Isolated DC/DC converters for xEV

25th January 2023
Sheryl Miles

ROHM has developed an isolated flyback DC/DC converter, BD7Fx05EFJ-C (BD7F105EFJ-C, BD7F205EFJ-C) optimised for gate driver power supplies in xEV applications such as electric compressors, and PTC heaters.

In recent years, xEVs such as hybrid and electric vehicles have become increasingly popular as the industry moves towards achieving a sustainable society. xEVs, which primarily use electricity as their energy source, are equipped with unique applications such as, electric compressors for AC, and PTC heaters to raise the cabin temperature. And as these applications are driven by high voltages, it is necessary to isolate the primary circuit that includes the battery from the secondary circuit comprised of the motor and other systems to ensure safety.

However, in addition to issues such as larger mounting area and power consumption, conventional isolated circuit configurations require considerable noise countermeasures for switching frequencies that vary with output current.

ROHM’s new product utilises a circuit configuration that achieves stable switching frequency characteristics without requiring a photocoupler, decreasing application size together with workload for noise design countermeasure. Leveraging ROHM’s superior analogue design technology allows the BD7Fx05EFJ-C to eliminate the need for photocouplers, transformer auxiliary windings, and peripheral components conventionally necessary to detect secondary-side voltage and current.

On top, next to solving issues with photocouplers, such as large power consumption, fluctuating detection accuracy due to temperature, and deterioration over time, ROHM has also achieved greater miniaturisation by reducing the number of components. As a result, it is possible to reduce the number of components – including the photocoupler – used for current detection by 10 (equivalent to a board area of 30%) compared to general isolated flyback power supply circuits.

The BD7Fx05EFJ-C is also equipped with an adaptive ON-time control function that fixes the switching ON time, ensuring a stable frequency of around 350kHz regardless of output power. To be compliant with the CISPR25 automotive EMC standard requires considerable noise design in the frequency range from 150 to 300kHz, but as ROHM’s new converters do not fall within this band, noise countermeasures can be greatly simplified. This, together with a spread spectrum function that minimises radiated noise, contributes to reducing the number of efforts for noise design.

Going forward, ROHM will continue to develop products that contribute to greater miniaturisation and lower noise by leveraging its strength in analogue technology, helping to achieve a sustainable society.

Product lineup

In addition to reducing the number of components and person-hours required for noise countermeasures, the BD7Fx05EFJ-C improves application reliability by incorporating multiple protection circuits along with a function that stabilizes the output voltage.

Application examples

ROHM’s new DC/DC converter IC is ideal for gate driver power supplies that must be isolated from the battery for safety.
Automotive: electric compressors, PTC heaters, inverters
Industrial: power supplies, PLC (Programable Logic Controller), inverters


Now (in mass production)
Online Distributors: Digi-Key, Mouser, and Farnell
Scheduled for release at other online distributors as well.

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