Transient suppressor diode parameters and selection problems? Transient voltage suppression diode clamp voltage is not absolutely fixed, with the current changes, the initial turn-on voltage low, when the current reaches the limit value, at both ends of the diode voltage (voltage clamp) reached maximum value.
Selection of transient suppression diode, a breakdown voltage can not be chosen too low, so as not to affect the system‘s normal work, another also to ensure the maximum clamp voltage not exceeds the value of the components in the system voltage limit, in order to avoid the high pressure transient damage to other components. Then it is necessary to estimate the transient high voltage appears to be the maximum transient current value, the choice is greater than this value of the transient suppression diode tube, so as to avoid transient suppression diode tube damage caused by protection failure.
The step of transient suppression diode is as follows:
1 determine the DC voltage or continuous operating voltage of the circuit to be protected. If it is alternating current, the maximum value should be calculated, that is, the effective value of *1.414.
2 transient suppressor diode reverse displacement voltage that is the operating voltage (VRWM) - the choice of transient suppression diode VRWM equal to or greater than the operating voltage specified in step 1. This guarantees under normal working conditions of transient suppression diode absorption current and negligible, if vrwm as specified in step 1 voltage is higher than the transient suppression diodes, transient suppression diode will absorb a large amount of leakage current in the avalanche breakdown state, thus affecting the circuit.
3 maximum peak pulse power: determine the interference pulse of the circuit, according to the interference pulse waveform, pulse duration, can effectively suppress the interference of the transient suppression diode peak pulse power.
4 selected the maximum transient suppression diode clamp voltage (VC) should be less than the maximum allowable voltage of the protected circuit.
5 unipolar or bipolar - bidirectional transient suppression diode for alternating current or from the positive and negative pulse of the occasion. Transient suppression diodes are sometimes used to reduce capacitance. If the circuit has only the positive signal, then the unidirectional transient suppression diode is sufficient. Transient suppression diode mode of operation is as follows: forward surge, transient suppression diode is reverse avalanche breakdown state; reverse surge, transient suppression diodes is similar to a forward biased diode as conduction and surge energy absorption. This is not the case in a low capacitance circuit. Two way transient suppression diodes should be used to protect the low capacitance devices in the circuit from the damage of the reverse surge.
6 if you know more accurate surge current IPP, then you can use VC to determine its power, if you can not determine the scope of power, in general, select the power of some of the better.