TVS tubes have unidirectional and bidirectional points (the letter behind the one-way model is "A", the bidirectional is "CA"), the characteristics of one-way TVS tubes are similar to the voltage regulator diode, and the characteristics of two-way TVS tubes are equivalent to two voltage regulator diodes in series. Its main characteristic parameters are:

① Reverse off-state voltage (cut-off voltage)VRWM and reverse leakage current IR: reverse off-state voltage (cut-off voltage)VRWM indicates the highest voltage that the TVS tube is not on, and there is only a small reverse leakage current IR at this voltage.

(2) Breakdown voltage VBR: TVS tube through the specified test current IT voltage, which is a sign of TVS tube conduction voltage (P4KE, P6KE, 1.5KE series models in the number is the nominal value of the breakdown voltage, other series of numbers are reverse off-state voltage value). TVS tube breakdown voltage has an error range of ±5% (±10% without "A").

(3) Pulse peak current IPP: TVS tube allows 10/1000μs wave through the largest peak current (8/20μs wave peak current is about 5 times), more than this current value may cause long-term damage. In the same series, the higher the breakdown voltage, the lower the peak current allowed through the tube.

④* Large clamping voltage VC: the voltage at both ends of the TVS tube when it flows through the pulse peak current IPP.

⑤ Pulse peak power Pm: pulse peak power Pm refers to the product of 10/1000μs wave pulse peak current IPP and the largest clamping voltage VC, that is, Pm=IPP*VC.

⑥ Steady state power P0: TVS tube can also be used as a voltage regulator diode, at this time to use steady state power. The steady state power of each series is shown in the following table:

Peak pulse power Pm 400W 500W 600W 1500W 3000W

Steady state power P0 1W 3W 5W 6.5W 8W

7 Inter-electrode capacitance Cj: Like varistor, the inter-electrode capacitance Cj of TVS tube is also larger, and the unidirectional is larger than the bidirectional, and the larger the power is, the larger the capacitance is.

3, the use of guidance:

When TVS tube is used, it is generally in parallel on the protected circuit. In order to limit the current flowing through the TVS tube to not exceed the peak current IPP allowed through the tube, the current limiting elements should be connected in series on the line, such as resistors, self-restoring fuses, inductors, etc.

② Selection of breakdown voltage VBR: The breakdown voltage of TVS tube should be selected according to the formula: VBRmin≥ 1.2UM or VRWM ≥ 1.1UM according to the line * high operating voltage UM.

③ Selection of pulse peak current IPP and maximum clamping voltage VC: When TVS tube is used alone, it is necessary to select the appropriate IPP model according to the maximum inrush current that may occur on the line. When the TVS tube is used as the second level of protection, it is generally OK to use 500W ~ 600W. It should be noted that the maximum clamping voltage VC at this time should not be greater than the maximum surge voltage (safety voltage) that the protected device can withstand.

When used for signal transmission circuit protection, be sure to pay attention to the frequency or transmission rate of the transmitted signal. When the signal frequency (transmission rate) is ≥10MHz (Mb/s), Cj should be ≤60pF; When the signal frequency (transmission rate) is greater than or equal to 100MHz (Mb/s), Cj should be less than or equal to 20pF. When the signal frequency or transmission rate is high, the pipe of low capacitance series should be selected. When the low capacitance series still cannot meet the requirements, the TVS tube should be connected to the bridge composed of a fast recovery diode to reduce the total equivalent capacitance and increase the transmission signal frequency. * High transmission frequency up to 20MHz.