Diodes come in various sizes, power ratings, voltages, currents, and frequencies. They are also classified differently based on their functions, which makes it essential to refer to the manual for proper usage. For a quick comparison, you can look at the package size—the larger the diode, the higher the current capacity (though not always directly related to voltage), and the bigger the heat sink typically is.
1. **Detector Diode**
Detector diodes are used to extract low-frequency signals from high-frequency ones. Their point-contact structure gives them a small junction capacitance and high operating frequency. They are usually made of tantalum or germanium and operate at frequencies up to 400 MHz. These diodes are often used in clipping, modulation, mixing, and switching circuits, as well as detection. Special two-diode assemblies are also used for FM detection.
2. **Rectifier Diode**
These diodes convert AC to DC. The boundary is generally set at 100 mA, with output currents above that. They have a large junction capacitance and are suitable for low-frequency applications, typically below 3 kHz. Common types include silicon rectifier diodes (2CZ), bridge rectifiers (QL), and high-voltage TV rectifiers (2CLG).
3. **Limiting Diode**
When forward-biased, these diodes maintain a nearly constant voltage drop (around 0.7V for silicon, 0.3V for germanium). This property allows them to limit signal amplitude. While most diodes can act as limiters, specialized ones like Zener diodes or protection meters are used for more precise control. Silicon-based diodes are often preferred for strong limiting effects.
4. **Modulation Diode**
Usually refers to ring modulators, consisting of four diodes with positive forward characteristics. Though other varactors may be used for frequency modulation, dedicated modulation diodes are designed for this purpose.
5. **Mixer Diode**
Used in mixers, these diodes operate in the 500–10,000 Hz range. Schottky and point-contact types are commonly used due to their fast response.
6. **Amplifying Diode**
Includes tunnel diodes, body-effect diodes, and varactor diodes. These use negative resistance or parametric amplification for signal boosting, often in high-frequency applications.
7. **Switching Diode**
These diodes switch between conducting and non-conducting states based on applied voltage. They are used in logic circuits, with fast switching speeds being a key feature. Schottky diodes are ideal for high-speed switching due to their short recovery time.
8. **Varactor Diode**
Also known as a tuning diode, it changes its capacitance with reverse voltage, making it useful for automatic frequency control (AFC) and tuning. It’s widely used in TV tuners and oscillating circuits.
9. **Frequency Multiplication Diode**
Varactor and step-recovery diodes are used to multiply frequencies. Step-recovery diodes produce sharp transitions, generating harmonics useful in microwave circuits.
10. **Zener Diode**
These diodes regulate voltage by utilizing reverse breakdown. Available in various voltage ranges (3V–150V), they are used in power supplies and voltage references. They come in different power ratings and have temperature-dependent characteristics.
11. **PIN Diode**
This diode has an intrinsic layer between P and N regions. At high frequencies, it behaves as a variable impedance element, used in microwave switching and phase shifting.
12. **Avalanche Diode**
Generates high-frequency oscillations through avalanche breakdown, used in microwave oscillators.
13. **Tunnel Diode**
Utilizes quantum tunneling to create negative resistance, used in high-frequency amplifiers and oscillators.
14. **Step Recovery Diode**
Designed to quickly turn off after conduction, producing rich harmonic content for use in pulse and frequency generation circuits.
15. **Schottky Diode**
Has a lower forward voltage drop and fast switching speed, ideal for high-frequency and RF applications. Also used as a freewheeling diode in power supplies.
16. **Damping Diode**
Used in high-voltage, high-frequency circuits for damping and boosting, such as in TV line scanning.
17. **Transient Voltage Suppressor (TVS) Diode**
Protects circuits from overvoltage spikes, available in bipolar and unipolar configurations with varying power levels.
18. **Double Base Diode (Unijunction Transistor)**
A three-terminal device used in relaxation oscillators and timing circuits, offering good stability and adjustability.
19. **Light-Emitting Diode (LED)**
Emits light when forward-biased, made from gallium phosphide or arsenide. Used in displays, lighting, and indicators, with recent developments including white LEDs.
20. **Silicon Power Switching Diode**
Offers high-speed switching and robust performance, used in power supplies, motor drives, and high-frequency rectification.
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