Smart Junction Box (SJB)

Solutions

Smart Junction Boxes have been part of light vehicle electrical systems for decades. Neither methodology for switching and protecting is optimal for today’s cars, trucks, and SUVs with pervasive electronics. SJB options include our eFuse and SmartFET products, which provide state of the art power control and protection in small, lightweight packaging. eFuses champion the protection function, and are positioned close to the battery or to the load, while SmartFETs are optimized for applications in many places in the interior of the car including - but not restricted to - ECMs, BCMs, etc. They are employed in low-side as well as high-side configurations.

eFuses, as the name suggests, mimic the behavior of a mechanical fuse by tripping, entering a current limiting mode, and employing a controlled thermal resistance to shut-down. Additional control and diagnostic features are included in this resettable device. SJBs are ideal solutions for eliminating relays and fuses, as they can reduce wire gauge to lower system cost, while adding accurate protection and diagnostic feedback information. Increasing demands for quality and robustness are addressed by our SmartFETs and eFuses using advanced capabilities to extend device lifetime, and eliminate the need for a human to replace relays or fuses. This increased robustness allows the vehicle manufacturer to create distributed power networks that respond and react instantly to any fault event.

What Are Smart Junction Boxes?

The Smart Junction Box (SJB) is also known as the central body control module. It integrates power distribution controls, fuses, and relays for various vehicle systems in one device. The number of components varies from model to model, but the total can run into the hundreds. That makes troubleshooting difficult, especially if you don’t have a service manual for your particular vehicle model and year.

Originally, SJBs were merely junction boxes that connected the smaller electrical wiring inside your car to larger wiring in the engine bay. The SJB was never meant to be seen or replaced, but things started to get more complex as more functions were added to vehicles, and manufacturers began integrating computers into cars.

Today, SJBs are responsible for many functions, including connecting and distributing electricity, performing diagnostic checks on your vehicle, and displaying alerts. The SJB takes input from various sensors across your car, including temperature and accelerometers. It then interprets this information by comparing it against values stored in its memory and can either raise the alarm or make adjustments to maintain stability.

For example, if the accelerator is depressed, the SJB will receive information from the accelerator pedal position sensor, which controls the throttle position. The SJB then responds by sending a signal to open and to close the throttle plate, allowing more air into the engine and thus creating more power.

It also sends signals to other components such as ignition timing, transmission shifting, fuel injection, and anti-lock braking system to coordinate their actions with each other. In addition to monitoring and controlling these systems, SJBs monitor themselves and send diagnostic trouble codes (DTC) when they detect something out of range or malfunctioning.

What Are eFuses?

With increasing demands on vehicles, makers are looking to electronic fuses (eFuses) to help improve efficiency and much hassle. eFuses provide advantages over traditional fuses due to their high-precision current measurement, enabling better battery charging and discharging control.

An eFuse is a field-programmable device that protects circuits from current overloads and shorts. It can be configured to trip at specific fault levels (current or voltage), thus protecting a circuit from damage caused by too much current flowing through it.

Unlike traditional fuses, eFuses do not require physical replacement when they trip because they reset electronically after a fault has cleared. This saves board space by eliminating the need for spare fuses that may never be needed, as well as the additional space required for physical replacement.

Because eFuses are programmable, engineers can tune them to detect and to respond to specific fault levels with greater precision than mechanical fuses. This enables designers to use smaller eFuses than required if they were using standard mechanical fuses to protect the same circuit or component.