The new load-dump protection technology could potentially bring 42-volt systems to the fore more quickly because it would prevent damage to on-board electronic vehicle modules. Such modules can be ruined by voltage spikes that occur when battery cables fail or when they are accidentally disconnected. Engineers say that if such voltage spikes go uncontrolled, 42-V automotive systems cannot be brought to production.

The new technology, jointly developed by the University of Michigan-Dearborn and ON Semiconductor (Phoenix), could help solve that problem by accurately controlling the maximum voltages, or so-called "clamp voltages," in MOSFETs and similar power semiconductor devices. Using the new technique, engineers said they can maintain a clamp voltage range of just 4 V — from 52 V to 56 V — in 42-V automotive systems.

In contrast, conventional transient voltage suppression devices, such as rectifiers and metal oxide varistors, offer a clamp voltage range no better than 10 V, and often as much as 20 V. Engineers say that such ranges would be unacceptable for 42-V automotive systems.

"You need a narrower bus voltage range, otherwise it can become a safety issue in the new 42-V systems," said John Shen, co-inventor of the technology and assistant professor of electrical and computer engineering at the University of Michigan-Dearborn. "If the overvoltage rises to a few hundred volts, it could damage the vehicle's electronic modules or ruin its reliability."

The new technique is based on back-to-back polysilicon diode chain technology, sometimes used in conventional power MOSFETs. It differs from conventional MOSFETs, however, in its use of a two-terminal design, which is achieved by internally connecting the circuit's gate and its source. This, in turn, enables it to use innovative, sandwich-type packaging that eliminates wire bonds and allows high current to pass through. Result: Voltage ranges are more precise and packages are less costly.

Engineers at workshop said the key to the technology is its use of the two-terminal design, which departs dramatically from the conventional three-terminal design used in most MOSFETs. Without the two-terminal design, they said, the technology couldn't have used the packaging technique that provides the precise voltage ranges.

"People have used polysilicon diode chains before, but they've never done it in this type of package," Shen said.

The new technique would be used in conjunction with active clamping, and would provide fail-safe protection for safety-critical automotive devices. That's particularly important for automakers as they now approach so-called X-by-wire technologies, which include steer-by-wire, brake-by-wire and throttle-by-wire. Because those systems will have no hydraulic backups, automotive engineers are concerned about providing fail-safe protection for them.

The technology's inventors said that their system would also eliminate the need for hundreds of hours of costly tests that are ordinarily done to see if electronics modules can survive voltage spikes. "If you can guarantee that you can prevent overvoltage, it makes engineers' lives a lot easier," said Randy Frank, manager of technical marketing at ON Semiconductor.

Some engineers at the session questioned whether the technology was necessary, and whether they could achieve the same ends by employing active control algorithms. The technology's inventors, however, said they believe the new technology can provide higher levels of overvoltage protection. "Even with active control algorithms, you can still get a voltage spike," Shen said. "This system provides redundancy against that, which you'll need in drive-by-wire systems."