January 15, 2019
| By: Anthony T. Huynh
Principal Member of the Technical Staff, Applications, Industrial Power, Maxim Integrated
In states that experience a lot of lightning strikes—like Florida and Oklahoma—extra care must be taken to prevent this electrical activity from damaging and even shutting down critical industrial equipment. Fortunately, modern protection circuits, which are robust, highly integrated, and easy to implement compared to their predecessors, can help you protect against such faults.
Since all systems are subject to voltage, current, thermal, and other faults, proper protection is critical for system uptime. In the voltage category of faults are incidents like system voltage surge and ringing. In these cases, occurrences such as lightning strikes, a blown fuse, a short circuit, a hot-swap event, or cable ringing can cause the input voltage to go higher and/or lower than the normal DC voltage range. A robust system must either continue to operate throughout the ringing without interruption or at least survive it without damage. On rare occasions, system miswiring occurs, causing input reverse voltage. When the input voltage drops suddenly (input shorted or rings low), the output capacitor is now at a higher potential, causing the reverse voltage condition. Even though they are rare, input reverse voltage faults can cause costly damage to the system.
Current faults include overcurrent or short-circuit faults, inrush current, and reverse current. When the system runs over capacity, this can result in overcurrent loading. A short-circuit can be triggered by a number of events, from a faulty component on the board to accidental drilling into a cable bundle. Left unprotected, the board can become permanently damaged or even catch on fire. Inrush current, if left uncontrolled, can lead to a high current spike that can damage connectors, blow up fuses, and cause voltage ringing on the backplane voltage. Reverse current is another event that can seriously damage the system.
In the thermal category are events such as over-temperature protection and thermal protection. Over-temperature protection shuts down the system to prevent damage or fire problems when the system or component temperature rises to a dangerous level. When a system is properly designed, it should operate without going into over-temperature shutdown mode. Thermal protection is smarter than over-temperature protection. When the temperature is moving higher than normal because of a primary fault, thermal protection warns the system and also provides a choice of ways that the system can dissipate less power. With this capability, the system can attempt to avoid an over-temperature shutdown by reducing its performance until the primary fault has been resolved.
System protection circuitry can help maintain uptime of an automated factory, protecting the equipment against voltage, thermal, current, and other faults.
Keeping Your System Up and Running
There are different system protection techniques available, and it’s good to consider their pros and cons. A discrete or partly integrated IC calls for a lot of external components and the tolerances stack up of the components is tedious to analyze. Newer, more advanced system protection solutions tend to be highly integrated, easy to design-in, and easily able to pass design qualification. In my article, “Understanding System Protection—What You Don’t Know Might Hurt Your System,” I discuss in greater detail various system faults, what to look for in a system protection IC, and the newer system protection technologies available. You can also learn more on the topic by reading the article, “Circle the Wagons: Choose the Right Protection for Your Smart Load.”