In the design, the use of the TVS tube, in the previous design, if you do not pay special attention to the TVS tube, then following a small series together with a detailed understanding of it.
TVS is a protective device. It‘s English called transient voltage suppressor, means the transient voltage suppressor. TVS tube is a diode type device. The principle is a bit like zener diode, are the use of reverse breakdown stable voltage, but the response speed of the TVS tube faster than the regulator. When the TVS tube by the reverse transient high energy shock is that it can at very high speed (subnanosecond) impedance between the two stages into a low impedance, so it has good ability to absorb surge power, but also can make the voltage between the two levels is maintained at a predetermined value, other effective components to protect the circuit from damage surge pulse.
By the way, the TVS tube and the regulator to compare the two:
Same point
1, can be limited to both ends of the voltage in a certain range.
2, long time flow resistance value almost, with volume power consumption.
Difference
1, the accuracy of voltage regulator voltage regulator is more accurate, TVS is in a range
2, the flow capacity regulator tube resistance surge current is very small, but TVS can reach hundreds of A
3, the principle of the regulator is Zener tunneling effect or avalanche effect, TVS is the avalanche effect
4, the application of voltage regulator for voltage stabilization, TVS for transient high voltage protection
5, voltage regulator voltage regulator 3.3V~75V, TVS tube 6.8V ~ 550V
6, response time TVS can reach 1ps
After comparison, it is clear that the zener diode and TVS tube can not be replaced with each other
Clearly the principle we look at some of the parameters of the TVS tube, through the Datasheet look more intuitive

Selection parameters in Figure1 Datasheet
The first column and the second column are related to the specific device.
REVERSE STAND-OFF VOLTAGE (V) reverse peak voltage, which is the working voltage of the TVS tube, to ensure that in normal operation, the resistance of both ends of the TVS tube is very large, which ensures that the TVS tube can absorb the current can be ignored. In general, this value is equal to or slightly greater than the normal operating voltage.
BREAKDOWN VBR (V) MIN & MAX @IT reverse breakdown voltage, indicating that the measured reverse voltage value in the DC current IT conditions, indicating that from the beginning of the device into the reverse avalanche breakdown of the.
TEST CURRENT IT (mA) test current, used to set the device breakdown voltage value.
MAXIMUM CLAMPING @IPP Vc (V) maximum clamping voltage, within the specified pulse duration of tr/tp, the maximum peak current of Ipp is the maximum voltage of the device added to the VOLTAGE.
PEAK CURRENT IPP (A) maximum pulse current, within the specified time tr/tp, the maximum peak pulse current allowed by the device, PULSE.
REVERSE LEAKAGE IR (uA) reverse leakage current, that is, the operating voltage VRWM, the reverse current flowing through the TVS tube @VRWM.
There is:
Cj Junction Capacitance capacitor, mainly refers to the TVS and GND or IO connection, with the capacitance value.
There are also part of the high-speed IO protection on the TVS, will also give insert loss @ Freq. In order to confirm whether it can be used as a protective device.
After learning these parameters, you can choose the right device to use their own circuit, the popular online selection principles.
TVS rated reverse turn off voltage VWM should be greater than or equal to the maximum operating voltage of the protected circuit.
Minimum breakdown voltage VBR=VWM/KBR (among them, KBR=0.8 ~ 0.9).
The TVS maximum clamping voltage should be less than VC protected damage voltage circuit, VC=KC * VBR (including KC=1.3).
The pulse duration within the stipulated time, the maximum peak pulse power PM TVS must be greater than the protected peak pulse power may occur in the circuit. The maximum clamping voltage is determined after the peak pulse current should be greater than the transient surge current.