48V/12V Dual Battery Automotive Systems Require Bi-Directional DC/DC Controllers

August 16, 2017 // By Bruce Haug, Linear Technology
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.

With fuel economy regulations tightening and autonomous-driving capability with connectivity proliferating, the old-fashioned 12-volt automotive electrical system has reached its usable power limit. Furthermore, a vast increase in automotive electronic systems, coupled with related demands on power, has created an array of new engineering opportunities and challenges. As a result, the 12V lead-acid battery automotive system with its 3kW power limit has been supplemented.

A newly proposed automotive standard, LV148, combines a secondary 48V bus with the existing 12V system. The 48V rail includes an integrated starter generator (ISG) or belt start generator, a 48V lithium-ion battery and a bi-directional DC/DC converter for delivery of up to 10kW of available energy from the 48V and 12V batteries combined. This technology is targeted at conventional internal combustion automobiles, as well as hybrid electric and mild hybrid vehicles, as auto manufacturers strive to meet increasingly stringent CO2 emissions targets.

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