Understand the single and double directions and differences of transient suppression diodes
Transient suppression diodes can protect sensitive electronic equipment from the impact of voltage transients caused by lightning surge and other transient voltage events, and are widely used in current circuit protection. Many customers do not know much about the product itself, such as what is one-way or two-way, and what are their differences. This has led to some customers' difficulties in choosing.
1、 How to distinguish single and two-way TVS transient suppression diodes
1. Look at the model. From the model surface alone, we can judge that although different brands have different naming methods, there are laws:
2. The specifications are usually on the page< 1> Two way is two-way conduction,<2>one way is one-way conduction,
3. Measure with multimeter
<1> Measure the gear position of the diode. There is voltage on both sides of both directions;
<2> DC measurement, bidirectional symmetry, unidirectional only reverse is avalanche breakdown characteristic, generally measured at 1mA.
4. After all TVS tubes are amplified, there will be a cathode line, which is used to distinguish the positive and negative poles of the diode, independent of single and two-way.
2、 Differences in single/two-way use
1. One way is used for DC. Two way communication; One way TVS tube protective device can only protect positive pulse or negative pulse, while one end of two-way TVS tube protective device is connected with
One end of the line is grounded, and ESD pulses from both reverse and forward directions are released, which effectively protects the IC.
2. TVS tubes can be divided into unidirectional TVS tubes and bidirectional TVS tubes. The forward characteristic of unidirectional TVS tubes is the same as that of ordinary voltage stabilizing diodes. The hard breakdown at the inflection point of reverse breakdown, which is approximately "right angle", is typical
PN Knot Avalanche. When there is an instantaneous over-voltage pulse, the current of the device increases rapidly and the reverse voltage rises to the clamping voltage and remains at this level; V-I characteristics of bidirectional TVS tubes
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 symmetrical relationship between the breakdown voltages on both sides is
0.9 ≤ VBR (positive)/VBR (negative) ≤ 1.1. Once the interference voltage applied to its two ends exceeds the clamping voltage Vc, it will be immediately suppressed.
3. Inter pole capacitance Cj
The unidirectional capacitor is larger than the bidirectional capacitor. Take the LRC as an example, the unidirectional capacitor C has 65PF, and the bidirectional capacitor C has only 15PF;
4. All two-way USB data lines;
5. The current curve is different. The circuit symbol of the unidirectional TVS tube is the same as that of the ordinary voltage stabilizing tube, its forward characteristic is the same as that of the ordinary diode, and its reverse characteristic is a typical PN junction avalanche device. The forward and reverse directions of bidirectional diodes are typical PN junction avalanche devices.
