The difference between one-way and two-way TVS tubes

Transient Voltage Suppressor (TVS), abbreviated as TVS, is a high-performance protective device in the form of a diode. When the two poles of a TVS diode are subjected to a reverse transient high-energy impact, it can transform the high impedance between the two poles into low impedance at a speed of 10 ^ -12 seconds, absorbing surge power of up to several kilowatts, and clamping the voltage between the two poles at a predetermined value, effectively protecting precision components in the electronic circuit from damage caused by various surge pulses. It has the advantages of fast response time, high transient power, low leakage current, breakdown voltage deviation, easy control of clamping voltage, no damage limit, and small size. TVS diodes can be divided into unidirectional and bidirectional types, and the characteristics of unidirectional TVS diodes are similar to those of voltage regulators.

Working principle of TVS diode:

The device is connected in parallel in the circuit. When the circuit is working normally, it is in a cut-off state (high resistance state), which does not affect the normal operation of the circuit. When the circuit experiences abnormal overvoltage and reaches its breakdown voltage, it quickly changes from a high resistance state to a low resistance state, providing a low impedance conduction path for instantaneous current and clamping the abnormal high voltage within a safe level, thereby protecting the protected IC or circuit; When the abnormal overvoltage disappears, it returns to the high impedance state and the circuit works normally.

The forward surge current allowed by TVS can reach 50-200A under the conditions of TA=250C and T=10ms. Bidirectional TVS can absorb instantaneous high pulse power in both directions and clamp the voltage to a predetermined level. Bidirectional TVS is suitable for AC circuits, while unidirectional TVS is generally used for DC circuits. It can be used for lightning protection, overvoltage protection, anti-interference, and surge power absorption, making it an ideal protective device. Tolerance is expressed in watts (W).

TVS diodes can be easily integrated with other devices on a single chip. There are many devices that integrate EMI filtering and RFI protection functions with TVS diodes, which not only reduces the number of devices used in the design and lowers costs, but also avoids the associated self inductance that is easily induced during PCB wiring.

This ensures that the subsequent circuit components are not damaged by transient high-energy impacts. The response speed of TVS is definitely much faster than that of RC circuit. Unidirectional TVS is used to suppress reverse flow, and bidirectional TVS is used for AC flow.

TVS single/two-way difference:

1. Unidirectional use in DC. Two way use for communication;

2. The characteristics of a unidirectional TVS diode are similar to those of a voltage regulator diode, while the characteristics of a bidirectional TVS diode are equivalent to two voltage regulator diodes connected in reverse series;

3. The unidirectional capacitance Cj is larger than the bidirectional capacitance. Taking LRC as an example, the unidirectional capacitor C has 65PF, while the bidirectional capacitor has only 15PF;

4. All USB data cables are bidirectional;

5. The current curves are different. The circuit symbol of a unidirectional TVS transistor is the same as that of a regular voltage regulator, and its forward characteristic is the same as that of a regular diode, while its reverse characteristic is a typical PN junction avalanche device. Both forward and reverse directions of bidirectional diodes are typical PN junction avalanche devices.