Identification Techniques: Identification Methods and Functions of Crystal Diodes

Crystal diodes are commonly represented by "D" followed by a number in circuits, for example: D5 represents the diode numbered 5.

1. Function: The main characteristic of a diodes is unidirectional conductivity, which means that under the action of forward voltage, the conduction resistance is very small; Under the action of reverse voltage, the conduction resistance is extremely high or infinite. Because diodes have the above characteristics, they are often used in circuits such as rectification, isolation, voltage regulation, polarity protection, coding control, frequency modulation, and noise reduction in cordless telephones.

The crystal diodes used in telephones can be divided into rectifier diodes (such as 1N4004), isolation diodes (such as 1N4148), Schottky diodes (such as BAT85), light-emitting diodes, voltage regulators, etc. according to their functions.

2. Identification method: The identification of diodes is very simple. The N pole (negative pole) of low-power diodes is mostly marked with a color circle on the surface of the diode. Some diodes also use diode specific symbols to represent the P pole (positive pole) or N pole (negative pole), while others use symbol marks such as "P" and "N" to determine the polarity of the diode. The positive and negative terminals of a light-emitting diode can be identified by the length of its pins, with the long pin being positive and the short pin being negative.

3. Testing precautions: When using a digital multimeter to test a diodes, connect the red probe to the positive terminal of the diode and the black probe to the negative terminal of the diode. The resistance value measured at this time is the forward conduction resistance value of the diode, which is exactly the opposite of the probe connection method of a pointer multimeter.

4. The voltage withstand comparison of commonly used 1N4000 series diodes is as follows:

Model 1N4001 1N4002 1N4003 1N4004 1N4005 1N4006 1N4007

Voltage resistance (V) 50 100 200 400 600 800 1000

The current (A) is all 1