC working voltage, where the positive sign indicates that the positive polarity DC voltage is used to supply power to the circuit, and the ground terminal is connected to the negative pole of the power supply; For power supply, the ground terminal is connected to the positive pole of the power supply.
(2) Input and output signal representation method. Ui represents the input signal, which is the signal to be amplified or processed by this unit circuit; Uo represents the output signal, which is the signal amplified or processed by this unit circuit.
Branch node method
A node is the meeting point of several branches in a circuit. The so-called branch node method is to number each node (agreement; the positive pole of the power supply is the first node, from the positive pole to the negative pole of the power supply, the nodes passed in order are 1, 2, 3…), and the branch starting from the first node Road, draw to the negative pole of the power supply. There may be multiple branches (regulation: different branches cannot pass through the same resistor repeatedly) to reach the negative pole of the power supply. The drawing principle is to draw the branch with fewer nodes first, and then the branch with more nodes. Then follow this principle to draw the branch starting from the second node. By analogy for the rest of the time, finally the remaining resistors are drawn according to the positions of their two ends.
Example 5: Draw the equivalent circuit shown in Figure 10.
Solution: In Figure 10, there are five nodes 1, 2, 3, 4, and 5. According to the principle of branch node method, from the positive pole of the power supply (the first node), there are two branches with a small number of nodes: R1, R2, R6 branch and R1, R5, R4 branch. Take one of the branches R1, R2, R6 and draw it as shown in Figure 11.
Starting from the second node, there are two branches that can reach the negative pole, one is R5, R4, and the number of nodes is 3, the other is R5, R3, R5, and the number of nodes is 4, and it is not advisable to have R6 repeated. Therefore, the R5 and R4 branches should be drawn again, and finally the remaining resistance R3 should be drawn, as shown in Figure 12.
Geometric deformation method
The geometric deformation method is to geometrically deform a given circuit based on the characteristics of the wire in the circuit that can be stretched, shortened, rotated or translated arbitrarily, further determine the connection relationship of the circuit components, and draw the equivalent circuit diagram.
Example 6: Draw the equivalent circuit of Figure 13.
Solution: shorten the wire of the ac branch and geometrically deform the circuit to get Figure 14. Then shrink ac to a point and bd to a point. It is obvious that R1, R2, and R5 are connected in parallel, and then connected in series with R4 (Figure 15).
Remove resistance method
According to the characteristics of series and parallel circuits, in a series circuit, if any resistor is removed and no current flows through the other resistors, these resistors are connected in series; in a parallel circuit, if any resistor is removed, the other resistors still have current through them, then these resistors are connected in series. It is connected in parallel.
Still taking Figure 13 as an example, suppose the current flows in from end A and flows out from end B. First remove R2. From Figure 16, we can see that R1 and R3 have current flowing. Then remove the resistor R1, and it can be seen from Figure 17 that R2 and R3 still have current flowing through it. Similarly, when the resistance R3 is removed, R1 and R2 also have current through the characteristics of the parallel circuit. R1, R2 and R3 are connected in parallel, and then connected in series with R4.
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