DC/DC Converter Design Requirements

Nearly everything would collapse without an electrical power supply. From simple consumer devices to LED lighting, computer networks, the medical devices that help us stay healthy, satellites, or the Hubble telescope that we use to explore distant worlds. And then there are the navigation systems and electric vehicles. Nowadays, ships would find it difficult to reach their port of destination without satellite navigation, and aeroplanes would need an additional navigator. And what about e-mobility? Electric vehicles have to be safe, and now they are even supposed to drive autonomously!

The car is being rethought. There is no longer a steering wheel and we sit in the back seat. Three on-board computers, countless sensors, endless software, and artificial intelligence! And when everything works together and is sufficiently developed, we will rely on the technology, pull down the blinds and arrive relaxed. Fine, this is still a bit in the future, but it already exists for vehicles for the disabled.

The main traction battery powers the engine. All the other consumers, such as the on-board computers with their AI programs, are also powered from the traction battery, but they need lower voltages, such as 12V, 18V, or 24V. The actual microcontrollers and their peripherals operate with 5V, 3.3V, or 1.8V, and these are again derived from the 12V bus. This brings us to the first essential requirement for DC/DC converters: they have to function just as safely and reliably as the entire computer system. And unfortunately, due to physical laws, they also generate heat. And whenever something gets warm (possibly hot), aging occurs. At low temperature increases, this is insignificant, but the hotter the components get, the more pronounced the aging processes become. In the case of electrolytic capacitors, this occurs even disproportionately. With the existing component technology, only good heat dissipation can help.

Fans are usually out of the question, so the only way to dissipate heat is via heat-conducting material, such as a base plate made of aluminium, which transfers the heat directly to the enclosure. There is also a second "trick": instead of using one large DC/DC converter, several smaller converters can be distributed over a larger area—a distributed power architecture. This approach has the added advantage that voltages are generated exactly where they are needed. From a 12V rail—an internal supply bus, so to speak—3.3V is generated directly at the microcontroller, and the analogue circuit for processing sensor signals receives its own 12V/5V converter in close proximity. This architecture is also known as PoL (Point of Load). In addition to improved thermal distribution, it also offers advantages in terms of EMC performance.

Based on what has been said so far, we can already see that the importance of small, highly efficient DC/DC converters is increasing and shaping the architecture of modern electronic devices.

In addition to the requirements already mentioned, the converters must have the smallest possible dimensions and provide a highly constant and accurate output voltage that remains within defined limits even when the load jumps. They must have a wide input voltage range and also be very cost-effective. In most cases, the requirements can practically only be realised with switching regulators because a series regulator would generate too much waste heat. However, a switching regulator requires EMC-compliant filtering at the output and sometimes also at the input. When selecting a converter, it is therefore important to consider which standards it already meets and which additional filters are required.

Converters commonly available on the market range in power from a few hundred milliwatts to several hundred watts. As varied as the power ratings are, so are the typical form factors. These include SMD, SIL, and DIL packages for power levels up to approximately 10W, inch-sized modules for power levels up to around 40W, and brick-style converters for higher power applications. A standard full brick DC/DC converter measures 117mm x 61mm.

The high efficiency of the RPX-4.0 allows operation at full power up to 65°C and with power reduction up to 90°C depending on the variant and mounting arrangement. The efficiency curve rises for low output powers, i.e. the converter can also be used advantageously for medium and low output powers. This is achieved, among other things, by intelligent control of the switching frequency and an integrated and shielded storage choke, which additionally provides for low EMI.


The design follows RECOM's '3D Power Packaging®' technology for high power density and uses a flip-chip on leadframe construction. It comes with a 3-year RECOM warranty. An RPX-4.0-EVM-1 evaluation board is also available to allow customers to test all product features and optimize filtering to meet target system requirements.

If LEDs are powered from a voltage source, they require a series resistor for current limitation and operating point adjustment. Significant power loss occurs in this resistor. This loss can be avoided by using a current source to drive the LED. With a voltage regulator and an operational amplifier, a simple circuit can be realised that exhibits current source characteristics with respect to the LED:

With RECOM's 3DPP^® technology, the RPX-4.0 has a significantly higher power density than conventional converters, as shown in these comparative images, all at the same scale. Despite its incredibly small size, the excellent internal thermal management design still allows full load operation without forced cooling.