Basic knowledge and detection methods of crystal diodes 3

Figure 3. Silicon switch diode fully sealed ring epoxy resin ceramic chip package

(4) Zener diode

Zener diode is a surface bonded crystal diode made of silicon material. It utilizes the characteristic that the voltage during reverse breakdown of PN junction does not change with the current to achieve the purpose of voltage stabilization. Because it can play a stabilizing role in the circuit, it is called Zener diode (abbreviated as Zener diode), and its graphic symbol is shown in Figure 4

Figure 4: Symbols for Zener diodes

The volt ampere characteristic curve of the voltage regulator is shown in Figure 5. When the reverse voltage reaches Vz, even a small increase in voltage will cause a sharp increase in reverse current (the reverse breakdown curve is very straight). At this point, the diode is in a breakdown state. If the breakdown current is limited within a certain range, the transistor can operate stably in the reverse breakdown state for a long time.

Figure 5. Voltage current characteristic curve of silicon voltage regulator

(5) Varactor diode

Varactor diode is a nonlinear capacitive element made by utilizing the characteristic that the capacitance of PN junction changes with the applied bias voltage. It is widely used in microwave circuits such as parametric amplifiers, electronic tuning, and frequency multipliers. Varactor diode mainly highlights the nonlinear relationship between capacitance and voltage through a series of paths such as structural design and process, and improves the Q value to be suitable for application.