TVS (Transient Voltage Suppression) A transient voltage suppression diode is a device used to protect electronic circuits from the interference of transient voltages (such as lightning strikes, electrostatic discharge, etc.). It can quickly absorb and consume excessive voltage when the voltage exceeds the normal operating range for a moment, so as to protect other sensitive components in the circuit from damage.

I. The working principle of TVS diode
    The basic principle of TVS diode is that when the voltage exceeds its specific trigger voltage, the TVS diode will be quickly switched on, and the high voltage generated by the short circuit will be suppressed in an instant to prevent the circuit components from being damaged by excessive voltage. When the voltage returns to the safe range, the on-state of the TVS diode will quickly return to the non-on-state.

Key points of working principle:
    Normal working state: In the circuit, the voltage at both ends of the TVS diode is usually lower than its breakdown voltage (commonly known as "clamp voltage"), and the TVS diode does not work at this time. At this time, the TVS diode is equivalent to an open circuit and does not affect normal signal transmission.
    Transient voltage event: When the circuit appears transient overvoltage (such as lightning strike, electrostatic discharge or switching noise, etc.), the voltage instantaneously exceeds the breakdown voltage of the TVS diode, the TVS diode quickly enters the on-state, and the excessive voltage is guided through its own low resistance path, reducing the voltage at both ends of the circuit to a safe value.
    Return to normal state: After the transient voltage disappears, the TVS diode returns to the non-on-state and no longer affects the circuit.

Ⅱ、Characteristics of TVS diode
    Clamping Voltage: The clamping voltage refers to the voltage at which the TVS diode starts conducting electricity, generally slightly higher than its operating voltage. When the transient voltage exceeds this voltage, the TVS diode will switch on, suppressing the overvoltage to an acceptable level.
    Breakdown Voltage: This is the voltage that the TVS diode is subjected to when there is no fault. Normally at this voltage, the diode will not conduct, but the voltage will slightly deviate from its normal operating voltage.
    Reverse Leakage Current: In the operating voltage range, the reverse current of the TVS diode should be very small, usually in the microampere level. This means that the TVS diode consumes almost no current and will not affect the normal circuit.
    Response time: The response time of TVS diodes is very short, usually in the nanosecond level, which can quickly suppress transient overvoltage and prevent it from causing harm to the circuit.
    Clamping Voltage: Clamping voltage is the voltage that the TVS diode can maintain while suppressing the transient voltage. The clamping voltage determines how well the circuit is protected against overvoltage.
    Energy Absorption Capability: TVS diode has a certain energy absorption capability, which can absorb the energy generated by transient voltage in a short time. Usually measured in joules (J), the greater the energy, the stronger the protection of the TVS diode.
    Transient current capacity: The transient current capacity of the TVS diode indicates the instantaneous current it can withstand. In general, the transient current capacity needs to be higher than the current generated by the transient voltage.

Ⅲ、Classification of TVS diodes
    Unidirectional TVS Diode: Unidirectional TVS diodes are usually used in direct current circuits or AC circuits with a single voltage polarity to protect the circuit from negative voltage. It can only effectively suppress forward overvoltage.
    Bidirectional TVS Diode: Bidirectional TVS diodes are suitable for AC circuits or direct current circuits with bipolar voltages. It can suppress both positive and negative transient voltages at the same time, providing bidirectional protection.
    SMD TVS Diode: This TVS diode is suitable for circuits with surface mount (SMT) technology. It is very useful in space-constrained applications.
    Traditional pin-type TVS Diode (Through Hole TVS Diode) : Circuits for through hole (THT) mounting technology, generally used in applications with high current and energy requirements.

Ⅳ、TVS diode application
    Communication equipment protection: Communication equipment is usually affected by transient voltages such as lightning strikes, electrostatic discharge, and switching noise. TVS diodes can be used to protect communication ports, modems, routers and other devices from damage.
    Automotive electronics: In automotive electronics systems, TVS diodes can be used to protect sensors, ECUs (electronic control units) and other components from high voltage damage. Automotive circuit systems often face the challenge of transient voltages such as electrical noise and lightning strikes.
    Consumer electronic equipment: TV, audio, computer and other consumer electronic equipment in the data interface (such as USB, HDMI) often face the threat of electrostatic discharge (ESD), TVS diodes can effectively protect.
    Power Systems and Industrial Control: Transient voltages in power systems and industrial control systems can cause equipment damage or data loss. TVS diodes can be used in high-voltage environments such as substations and automation equipment to ensure long-term reliability of equipment.
    LED lighting and power equipment: In LED lighting or power management systems, TVS diodes can protect the power circuit from overvoltage and transient current, extending the circuit life.

Ⅳ、TVS diode selection and precautions
    Select the right breakdown voltage: When choosing TVS diodes, it is necessary to determine the breakdown voltage according to the operating voltage of the circuit. The breakdown voltage should be slightly higher than the operating voltage of the circuit, but not too high, otherwise it can not effectively protect the circuit.
    Consider the amplitude and energy of the transient voltage: according to the amplitude and duration of the transient voltage that may appear in the circuit, select a TVS diode with sufficient energy absorption capacity and transient current capacity.
    Matching current and voltage characteristics: When selecting TVS diodes, ensure that their current carrying capacity and voltage characteristics match the operating conditions in the circuit.