TVS is a new type of high efficient circuit protection device, which has a fast response time (sub nanosecond) and very high surge absorption capability. When the two ends of which are subjected to high energy impact moment, TVS at high speed, the impedance between the two values from high impedance to low impedance, to absorb a large transient current, thus the voltage clamp it at a predetermined value, the circuit element is not affected by the impact of transient pressure in order to protect the back of spike pulse. Because of this, the TVS tube can be used to protect the device or circuit from static, inductive load switching transient voltage [4], as well as the lightning induced over-voltage. Figure 1 shows the symbol and volt ampere characteristic curve of the TVS tube. TVS tube and voltage regulator, but also the reverse application. VR, which is called the maximum turning voltage, is the critical voltage before reverse breakdown. VB is the breakdown voltage, which corresponds to the reverse current IT is generally valued at 1 mA. VC is the maximum clamping voltage, when the peak current in the TVS tube is a high current of IPP, the voltage at the two ends of the tube will no longer rise. Therefore, the TVS tube can always protect the device or device port voltage limited to VB to VC effective area.
TVS tube and the regulator is different, the value of IPP can reach hundreds of amperes, and the clamp response time is only 1 * 10-12s. The maximum allowable pulse power of TVS tube is PM=VCIPP, and the greater the power consumption PM is, the greater the withstand capacity of inrush current is under the given maximum clamping voltage.
Figure 2 shows the current and voltage waveforms of the TVS tube observed in the double trace oscilloscope. Figure 1, the curve of 1mA is the current waveform in the TVS tube, we can see: the current flowing through the TVS tube suddenly rose to the peak value, and then decreased according to the exponential law. Curve 2 is the voltage waveform at both ends of the TVS tube, which indicates that the current in the TVS tube rises abruptly, and the voltage of the TVS tube rises. Under the action of surge voltage, the voltage between the two poles of the TVS tube is broken by the rated reverse turn off voltage VRWM to the breakdown voltage VB. With the emergence of the breakdown current, the current flowing through the TVS tube will reach the peak pulse current IPP, while the voltage at both ends of the clamp is clamped to a predetermined maximum clamping voltage of VC.
Then, with the pulse current according to the exponential decay, the process of TVS tube voltage between the two poles has been declining, finally restored to the original state, this is the TVS tube surge suppression pulse power may occur, the process of protection of electronic components. In fact, when the TVS pipe poles by the reverse high energy impact, it can with the 10-12s speed, the impedance between two changes from high to low, to absorb up to several kilowatts of power surge, the voltage clamp between the two poles in a predetermined value, so as to effectively protect the components in electronic equipment from ESD damage.