Simplifying surge protection with eFuses

The most commonly applied transient immunity tests are the IEC61000-4-2, the system, ESD, simulates the discharge of a charged human body when it gets connected to an electronic system.

The IEC61000-4-4, the Electrical Fast Transient immunity test simulates the interference caused due to the the inductive switching. The IEC61000-4-5, the Surge Immunity simulates the interference caused due to the atmospheric discharge such as lightning.

So let's compare the power and energy levels of these three test pulses. As shown in the video below, the surge has the highests amount of the pulse power for a longer duration.

The surge pulse has an approximately 100 times higher energy than an EFD pulse train. Due to the high energy content of the surge pulse, the electronic systems can get damaged if appropriate protection circuits are not used. 

The IED defines the test voltage waveform, the range of the test levels, and the test setup and the procedures.

The surge Open Circuit voltage volt waveform has a 1.2 microseconds of rise time, and 50 microseconds of half-wave time, whereas the current profile is defined by 8 microseconds of rise time and 20 microseconds of half-wave time. The surge test also has a several test levels from level 1 to level 4, along with various coupling impedance.

So usually the delegated product standard specifies the specific test conditions. A typical supply bus in a Factory Automation and control requires at least 500V, 2Ω of surge compliance. 

Let us take an example of a PLC CPU model, which is powered from an external field power supply. As this equipment is powered from an external power supply, there is a need of the input protection. So the protection requirements for this end equipment are the input reverse polarity protection, which could happen due to the input side field miswiring, the over voltage protection due to the external field power supply, the over current protection, and the reverse current blocking during the supply voltage interruption test.

Along with this protection requirements, there is also a requirement of protection during the surge test. As this end equipment is powered from an external field power supply, the input ports undergo the IEC test suite.

Lets discuss the surge performance of a TVS Diode, and its implications for the system. Can a TVS, alone, protect the system? Or do we need more protection? What about the surge performance of a TVS diode? 

Consider a typical 24V supply system, with an operating voltage range of 18-36V, a 1.5kHz bi-directional TVS is selected in this example. This shows a positive 500V, 2Ω surge performance on the TVS. As we see here during the surge test, the voltage spikes to the 52V. And then it swings down to negative 52V within a span of 1 microseconds. So the downstream electronics may get damaged due to these over voltage event number 1, and due to the dynamic reverse polarity event during the surge test.

To find out more information, watch the video below.