纳秒脉冲下典型钳压型浪涌防护元件的响应特性

Nanosecond pulse response of typical voltage-clamping surge protective devices

为研究以压敏电阻和瞬态抑制(TVS)二极管为代表的典型钳压型浪涌防护元件的纳秒脉冲响应特性,为电磁脉冲干扰防护元件的选型提供科学依据,分别基于百ns和2ns上升前沿电磁脉冲直接注入的方式,实验测试并对比分析两类元件在不同脉冲上升沿时间、电压幅值等情况下的响应差异,并阐明产生过冲响应差异的物理机理。结果表明:两类防护元件的响应时间均与注入纳秒脉冲上升沿时间有关,且随着上升沿的增加而变长,其中TVS二极管在相同上升脉冲情况下具有更为敏感的响应速度;当注入脉冲电压幅值增加时,PN结热积累加快,击穿速度加快,元件响应时间更短,相比于TVS稳定的钳位幅值,压敏电阻在钳位幅值附近处振荡明显;当快速脉冲到达时,压敏电阻和TVS二极管响应曲线在钳位幅值稳定前均发生过冲现象,并且两类防护元件的过冲电压均随着注入脉冲幅值的增加而增加;尽管钳位电压幅值由自身防护特性决定,但在相同注入脉冲条件下,同类不同型号的防护元件过冲电压几乎相同,通常压敏电阻过冲电压小于钳位电压,而TVS二极管则相反,并且随着钳位幅值变小,过冲电压与钳位电压的比值变大,这意味着过冲现象对低压TVS二极管性能影响更为严重。

Varistors and transient voltage suppressor （TVS） diodes, as two typical surge protective devices, are often used to limit voltage in the high power microwave pulse. To investigate their nanosecond pulse response and provide a scientific basis for the selection of electromagnetic pulse interference protection devices, the experimental measurement were carried out by the way of hundreds of nanoseconds and two nanoseconds risetime pulses injecting directly. Moreover, the differences of overshoot re- sponse between the varistors and TVS diodes, under different conditions of risetime and voltage amplitudes, are developed by comparative analyses, and the physical mechanism is also expatiated. The results demonstrate that the response time of both devices depend on the risetime of the injected nanosecond pulse and it increases with the increase of pulse risetime, and TVS diode has the more faster response speed for the same risetime pulses. As the amplitude of injected pulse voltage increases, the thermal accumulation in P-N junction and the breakdown speed increases, which results in a shorter response time. Furthermore, the limited voltage amplitude of varistor is a more drastic oscillation than that of TVS diode. The voltage overshoot phenomenon, in addition, is appearing before the limited voltage stability for both surge protective devices when the fast pulses being injected. The amplitude of overshoot for two typical surge protective devices increases with the injected pulse amplitude increasing, although the limited voltage amplitude is usually determined by its own protective characteristics, the overshoot voltages for different models of one kind of device have nearly the identical amplitude under the same injected pulse. Furthermore, the overshoot voltage of varistor is usually lower than its limited voltage. For TVS diodes, however, the overshoot voltage is higher than its limited voltage and the ratio of the former to the latter increases with the decrease of the limited voltage amplitude, which means that the voltage overshoot phenomenon has a more serious impact on the performance of the low-voltage TVS diode.