What does the differential diagnosis of transistors include?

Transistors are a commonly used electronic semiconductor device, widely used in amplification circuits, resonant circuits, digital circuits, and switching circuits. In specific use, transistors may malfunction and require identification and diagnosis. This article will introduce the identification and diagnostic methods of transistors.

1、 Static test

Static detection is one of the most commonly used identification and diagnostic methods, which can detect whether the PN junction of the transistor is normal and whether the amplification coefficient of the transistor is within the normal range.

1. PN junction detection

PN junction detection can be performed using a multimeter or diode detector. The test method is as follows:

(1) Receive the test poles of the multimeter or diode detector to the base and collector of the transistor respectively, and ground the other detection pole.

(2) Gently press the emitter of the transistor with your hand and observe the reading of the multimeter or diode detector.

(3) If the reading value is positive, it indicates that the PN junction is normal; If the reading value is negative, it indicates that the PN junction is broken.

2. Amplification coefficient detection

A multimeter or digital multimeter can perform amplification factor detection. The testing method is as follows:

(1) Receive the test poles of a multimeter or digital multimeter to the base and emitter of the transistor respectively, and ground the other test pole.

(2) Gently press the emitter of the transistor with your hand and observe the reading of a multimeter or digital multimeter.

(3) Remove the detection electrode from the emitter and observe if the reading has changed. If there is a change, it indicates that the transistor amplification coefficient is normal; If there is no change, it indicates that the transistor amplification coefficient is abnormal.

2、 Dynamic testing

Dynamic testing is a more accurate identification and diagnosis method that can detect the response time, frequency response, and degree of frame loss of transistors.

1. Detection response time

An oscilloscope can be used for response time detection. The testing method is as follows:

(1) Receive the probes of the oscilloscope to the base and emitter of the transistor respectively.

(2) Generate a square wave signal using a signal source and input it into the base of the transistor.

(3) Observe the response of the square wave signal on the oscilloscope. If the response speed of the transistor is very fast, the upper and lower edges of the square wave signal will be steeper; If the response speed of the transistor is slow, the upper and lower edges of the square wave signal will be relatively light.

2. Frequency response detection

Signal sources and oscilloscopes can be used for frequency response detection. The testing method is as follows:

(1) Receive the output end of the signal source to the base of the transistor, and the probe of the oscilloscope to the base and emitter of the transistor.

(2) Generate a sine wave signal using a signal source, change the number of signal sources, and observe the changes in the sine wave signal on the oscilloscope.

(3) If the frequency response of the transistor is normal, the amplitude and phase of the sine wave signal on the oscilloscope will vary with frequency; If the frequency response of the transistor is abnormal, the amplitude and phase of the sine wave signal on the oscilloscope will not change with frequency.

3. Frame loss level detection

The frame loss analyzer can perform frame loss level detection. The testing method is as follows:

(1) Receive the input of the lost frame analyzer to the base of the transistor and the output to the load.

(2) Use a signal source to generate a sine wave signal, change the range and frequency of the signal source, and observe the changes in the level of frame loss on the frame loss analyzer.

(3) If the degree of transistor dropout is small, the dropout level curve on the dropout analyzer will be relatively smooth; If the distortion level of the transistor is large, the curve of the dropout level on the dropout analyzer will be significantly distorted and deformed.

Generally speaking, the identification and diagnosis methods for transistors include static testing and dynamic testing. Static testing can detect whether the PN junction is normal and whether the amplification coefficient is within the normal range; Dynamic testing can detect the response time, frequency response, and frame loss degree of transistors. In practical applications, suitable testing methods can be selected based on the actual situation.

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