Difference between bidirectional and unidirectional TVS Diode — SUNMATE

TVs diodes are divided into bidirectional and unidirectional. What is the difference between these two types?

One end of the unidirectional TVS diode has a thin color ring, which is connected with the positive pole; Two rings are marked in the middle of the two-way TVs secondary tube, or there is no sign and no polarity. The bidirectional TVs tube can absorb the instantaneous high pulse power in the positive and negative directions and clamp the voltage to a predetermined level. Bidirectional TVs tubes are suitable for AC circuits, while unidirectional TVs tubes are generally used for DC circuits.

In reverse operation, the maximum pulse peak current allowed for the device to pass under the specified pulse conditions. The product of iPP and maximum clamping voltage VC (max) is the maximum value of transient pulse power. Unidirectional TVs transistors have the same forward characteristics as ordinary zener diodes.

The inflection point of reverse breakdown is approximately "right angle", which is a kind of hard breakdown and a typical PN junction avalanche device. From the curve from the breakdown point to VC value, it can be seen that when there is an instantaneous overvoltage pulse, the equipment current suddenly increases, and the reverse voltage rises to the clamping voltage value and remains at this level. TVs should be correctly selected in use so that the rated transient pulse power PPR is greater than the maximum transient surge power that may occur in the protected equipment or line. In the area where breakdown occurs, the voltage measured at both ends of the device under the specified test current I (BR) is called breakdown voltage. In this region, the diode becomes a low impedance path.