In the circuit board, no matter what type of circuit board is basically by: power supply circuit, input interface circuit, microprocessor control circuit, output interface circuit, display circuit, protection circuit and communication circuit, etc. 7 most of the circuit composition. As long as we master the seven types of circuit structure and control principle, know the structure of each type of circuit characteristics and key components, can judge in the circuit board each part of the circuit belongs to that type of circuit, familiar with the fault law and characteristics of each type of circuit, we can for various types of circuit board maintenance.

Power supply circuit: power supply circuit is a part of the circuit that provides energy to each unit circuit in the whole circuit board. It works in the environment of high voltage and high current, and is the most prone to failure.

The function of the power supply circuit is to convert 220VAC or 380VAC AC into various levels of DC with constant output voltage of ±5V, 12V, 15V, 18V and 24V required by the circuit board.

Input interface circuit: The input interface circuit is a part of the circuit for information exchange and communication between the circuit board and the outside world. It can convert what people want to say or do to the circuit board into electrical signals that can be recognized by the microprocessor in the circuit board. For example: When we are monitoring the temperature, if you say to the microprocessor in our common human communication language that the temperature is too high, please turn it down a little, the microprocessor will not understand what we say. At this time, we can convert the temperature signal into electrical signal by using thermistor or thermocouple components through the interface circuit, and then process the converted electrical signal. You get an electrical signal that the microprocessor recognizes. That way, when the microprocessor understands what we want it to do, it can do what we want it to do. The same is true for other signals such as illumination, pressure, wind, liquid level, position and so on.

The function of the input interface circuit is to convert what people want to say or do to the circuit board into a level signal that the microprocessor in the circuit board can recognize.

Microprocessor control circuit: microprocessor control circuit is mainly used in the main control board circuit board, when we see the circuit board looks like long square or rectangular shape, there are many pins, next to the crystal oscillator, this component is mostly microprocessor components, microprocessor as the core component around is the microcontroller circuit.

The main function of the microprocessor control circuit is to receive the relevant information sent by the input interface circuit, and analyze and process the information, and make the corresponding processing results, the processing results are further sent to the output interface circuit.