​How to distinguish between single and bidirectional TVS transient suppression diodes

How to distinguish between single and bidirectional TVS transient suppression diodes

1、 How to distinguish between single and bidirectional TVS transient suppression diodes

1. Look at the model. From the surface of the model alone, we can judge that although different brands have different naming methods, there are rules:

2. Look at the specifications, usually on the page< 1> Bi-directional refers to bidirectional conduction, and<2>unidirectional refers to unidirectional conduction,

3. Measure with a multimeter

<1> Measure the gear position of the diode, with voltage on both sides of the unidirectional and bidirectional circuits;

<2> Direct current measurement, bidirectional symmetry, unidirectional only with reverse avalanche breakdown characteristics, usually measured at 1mA.

4. All TVS diodes will have a cathode line after amplification, which is used to distinguish the positive and negative poles of the diode and is independent of single or bidirectional.

2、 Differences in single/bidirectional usage

1. Unidirectional use for direct current. Used for two-way communication; The unidirectional TVS diode protection device can only protect positive or negative pulses, while the bidirectional TVS diode protection device is connected to one end to be protected

The circuit is grounded at one end, and ESD pulses from both reverse and forward directions are released, effectively protecting the IC.

2. TVS diodes can be divided into unidirectional and bidirectional. The forward characteristics of unidirectional TVS diodes are the same as those of ordinary voltage stabilizing diodes, and the hard breakdown at the reverse breakdown inflection point, which is approximately "right angle", is typical

PN junction avalanche. When there is an instantaneous overvoltage pulse, the current of the device suddenly increases while the reverse voltage rises to the clamping voltage value and remains at this level; V-I characteristics of bidirectional TVS diodes

The curve is like a "back-to-back" combination of two unidirectional TVS, with the same avalanche breakdown characteristics and clamping characteristics in both positive and negative directions. The Symmetric relation of the breakdown voltage on both sides is

0.9 ≤ VBR (positive)/VBR (negative) ≤ 1.1. Once the interference voltage applied at both ends exceeds the clamping voltage Vc, it will be immediately suppressed.

3. Interpolar capacitance Cj

Unidirectional capacitance C is larger than bidirectional capacitance C. Taking LRC as an example, unidirectional capacitance C has 65PF, while bidirectional capacitance C only has 15PF;

4. All USB data lines are bidirectional;

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