48V/12V Dual Battery Automotive Systems Require Bi-Directional DC/DC Controllers : Page 2 of 7

August 16, 2017 //By Bruce Haug, Linear Technology
48V/12V Dual Battery Automotive Systems Require Bi-Directional DC/DC Controllers
Fuel economy requirements and ADAS functions have led to the introduction of a 48V supply bus for cars that coexists with the traditional 12V rail. Both systems are interconnected through bi-directional DC/DC controllers. This article describes the requirements and considerations to optimize the interplay.

Typically, the 12V bus will continue to power the ignition, lighting, infotainment and audio systems. The 48V bus will supply active chassis systems, air conditioning compressors, adjustable suspensions, electric superchargers/turbos and also support regenerative braking. The decision to use an additional 48V bus, which is expected be available across production model ranges soon, can also support starting the engine, which would make stop-start operation smoother. Moreover, the higher voltage means smaller cable cross-sections are needed which reduces cable size and weight. Today's high-end vehicles can have more than 4 kilometers of wiring. Vehicles will become more like PCs, creating the potential for a host of plug-and-play devices. On average, commuters spend 9 percent of their day in an automobile. Thus, introducing multimedia and telematics into vehicles can potentially increase productivity as well as providing additional entertainment.

The key components for autonomous driving include a computer, cameras, radar and LiDAR sensors, all of which require additional energy. This additional energy is required to improve vehicles’ connectivity, not just to the Internet, but to other vehicles and buildings, traffic signals and other structures in the environment. Furthermore, drivetrain components, power steering, oil and water pumps will switch over from mechanical to electrical power.

The future for the 48V battery system is much more near-term than the fully autonomous car, although many automotive suppliers see strong demand for the technological building blocks ultimately needed for self-driving vehicles over the next few years. According to some auto manufactures, a 48V based electrical system results in a 10%-15% gain in fuel economy for internal combustion engine vehicles, thereby reducing CO2 emissions.

Moreover, future vehicles that use a dual 48V/12V system will allow engineers to integrate electrical booster technology that operates independently of the engine load, thereby helping to improve acceleration performance. Already in its advanced development phase, the compressor is placed between the induction system and intercooler and uses 48V to spin-up the turbos.

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