TVS diode selection procedures and type selection should pay attention to the problem
A maximum of TVS diodes are used in the electronic protection devices, while the TVS tube is a kind of overvoltage device. TVS diode is widely used in semiconductor and sensitive devices, and is usually used for the protection of the two stage of electronic products. TVS will be used for basic diode after discharge in ceramic gas protection of two, but there are users directly from the level of protection for products. The characteristics of fast response (PS), TVS tube has the advantages of small size, big pulse power, clamping voltage is low and so on. TVS tube of its 10/1000 S wave pulse power from 400W to 30KW, the pulse peak current from 0.52A to 544A; breakdown voltage from 6.8V to 550V series of values, easy to use a variety of different voltage circuit. So TVS diode specific how to choose it? In this small series of electronic technology to summarize the following points:
A, TVS diode selection steps are as follows:
1 to determine the DC voltage of the circuit to be protected or continuous operating voltage, if it is alternating current, the maximum value should be calculated, that is, the effective value of *1.414.
The reverse displacement voltage of the 2.TVS tube, namely the working voltage (VRWM), selects the VRWM equal to or greater than the operating voltage specified in the step 1. This ensures negligible current in the normal working conditions of TVS diode absorption, if the voltage specified in step 1 is higher than that of TVS diode VRWM, TVS diode will absorb large amounts of leakage currents in avalanche breakdown state, thus affecting the circuit work.
3 maximum peak pulse power: determine the interference pulse of the circuit, according to the interference pulse waveform, pulse duration, can effectively inhibit the interference of the TVS diode peak pulse power.
4 selected TVS diode maximum clamp voltage (VC) should be less than the maximum allowable voltage of the protected circuit.
5 unipolar or bipolar - there is often such a misunderstanding that the bi-directional TVS diode used to suppress the reverse surge pulse, in fact, it is not the case. Bidirectional TVS diode for alternating current or positive and negative pulse. TVS diodes are sometimes used to reduce capacitance. If the circuit has only a positive signal, then one way TVS diode is sufficient. TVS diode operation is as follows: forward surge, TVS diode in reverse avalanche breakdown state; reverse surge, TVS diodes are similar to the forward bias diode and absorb surge energy. This is not the case in a low capacitance circuit. Two way TVS diodes should be used to protect the low capacitance devices in the circuit from the damage of the reverse surge.
6 for example, know more accurate surge current IPP, then you can use VC to determine its power, if you can not determine the scope of power, for the TVS type selection in general, select the power of some of the better.
Two, TVS diode selection should pay attention to the following issues:
The maximum safe voltage clamp voltage is less than the maximum allowed VC circuit.
The cut-off voltage of VRWM is greater than the maximum operating voltage of the circuit, the general can choose VRWM is equal to or slightly greater than the maximum operating voltage of the circuit.
Rated maximum pulse power (given in the TVS diode parameters) PM is greater than the maximum transient surge power.