Basic knowledge and detection methods of crystal diodes 2

Maximum operating frequency FM: The frequency of the highest AC signal with unidirectional conductivity of a diode.

2. Commonly used diodes

(1) Rectifier diode

The diode that rectifies AC power into DC current is called a rectifying diode. It is a surface coupled power device with a large junction capacitance, resulting in a low operating frequency.

Usually, diodes with an IF of over 1 ampere are packaged in a metal shell to facilitate heat dissipation; All plastic packaging is used for IF below 1 ampere (see Figure 2). Due to the continuous improvement of modern technology, many high-power tubes have emerged abroad, which also use plastic packaging.

(a) Fully sealed metal structure

(b) Plastic packaging

(2) Detector diode

A detection diode is a device used to detect low-frequency signals superimposed on a high-frequency carrier, which has high detection efficiency and good frequency characteristics.

(3) Switching diode

In pulse digital circuits, the diode used to turn on and off the circuit is called a switching diode, which is characterized by a short reverse recovery time and can meet the needs of high-frequency and ultra-high frequency applications.

There are several types of switch diodes, including contact type, planar type, and diffusion table type. Generally, silicon switch diodes with IF<500mA are mostly sealed with epoxy resin and ceramic chip packaging, as shown in Figure 3. The longer end of the pin is the positive electrode.