6, 12, 48 Volts

In the late 70s, my older brother purchased a 1966 Volkswagen Karmann Gia car. This was the sporty two-seater that was produced between 1955 and 1974. This car had the same air-cooled motor as the Volkswagen Beatle. With any older car you spend a lot of time working on it, which he did; not just to get it running but to keep it running. I remember the frustration that he had with the electrical system since the car was based on a 6-volt electrical system, and 6-volt replacement parts such as light bulbs were hard to find for his car which added to his frustration. He thought about converting the car over to 12 volts to reduce his frustration.

Starting in the 1950s the auto industry began to migrate from 6 volts to 12 volts and the main reason was the increase in motor size that required more powerful and higher voltage batteries. Today, the auto industry is going through another voltage migration from 12-volt to dual 12-volt and 48-volt systems. There is a “proposed automotive standard, LV148 that combines a secondary 48 V bus with the existing 12 V system.”1 This standard would supplement the current 12-volt systems.  “… the 12-volt battery that powers all your car’s lights, engine accessories, and infotainment isn’t going anywhere anytime soon.”2 These systems are not hybrids or all electric vehicles that have been out for some time but something new.

These 48-volt systems are used to help provide the ever-growing need for power in cars, lowering emissions and increasing performance in traditional automobiles. A more robust power system that is compatible with both 12-volt and 48-volt rails is needed to make these systems work. The LTC3871 from Power by Linear™ / Analog Devices is a bidirectional buck or boost switching regulator controller that was designed for dual 12-volt and 48-volt automotive systems. The LTC3871 “operates in a buck mode from the 48 V bus to the 12 V bus or in boost mode from 12 V to 48 V.”1 The LTC3871 also provides charging of both batteries or between batteries, as well as pulling power from each battery, converting it as needed by the system.

Typical Applications Block Diagram for the LTC3871 (Image source: Analog Devices)

The future for battery systems in automobiles is the addition of a 48-volt system to the 12-volt system.  That future is now. Today, several automakers such as Audi, Volkswagen, Mercedes-Benz, and Fiat Chrysler Automobiles (FCA) are coming out with production models that use 48-volt systems. My brother sold his Karmann Gia years ago, but I can see him buying a new 48-volt car in the future.



1 – 48V/12V Dual Battery Automotive Systems Require Bi-Directional DC/DC Controllers for Optimum Performance - http://www.analog.com/media/en/technical-documentation/technical-articles/P395_EN-Automotive.pdf

2 – Everything You Need to Know About The Upcoming 48-Volt Electrical Revolution in Cars - https://jalopnik.com/everything-you-need-to-know-about-the-upcoming-48-volt-1790364465

About this author

Image of Stephen Wegscheid Stephen Wegscheid, Senior Product Manager-Semiconductors at Digi-Key Electronics, specializes in analog/linear electronics, connectivity products, and single-board computers. He has a Master of Science degree from Bemidji State University and over 25 years of experience in design, manufacturing, and distribution. Additionally, he is the holder of a US patent.
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