crystal diode

Crystal diodes are usually represented by "d" plus numbers in circuits, for example, D5 means diodes numbered 5.
1. Function: the main characteristic of diode is unidirectional conductivity, that is, under the action of positive voltage, the on resistance is very small; while under the action of reverse voltage, the on resistance is very large or infinite.
Because of the above characteristics, the diode is often used in rectifying, isolating, stabilizing voltage, polarity protection, coding control, frequency modulation, squelching and other circuits in cordless telephone.
The crystal diodes used in the telephone can be divided into:
Rectifier diode (such as 1N4004), isolation diode (such as 1N4148), Schottky diode (such as BAT85), led, zener diode, etc.
2. Recognition method: the recognition of diode is very simple. The N-pole (negative pole) of small power diode is usually marked with a kind of color circle on the surface of diode. Some diodes also use diode special symbol to represent P-pole (positive pole) or N-pole (negative pole), and also use symbol mark "P" or "n" to determine the polarity of diode.
The positive and negative poles of the LED can be identified by the length of the pin. The long pin is positive and the short pin is negative.
3. Test precautions:
When using the DMM to measure the diode, the red probe is connected with the positive pole of the diode, and the black probe is connected with the negative pole of the diode. At this time, the measured resistance is the positive on resistance of the diode.aa