Isolated DC-DC converters reduce application size for noise countermeasure

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

Its new product uses a circuit configuration that delivers stable switching frequency characteristics without needing a photocoupler, reducing application size and workload for noise design countermeasures. Its superior analog design technology enables the BD7Fx05EFJ-C to eradicate the necessity for photocouplers, transformer auxiliary windings, and peripheral components traditionally required to detect secondary-side voltage and current. On top, next to resolving issues with photocouplers, such as large power consumption, fluctuating detection accuracy due to temperature, and deterioration over time, it has also delivered greater miniaturisation by lowering the number of components. Subsequently, it is possible to decrease the number of components – including the photocoupler – utilised for current detection by ten (equivalent to a board area of 30%) compared to general isolated flyback power supply circuits.

The device also has an adaptive ON-time control function that fixes the switching ON time, providing a stable frequency of around 350kHz regardless of output power. To comply with the CISPR25 automotive EMC standard needs significant noise design in the frequency range from 150kHz to 300kHz, but as its new converters do not fall within this band, noise countermeasures may be considerably simplified. This, together with a spread spectrum function that minimises radiated noise, contributes to lowering the number of efforts for noise design.

This new DC-DC converter IC is ideal for gate driver power supplies that must be isolated from the battery for safety, such as automotive electric compressors, PTC heaters, inverters; and industrial power supplies, PLC, and inverters.