Circuit Diagram Recognition 5-How to Recognize Complex Circuit Diagrams

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Circuit Diagram Recognition 5-How to Recognize Complex Circuit Diagrams [Copy link]

When looking at complex circuit diagrams, we should follow the ideas and methods from the local to the whole, from input to output, breaking the whole into parts, and gathering the parts into a whole. We should use the working principle of the whole circuit to guide the unit circuit, and use the unit circuit to analyze the working principle of the whole circuit.

TV circuit block diagram

1. Recognize the diagram by understanding the function

Before performing circuit diagram recognition, you must be clear about the functions and characteristics of the electronic product that needs to be recognized. For example, the remote control used for televisions and air conditioners, its main function is that when the key corresponding to the required operation function is pressed, the operation key input end of the microprocessor will receive the key control pulse, which will be recognized and processed by the microprocessor and output the control signal. The control signal is then amplified by the amplifier circuit and transmitted by the infrared transmitting tube. After the infrared signal is finally received by the receiving circuit on the controlled device, the control function required by the user can be realized. Therefore, in order for the remote control to work properly, it is necessary to set up a power supply circuit, a microcontroller (single-chip microcomputer), an operation key, an amplifier circuit, and an infrared transmitting diode. Understanding the product function can help understand the composition and working principle of the circuit.

Second, recognize the image by breaking the whole into parts

First, divide the whole circuit into several unit circuits according to different functions. How many unit circuits are divided depends not only on the structure and complexity of the circuit, but also on the amount of electronic technology knowledge and the ability to recognize images. The divided unit circuits should be classified and analyzed according to their characteristics. For example, a self-excited switching power supply is composed of a starting circuit, an oscillation circuit, an error sampling circuit, a pulse width circuit, an output voltage rectification/filtering circuit, and a protection circuit; for another example, a color TV line scanning circuit is composed of a line oscillator, a line excitation circuit, and a line output circuit.

Self-excited switching power supply

3. Recognize the drawing according to the characteristics of components

It is easier to find the required unit circuit through the circuit symbols or actual objects of electronic components. For example, when reading the diagram of a color TV circuit, the power supply circuit can be identified through the power transformer, the row excitation circuit can be identified through the row excitation transformer, the audio circuit can be identified through the speaker, the microprocessor circuit can be identified through the large-scale integrated circuit and the crystal oscillator, and the field output circuit can be identified through the field output integrated circuit. For another example, when reading the diagram of an induction cooker circuit, the power conversion circuit can be identified through the resonant coil (coil), the synchronous control circuit can be identified through the large current limiting resistor, the heat dissipation system can be identified through the fan, and the buzzer circuit can be identified through the buzzer.

Line excitation transformer

4. Recognize the diagram according to the power supply direction

Any electronic product needs to obtain the working voltage provided by the power circuit before it can work. Many complex electronic products use a variety of power supply methods, so by observing the direction of the power supply voltage, you can preliminarily identify the circuit diagram. For example, the microprocessor of an induction cooker uses 5V power supply, while its power tube excitation circuit and protection circuit mostly use 18V power supply; for another example, the microprocessor circuit of an ordinary color TV uses 5V power supply, the small signal processing circuit uses 12V power supply, the field output circuit mostly uses 20~110V power supply, and the line output circuit mostly uses 105~150V power supply. 5. Recognize the diagram according to the signal flow 34)]Any signal processing circuit will have signal input and signal output circuits, so the circuit can be decomposed into multiple unit circuits according to the signal flow, and it can be analyzed. For example, the field scanning circuit of a color TV can be divided into field synchronization circuit, field oscillation circuit, field excitation circuit, and field output circuit according to the signal flow.

[color=rgb(34, 34,6. Identify the diagram according to the AC equivalent circuit

First, draw the AC equivalent circuit, and then analyze the AC state of the circuit, that is, when the circuit has a signal input, whether the voltage and current of each link in the circuit change according to the law of the input signal, so as to confirm whether the circuit is an amplifier circuit, an oscillator circuit, or a limiter, clipper, shaper, phase detector, etc.

34)]When drawing an AC equivalent circuit, the capacitor and power supply in the original circuit should be drawn as a path, and the coil should be regarded as an open circuit, as shown in the figure below.

Seven, according to the DC equivalent circuit diagram

Draw a DC equivalent circuit diagram, analyze the DC system parameters of the circuit, clarify the static operating point and bias properties of the transistor, the inter-stage coupling method, etc., and analyze the state of the relevant components in the circuit and the role they play. For example: the working state of the transistor, such as saturation, amplification, and cut-off regions. The diode is on or off, etc.

When drawing a DC equivalent circuit, the coil in the original circuit should be drawn as a path and the capacitor as an open circuit. As shown in the figure below.