Noise countermeasures for reducing application size of isolated DC-DC converter

     ROHM has developed an isolated flyback DC-DC converter BD7Fx05EFJ-C (BD7F105EFJ-C, BD7F205EFJ-C) optimized for gate driver power supplies in xEV applications, including electric compressors and PTC heaters. This new DC-DC converter IC is ideal for grid driver power sources that must be isolated from batteries, such as automotive electric compressors, PTC heaters, inverters; And industrial power supplies, PLCS and inverters

     Its new products employ a circuit configuration that provides stable switching frequency characteristics without the need for optical couplers, reducing the application size and noise design effort of countermeasures. Its superior analog design technique allows the BD7Fx05EFJ-C to eliminate the need for optical couplers, transformer auxiliary windings, and peripheral components traditionally used to detect secondary side voltage and current.

     Most importantly, in addition to addressing the problems of the optocoupler, such as high power consumption, fluctuations in detection accuracy due to temperature, and deterioration over time, it also enables greater miniaturization by reducing the number of components. Subsequently, it is possible to reduce the number of components (including optocouplers) used for current detection by 10%(equivalent to 30% of the board area) compared to a typical isolated flyback power circuit. The device also has adaptive ON-time control that can fix the on-switch time and provide a stable frequency of about 350kHz regardless of the output power.

     To comply with CISPR25 automotive EMC standards, significant noise design is required in the frequency range of 150kHz to 300kHz, but since its new converter is not in this band, noise countermeasures may be greatly simplified. This, coupled with the spread spectrum function, minimizes radiated noise and helps reduce noise design effort.