Theme: 48v automated Power Supply Sources. Plan 48 volt: what it is and why it’s important

The shift to hybrids

The first step towards hybridisation is to use 48V systems to help run internal combustion engines more efficiently, by driving auxiliary functions such as power steering racks, brake vacuum pumps and water pumps with electric motors rather than using a power take-off from the engine. This can be more energy efficient than mechanical drive, since the operation of these functions can be more closely matched to the vehicle’s needs. For example, intermittent electrical drive is more efficient than continuous mechanical drive for running vehicle air conditioning, because an AC system’s compressor is off more often than it is on.

The next step is a ’mild hybrid’, which replaces a car’s traditional starter motor with a motor generator unit (also known as a belt-driven starter generator). This acts as generator under braking, recharging the vehicle’s battery. When the vehicle comes to a stop, the motor generator, driven by AC power provided though an inverter from the battery, can restart the internal combustion engine and set the vehicle moving again more quickly by providing additional torque. Industry estimates say this approach can improve fuel economy by 10 to 20% at a much lower cost than a full hybrid approach.

Using a slightly more powerful motor generator will enable a car to creep through a parking lot or a city’s low-emission zone on electric power, reducing fuel consumption and emissions. More complex hybrids use much more powerful motors to handle traction at normal road speeds. They also use the electric motor to smooth out torque delivery from the internal combustion engine, when changing gears or pulling away from a stop, and to provide additional power as necessary. These two strategies help keep the engine operating at its peak efficiency, reducing emissions and making the vehicle more responsive and fun to drive.

Making the transition

The industry has too much invested in 12V electrical systems to try to make an overnight transition to 48V. Instead, the shift to 48V will come gradually, with the introduction of 48V infrastructure to run alongside the ‘legacy’ 12V system. A generic 48V system is likely to include a 48V battery and battery controller, the motor generator unit and inverter, power bus and connection points, as well as a DC/DC converter to transfer power between the two systems as needed.

Shifting to 48V will demand the development of a wide range of new componentry that can operate at this higher voltage and meet the demanding standards of the automotive industry. For example, mild hybrids will need efficient inverter circuits to be able to contribute energy to, and draw energy from, the onboard 48V battery without excessive losses. Wiring looms may have to be upgraded to handle the higher voltages and currents, as will any devices that are switching significant amounts of power at 48V.

We’ve already talked about using electric power to fill gaps in an internal combustion engine’s power curve, or just to provide a boost. In most cases the energy for this will be drawn from a battery, but there is an alternative approach: a super-capacitor. Eaton offers an XLR 48V super-capacitor module (right) designed for high power, frequent charge/discharge systems in hybrid or electric vehicles, public transportation, and related applications. Eaton argues that adding such a model to a hybrid can reduce battery size and weight or even replace batteries altogether in some cases. The 166F, 5milliohm module is made up of 18 supercapacitor cells, and includes cell-voltage management circuitry and an over-voltage alarm. It’s sealed to IP65, making it suitable for use in dusty areas and where it will be jet washed.

You should also expect rapid development in power electronics to serve the opportunity created by the shift to 48V systems.

One key area will be charging control and battery management. Companies such as NXP are already producing relevant battery-management devices, such as the MC33771B Li-ion battery manager for up to 14 battery cells with built-in current balancing.

Efficient DC/DC conversion is also important. ON Semiconductor has developed highly integrated modules, such as its FTCO3V85A, an 80V, low Rds(on) automotive-qualified power module featuring a three-phase MOSFET module, for use in 48V DC/DC conversion.

Vendors are also exploring multiple approaches to partitioning key components of the drivetrain. For example, STMicroelectronics offers the L9907, a smart-power FET driver for three-phase brushless DC motors. It is built in the company’s BCD-6s process and can control six pre-driver channels independently, enabling a variety of motor control strategies for three-phase brushless DC motors.

Elmos has taken a different approach with its E523.52, a programmable, high-voltage brushless motor controller for 24V and 48V vehicles. It has three half-bridge drivers, an 11V DC/DC step-down converter, two linear regulators, and a 16bit microcontroller. The 11V output can power six gate drivers, internal linear regulators, and external loads such as external Hall sensors.

Lower down the integration chain, companies such as Infineon and ON Semiconductor are working on power transistors optimised for 48V automotive applications. Infineon is using its OptiMOS 80V/100V trench technology and leadless TOLL or TOLG packages to build basic devices for 48V applications. ON Semiconductor is introducing a family of very low resistance 80V N-channel PowerTrench MOSFETs in a compact TOLL package, which it says are a good fit for high-current 48V applications.

The increased currents and voltages used in 48V systems will inevitably lead to a more electrically noisy environment. Some manufacturers are already working on ways to counter this problem. For example, Panasonic’s EEH-ZE series hybrid aluminium electrolytic capacitors (left) have been designed for use in filtering the inputs and outputs of power converters and voltage regulators, for power and battery decoupling, and in a variety of automotive applications. The parts are surface-mountable and comply with AEC-Q200.

Yageo makes two ranges of multilayer ceramic capacitors for the automotive market. The AC series, NP0/X7R parts are available with working voltages ranging from 6.3V to 630V, and at capacitances ranging from 0.2pF to 2.2mF. They’re designed for a range of automotive applications, including entertainment, comfort, security and infotainment. Importantly, the parts are free of lead and halogens, comply with RoHS requirements, and meet the AEC-Q200 automotive quality standard.

The AS series parts are available in capacitances from 1nF to 4.7uF, and with operating voltages from 10V to 250V. They have similar applications, environmental and quality characteristics to the AC series parts, but have soft terminations made up of multiple layers of plating. The soft terminations act as a form of strain relief, making the parts less likely to crack if the board to which they are soldered is flexed.

The shift to e-mobility is also creating demand for new forms of passives. TDK’s CeraLink capacitors are designed to act as ripple-current suppressors, DC link capacitors, and snubbers in the own generation of fast-switching automotive power supplies and inverters made possible by the availability of new IGBTs and MOSFETs, where low equivalent series resistances and inductances are important.

HIGH-EFFICIENCY BOOST CONVERTER PROVIDES 48V FOR IP PHONES

IP phones require that data and power on the same cable. A high voltage power source of 48V is required, to reduce the voltage drop in the cable.



This application note describes a DC-DC step-up converter that can deliver the required 48V supply, from the 12V source typically available in the host of such systems.

It delivers low-voltage ripple, essential to prevent data errors.
Isolation is provided by the 12V power-supply. For a system with one or two ports, a custom-designed DC-DC converter is more suitable than power modules, or "bricks", since bricks tend to be bulkier and are more expensive. They are more suitable for systems that support more ports, where the power demand is higher.
The MAX668 is an excellent choice for the design of a DC-DC step-up converter. The MAX668, a current-mode controller, operates in the PWM mode at medium and heavy loads, providing high-efficiency and low-noise. With power levels greater than 20W, efficiencies of more than 90% are achievable.



The circuit of