TND6335/D
Rev. 2, August − 2021

Ask the Expert: 48−Volt AutomotiveElectrical Systems Emerging© Semiconductor Components Industries, LLC, 2020

August, 2021 − Rev. 2

1Publication Order Number:
TND6335/D

Ask the Expert: 48−Volt Automotive Electrical Systems
Emerging
Introduction
Ever since the auto manufacturers switched from a 6−volt battery to a 12−volt battery in themid 1950’s, they have continued to add more electrical and electronic equipment. All of these
new accessories have stretched most 12−volt vehicle electrical systems to their limit. The
industry is responding by developing a new, improved electrical system using a 48−volt battery.
The more powerful 48−volt systems are first showing up on new vehicles called “mild hybrids.”
Mild hybrid electrical vehicles (MHEVs) use a small internal combustion engine (ICE) and an
AC synchronous induction motor to power the vehicle. The discussion here relates to those mildhybrid vehicles.

Figure 1. Jay Nagle
Senior Engineer for the Power Solutions Group Division, onsemi

www.onsemi.com
2Q. What factors are actually driving the development and adoption of these mildhybrids?
A. The primary driving force is the increasingly stringent government regulations that dictate thereduction of CO2 emissions, improvement in gas mileage, and making the vehicle moreenvironmentally friendly. The Americas, Asia, and Europe are all working toward new rules andregulations. The European region has the most aggressive reduction target compared to theAmericas and Asia regions. One solution has been the development of the mild hybrid vehicle
with its small ICE and a strong electric motor.
Q. Can a 48−volt battery really deliver enough power to run a MHEV?
A. No, the 48−volt battery cannot propel the car on its own. Its main function is to power theelectric motor, or electric machine as it is also called, and give the ICE a boost when starting
off. The extra torque makes the vehicle feel like it’s a larger, more powerful vehicle. To clarify,
there are several different MHEV topologies that are based upon the physical location andconnection of the electric machine to the vehicle drive train. These are designated P0 throughP4. The P0 configuration has the electric machine connected to the ICE by belt.
The P1 architecture puts the electric machine directly on the crankshaft of the ICE. The P2
through P4 arrangements involve more complex gearing connections. The P0 and P1
arrangements are the most common but do not provide full driving capability with the 48 V
battery alone. Then the S/G automatically restarts the ICE when the accelerator is pressed.
While some gas mileage savings will accrue, the primary objective of the mild hybrid vehicle isto provide an additional 4%−10% reduction in CO2 emissions compared to traditional ICEvehicles.
Infotainment
12 V LoadsLeadAcidLighting
Networks12 V

Body Electrical (Windows,Doors, Seats, ETC)
MCU

Bidirectional
DC−DCICE
Motor/Starter/−Generator

Inverter
Lithium
ION

48 VHVAC
48 V Loads

Pumps
Suspension

32−Bit MCU
MonitorControl

Turbo

This simplified diagram shows the dual 12/48−volt electrical system in mild hybrid vehicles.

Figure 2. 12/48−Volt Electrical System

www.onsemi.com
3

Q. What does the electrical system of a mild hybrid with its 48−volt battery look like?
A. A simplified diagram of that electrical system is shown in Figure 2. It consists of two powerbuses, a 12−volt battery and bus to power most of the traditional auto loads, and a 48−volt
battery and bus to power the electric drive motor and other higher power accessories. The
12−volt system operates all the usual equipment including the infotainment system, lighting,and body electrical accessories such as windows, doors, seats, etc. The 48−volt system
operates the electrical drive motor and any heavy−duty loads such as HVAC, selected pumps,
steering, and suspensions systems — and an electric turbocharger if the ICE uses one.
The two major electrical systems are connected to a bidirectional buck−boost DC−DC
converter that serves both the 12− and 48−volt buses and an inverter to operate the 3 phase
PM synchronous induction drive motor. Some S/Gs are belt driven, while other manufacturers
are placing the S/G between the engine and transmission.
Q. When will we begin seeing the mild hybrids with their 48−volt systems?
A. Some vehicles with 48−volt systems are already available. For example, Mercedes and Audi
offer cars, and Fiat Chrysler offers the 1500 RAM pickup with a mild hybrid system. Volkswagenwill have vehicles soon. Between now and 2025, the number of mild hybrids is expected to growat least 30% per year and eventually becoming about 10% of the total vehicle market. Industry
has determined that the mild hybrid is a good balance between complying with the new tougher
emission standards and providing reasonable cost and performance.
Q. How are the batteries usually charged?
A. In the mild hybrid, the 48−volt battery is charged by a belt−driven S/G driven by the ICE or
the integrated starter generator. Some charging also occurs during deceleration, regenerative
braking, and coasting. The 12−volt battery gets charged by the 48−volt battery via a DC−DCconverter. The 12−volt battery can also recharge the 48−volt battery, if required. A mild hybrid
is not like a plug−in hybrid vehicle (PHEV) that contains an onboard charger (OBC) andconnects directly to the AC line source at home or some convenient charging station torecharge.
Q. What are some of the main electronic components and circuits in this new system?
A. The primary electronic units in the 48−volt system are a three−phase inverter to operate themotor/ starter/generator and the DC−DC converter that ties the 12− and 48−volt systems
together. A major control center with 32−bit MCU oversees the whole system. It takes inputs
from various sensors around the vehicle and provides the outputs that enable the system.

