Definition:
A diode is a unidirectional conductive semiconductor device whose core structure is a PN junction (a combination of P-type and N-type semiconductors).
Key characteristics:
l Unidirectional conduction: conducts in forward bias (anode voltage > cathode voltage) and cuts off in reverse.
l Voltage drop: about 0.60.7V for a silicon diode and about 0.20.3V for a Schottky diode.
l Maximum parameters: Reverse withstand voltage (V_R), forward current (I_F).
Common types & applications:
Types | Characteristics | Typical Applications |
Rectifier diode | High voltage/high current (e.g. 1N4007) | AC/DC power rectification |
Schottky diode | Low drop, high speed | High-frequency switching circuit, reverse connection protection |
Voltage stabilizing diode | Reverse breakdown voltage stabilization | Voltage reference, overvoltage protection |
Light-emitting diode | Electroluminescence (LED) | Indicator lights, display screens |
Definition:
A Bipolar Junction Transistor (BJT) is a current-controlled semiconductor device with two polarities: NPN and PNP.
Key characteristics:
l Current amplification: Base current (I_B) controls collector current (I_C), amplification factor β (hFE).
l Working status:
¢ Cut-off area (switch off)
¢ Amplification zone (analog signal amplification)
¢ Saturation region (switch on)
Common types and applications:
Types | Structure | Conduction conditions | Typical Applications |
NPN | Collector - Base - Emitter | V_B > V_E + 0.7V | Switching circuits, signal amplification (e.g. 2N3904) |
PNP | Emitter - Base - Collector | V_E > V_B + 0.7V | Negative voltage switch (e.g. 2N3906) |
Typical circuit:
l Switching circuit: Base resistance controls the load on/off.
l Amplifier circuit: Common-emitter amplifier (audio /RF signal amplification).
3. TVS Diode (Transient Voltage Suppression Diode)
Definition:
TVS (Transient Voltage Suppressor) is a transient overvoltage protection device that responds extremely fast (in the ps range) to absorb surge voltages.
Key features:
l Working principle: Reverse breakdown discharge transient current (similar to a voltage stabilizing diode, but with greater power).
l Core parameters:
¢ Breakdown voltage (V_BR) : The voltage threshold that triggers protection.
¢ Clamp voltage (V_C) : A safe value at which transient voltage is limited.
¢ Peak pulse power (P_PPM) : such as 600W, 1.5kW.
Common types and applications:
Types | Characteristics | Typical Applications |
One-way TVS | Only suppress forward or reverse surges | DC power protection (such as USB port) |
Bidirectional TVS | Suppression in both forward and reverse directions | Ac circuits, signal line protection (e.g. RS485) |
Typical application scenarios:
l Interface protection: ESD protection for USB, HDMI, Ethernet ports (e.g. SMAJ5.0A).
l Power protection: Lightning strikes, inductive load surges (e.g. P6KE series for automotive 12V systems).
Devices | Core Functions | Key parameters | Typical application scenarios |
Diode | Unidirectional conduction | V_R, I_F, V_F | Rectification, reverse connection prevention, voltage stabilization |
Triode | Current amplification/switch | β (hFE), V_CE, I_C | Signal amplification, load switch |
TVS | Transient overvoltage protection | V_BR, V_C, P_PPM | ESD protection, power surge suppression |
1. Diode:
¢ Choose a rectifier circuit with a withstand voltage (V_R) greater than 2 times the input voltage.
¢ Use Schottky diodes for high frequency scenarios (low drop, fast recovery).
2. Triode:
¢ Switch circuits need to ensure that the β value is sufficient to drive the load current (e.g. I_C > I_load).
¢ For amplification circuits, pay attention to the design of the operating point in the linear region.
3. TVS diode:
¢ Clamping voltage (V_C) < withstand voltage of the protected device.
¢ Bidirectional TVS is used for AC or signal lines, while unidirectional TVS is used for DC power supplies.
l Power input protection:
Rectifier diodes + TVS form AC/DC front-end protection.
l Motor drive:
NPN transistor + freewheeling diode controls DC motor.
l ESD protection:
Bidirectional TVS protects the communication interface.
If specific model recommendations or circuit design guidance are needed, further requirements can be described!
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