1. Selection of detection diode
Point-contact germanium diodes are generally used for detection diodes, such as 2AP series. When selecting, the detection diode with high operating frequency, small reverse current and large forward current should be selected according to the specific requirements of the circuit. Although the principle of detection and rectification is the same, the purpose of rectification is only to obtain direct current, while detection is to remove the signal component (envelope) from the modulated wave. The detection circuit and the half-wave rectifier circuit are exactly the same. Because the detection is a high-frequency wave rectification, the junction capacitance of the diode must be small, so the point contact diode is selected. Most of the diodes that can be used for high-frequency detection can be used in limiting, clamping, switching, and modulation circuits.
Replacement of detection diodes
After the detection diode is damaged, if there is no replacement of the same type of diode, the diode near the primary parameter with the same semiconductor data can also be used to replace it. In amateur conditions, a germanium high-frequency transistor with a damaged PN junction can also be used instead.
2. Selection of rectifier diode
The rectifier diode is generally a planar silicon diode, which is used in the rectifier circuit of the CPPCC power supply.
When selecting a rectifier diode, the first consideration should be its maximum rectifier current, large reverse operation current, cut-off frequency and reverse recovery time and other parameters.
Generally, the rectifier diode used in the series regulated power supply circuit does not have high requirements for the reverse recovery time of the cut-off frequency, and only needs to select the rectifier diode that meets the requirements of the large rectifier current and the large reverse operation current according to the requirements of the circuit.
The rectifier diode used in the rectifier circuit and pulse rectifier circuit of the switching regulated power supply should be selected with a rectifier diode with a high operating frequency and a short reverse recovery time or a fast recovery diode.
Replacement of rectifier diodes
After the rectifier diode is damaged, it can be replaced with the same type of rectifier diode or other types of rectifier diodes with parameters.
In general, a rectifier diode with a high withstand voltage (reverse voltage) can replace a rectifier diode with a low withstand voltage value, while a rectifier diode with a low withstand voltage value cannot replace a rectifier diode with a high withstand voltage value. A diode with a high rectifier current value can replace a diode with a low rectifier current value, while a diode with a low rectifier current value cannot replace a diode with a high rectifier current value.
3. Selection of voltage regulator diode
Zener diodes are generally used as voltage references in regulated power supplies or as maintenance diodes in overvoltage maintenance circuits.
The selected voltage regulator diode should meet the requirements of the primary parameters in the use circuit. The stable voltage value of the Zener diode should be the same as the reference voltage value of the circuit used, and the maximum stable current of the Zener diode should be about 50% higher than the maximum load current of the used circuit.
Replacement of regulator diodes
When the Zener diode is damaged, it should be replaced with a Zener diode of the same type or a Zener diode with the same electrical parameters.
A high dissipation power Zener diode with the same stable voltage value can be used to replace a Zener diode with a low dissipation power, but a Zener diode with a low dissipation power cannot be used to replace a Zener diode with a high dissipation power. For example, a 0.5W, 6.2V Zener diode can be replaced with a 1W or 6.2V Zener diode.
4. Selection of switching diodes
The role of a switching diode is to use its unidirectional conductivity to make it a more ambitious electronic switch. In addition to satisfying the requirements of general diodes and performance indicators, switching diodes also have outstanding high-frequency switching characteristics (short reverse recovery time), and are widely used in home appliances, computers, televisions, communication equipment, household audio, DVD players, instrumentation, control circuits, various high-frequency circuits and electronic equipment such as switching circuits, detection circuits, high-frequency pulse rectifier circuits, etc.
Switching diodes are divided into general switching diodes, high-speed switching diodes, ultra-high-speed switching diodes, low-power switching diodes, high-backvoltage switching diodes, silicon voltage switching diodes, etc. For medium-speed switching circuits and detector circuits, 2AK series general switching diodes can be selected. High-speed switching circuits are selected based on the primary parameters of the circuit (e.g., forward current, high reverse voltage, reverse recovery time, etc.).
Switching diode substitution
When a switching diode is damaged, replace it with a switching diode of the same type or replace it with another type of switching diode with the same primary parameters.
High-speed switching diodes can replace general switching diodes, and switching diodes with high reverse breakdown voltage can replace switching diodes with low reverse breakdown voltage.
5. Selection of varactor diode
When selecting varactor diodes, we should focus on whether the parameters such as its operating frequency, high reverse operating voltage, large forward current and zero bias junction capacitance meet the requirements of the circuit used.
Varactor diode substitution
If a varactor diode is damaged, it should be replaced with a varactor of the same type as the original type or with another type of varactor diode with the same primary parameters (especially if the junction capacitance range should be the same or nearby).
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