www.onsemi.com
4

Q. What are some of the products that onsemi offers to address this new system?
A. onsemi has a broad automotive portfolio that can provide complete system solutions for
48−volt MHEV systems. The central component is the fast discrete silicon power MOSFET. Theonsemi MOSFET portfolio offers low resistance, low inductance devices in small, cost−efficient
packages that help to minimize switching and conduction losses.
This translates into high−efficiency operation of both the inverter and the 48− to 12−voltbi−directional converter in the 48−volt system with lower system costs. These best−in−classdevices are complemented with matching gate drivers.
onsemi’s Automotive Power Modules (APMs) are complete pre−wired one−half or
three−phase bridge circuits that make it easy to build an inverter for the S/G or any 48−volt motorin the system. The primary benefits of using an onsemi APM module in a 48−volt system is thatthese integrated modules with their compact footprint and high−power density have the ability
to deliver high power when needed. This translates to cost and weight savings essential for CO2
emissions reduction.
Additional solutions offered in onsemi’s portfolio to provide the “one stop shopping” are:
• A new product line of operational amplifiers optimized for current sensing in the main drive
motor and other critical circuits• High−speed digital isolators• Gate Drivers• High−efficiency DC/DC converters• Transceivers for CAN, LIN, and Flex Ray communications• ESD/EMI protection components• eFuse, a protective device that connects between the 48−volt battery and the inverter

www.onsemi.com
5Why 48 Volts?
Many have wondered why 48 volts was selected as the new vehicle power source. First, it
provides a significant boost in power over a 12−volt system. While a standard 12−volt system
can put out a maximum of 2 to 4 kW, the 48−volt system can deliver up to 10 − 20 kW. The higher
voltage does a better job of operating heavy−duty devices like pumps, compressors, turbos, andsuspension components.
A good source of 48 volts is a lithium ion battery. Higher voltages reduce current levels for agiven amount of power consumption. Less current means that smaller wiring can be used toreduce the size and weight of the vehicle wiring harnesses.
Finally, that level of voltage falls right below the threshold of human shock. Most individuals
do not feel electrical shock from voltages below 50 to 60 volts. That makes the 48−volt systems
generally safe for humans to operate, service, or troubleshoot.

onsemi,, and other names, marks, and brands are registered and/or common law trademarks of Semiconductor Components Industries, LLC dba “onsemi” or its affiliates
and/or subsidiaries in the United States and/or other countries. onsemi owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property.
A listing of onsemi’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. onsemi reserves the right to make changes at any time to any
products or information herein, without notice. The information herein is provided “as−is” and onsemi makes no warranty, representation or guarantee regarding the accuracy of theinformation, product features, availability, functionality, or suitability of its products for any particular purpose, nor does onsemi assume any liability arising out of the application or useof any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Buyer is responsible for its products
and applications using onsemi products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information
provided by onsemi. “Typical” parameters which may be provided in onsemi data sheets and/or specifications can and do vary in different applications and actual performance mayvary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. onsemi does not convey any licenseunder any of its intellectual property rights nor the rights of others. onsemi products are not designed, intended, or authorized for use as a critical component in life support systems
or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should
Buyer purchase or use onsemi products for any such unintended or unauthorized application, Buyer shall indemnify and hold onsemi and its officers, employees, subsidiaries, affiliates,and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or deathassociated with such unintended or unauthorized use, even if such claim alleges that onsemi was negligent regarding the design or manufacture of the part. onsemi is an Equal
Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.

PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT:
Email Requests to: orderlit@onsemi.com
onsemi Website: www.onsemi.com◊

TECHNICAL SUPPORTNorth American Technical Support:
Voice Mail: 1 800−282−9855 Toll Free USA/Canada
Phone: 011 421 33 790 2910

www.onsemi.com
6Europe, Middle East and Africa Technical Support:
Phone: 00421 33 790 2910
For additional information, please contact your local Sales Representative