Automotive buck-boost converter bridges 12V and 48V levels

November 17, 2016 // By Christoph Hammerschmidt
The rapid adoption of 48V hybrid powertrains has driven the demand for power conversion units that allow energy to freely flow between the two voltage levels. The ISL78226 from Intersil is addressing this demand.

The ISL78226 is a six-phase bidirectional PWM controller designed to perform buck and boost power conversions between 12V and 48V automotive buses. With its power conversion efficiency exceeding the 95% mark, a single device delivers up to 3.75 kW and even more in a modular master/slave configuration.

By 2020, automotive 48V systems will help reduce CO2 emissions by up to 15%, improve fuel consumption, capture energy typically lost while braking, and provide torque in the low RPM range for start-stop mild hybrids. The 48V power net is needed to manage the next generation of energy efficient electrical systems that require more power than available with the existing 12V subsystem. To reduce weight, many traditionally mechanical/hydraulic systems such as power steering, roll stabilization, heating, and air conditioning will be converted to 48V electrical drive. A new electric turbocharger will provide on-demand horsepower and torque, enabling the use of smaller more efficient combustion engines without sacrificing drivability. A high power starter/generator will replace the 12V alternator, reducing noise and vibration during engine starting while allowing regenerative braking to recapture up to 4x more of the available kinetic energy. The 12V bus and 12V lead-acid battery will handle the lighter loads, including ignition, interior lighting, navigation and audio systems.

Previously, 48V systems required a DSP with complicated firmware and/or separate buck and boost controllers combined with power stages and complex switching logic. One ISL78226 controller eliminates the complexity associated with previous 48V designs. The controller responds to changing load requirements by automatically adding or dropping phases to maximize system efficiency. It can also manage an abrupt change in power conversion direction. For example, if the 48V starter/generator fails while the vehicle is driving, the ISL78226 DC/DC controller seamlessly reverses power conversion direction so the 12V battery will temporarily supply the 48V subsystems, such as power steering, allowing the vehicle to safely pull over and stop.