Purpose of Diodes

Crystal diodes are often represented by "D" plus numbers in circuits,

Example:  D5 means diode number 5.

1. Function:

The main characteristic of the diode is unidirectional conductivity, that is, under the action of forward voltage, the on-resistance is very small; and under the action of reverse voltage, the on-resistance is extremely large or infinite. Because the diode has the above characteristics, it is often used in rectification, isolation, voltage regulation, polarity protection, coding control, FM modulation and squelch circuits 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, and Zener diodes.

2. Recognition 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, and some diodes are also represented by special symbols for diodes. P pole (positive pole) or N pole (negative pole), also use the symbol mark "P", "N" to determine the diode polarity. The positive and negative poles of the light-emitting diode can be identified from the length of the pins. The long pin is positive and the short pin is negative.

3. Test Notes:

When using a digital multimeter to measure the diode, the red test lead is connected to the positive electrode of the diode, and the black test lead is connected to the negative electrode of the diode. The resistance measured at this time is the forward conduction of the diode. Resistance value, which is just the opposite of the connection method of the pointer multimeter.