What Is a DC-to-DC Converter?

DC-to-DC converters are devices that temporarily store electrical energy for the purpose of converting direct current (DC) from one voltage level to another. In automotive applications, they are an essential intermediary between systems of different voltage levels throughout the vehicle.

Control circuitry played the role of DC-to-DC converter in the traditional 12V electrical architecture that dominated the automotive industry starting in the 1950s. Over the decades, new features and innovations increased the complexity of vehicle electrical/electronic architectures, including the introduction of cruise control in the 1950s, emission control features in the ’70s and electrical centers in the ’90s. DC-to-DC converters enabled this growth by stepping down power from the 12V battery to lower-voltage electrical systems such as the instrumentation panel, entertainment system, LED lighting and sensors (which can require as little as 3.3V). These low-voltage DC-to-DC converters are still an essential part of the control circuitry in all vehicles today — both in internal combustion engine vehicles and battery electric vehicles (BEVs).

BEVs introduce a much greater level of electrical power, requiring a more robust DC-to-DC converter. Systems higher than 60V are considered high voltage; typical BEV batteries range from 400V to 800V. The voltage has to step down to, say, 48V to power an air conditioning unit, and down to 12V and lower to power numerous electronics throughout the vehicle. The voltage may also have to be stepped up — for example, if a battery running at 400V is connected to a charging station running at 800V.

The expansion of software-enabled features, including active safety, connectivity and infotainment, has only added to the complexity of the low-voltage architecture. BEVs must deliver enough power to drive the wheels of the car while also being able to step down current to run all of the low-voltage devices that make up the software-defined vehicle. And they need to be reliable enough to meet the functional safety demands of autonomous driving features and advanced driver-assistance systems.

DC-to-DC converters for high-voltage applications

High-voltage DC-to-DC converters are much larger and heavier than their low-voltage counterparts due to the extra shielding required to protect nearby components from the electromagnetic interference generated from increased current. Because EV designers are looking to reduce size and weight wherever possible to extend the vehicles’ range, they are turning to DC-to-DC converters with a higher power density, as measured in kilowatts of power per unit of volume.

To step 400V or 800V down to 12V requires a DC-to-DC converter with power ranging from 700W to 4kW — or even up to 12kW for a commercial vehicle.

The challenge is to optimize for space while maintaining the highest levels of safety and efficiency possible. While some automakers have retained a 12V battery in addition to the main 400V or 800V battery, emerging designs are achieving greater efficiencies by combining the larger battery with a more sophisticated DC-to-DC converter, thereby eliminating the weight, cost and maintenance of a separate 12V battery.

The software that runs the DC-to-DC converter is key to ensuring that conversion remains efficient, and knowledge of the entire vehicle architecture informs the software and hardware design. While high-voltage vehicle components are relatively new territory for the industry, Aptiv is building on decades of knowledge about what OEMs need to lead the way in vehicle electrification solutions. The feature-rich software-defined vehicles of tomorrow must be space- and energy-efficient enough to enable the functions that OEMs and consumers expect, like over-the-air updates, cybersecurity, autonomous driving, advanced safety and state-of-the-art user experiences.   

Aptiv’s expertise with both the brain and the nervous system of the vehicle enables us to optimize electrical/electronic systems and packaging space while still fulfilling the performance, functional safety, and compute and power needs.