In addition, the datasheet details the maximum operating voltage that can be continuously withstood without breaking the isolation. The datasheet for a given DC-DC converter typically lists its isolation voltage-the maximum that can be applied for a defined (short) time without current bridging the gap. Because of the separation of input and output circuits, the designer must ensure both circuits have their own ground references. There is an option to connect an isolated DC-DC converter’s floating output to a circuit node on the output side to fix its voltage, which then enables the output to be shifted or inverted relative to another point situated in the output side circuit. While such converters do supply a fixed voltage between the output terminals, they don’t feature a defined or fixed voltage relative to voltage levels in the circuits from which they’ve been isolated (i.e., they are “floating”). (Image source: Digi-Key Electronics)Īnother feature of an isolated DC-DC converter is a floating output. Isolated DC-DC converters are also useful for breaking up ground loops, thus separating parts of a circuit that are sensitive to noise from the sources of that noise (Figure 1).įigure 1: A basic non-isolated DC-DC converter (top) compared with an isolated version (bottom) using a transformer for galvanic isolation. For example, safety requirements may dictate the use of an isolated DC-DC converter-using a transformer (or in some cases coupled inductors) to transfer voltage and current across the gap between the input and output sides-particularly if the input side is connected to voltages that are high enough to endanger humans. But there are many applications that require galvanic isolation (from now on referred to simply as “isolation”) to electrically separate the input and output sides of the device. This reduces complexity, size, and price. In a conventional DC-DC converter, a single regulator circuit allows current to flow directly from input to output.
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The article also describes how the converter’s package meets the need of high-level, automated surface mount assembly, and shows how to design the isolated DC-DC converters into products with minimal voltage and current ripple and reduced electromagnetic interference (EMI). It then introduces example solutions from Murata Electronics and shows how they can be used to achieve isolation without the major design compromises typically associated with transformer-based isolated DC-DC converters. This article explains the circumstances that require the use of isolated DC-DC converters. To address many of these challenges, designers can turn to isolated DC-DC converter modules that have the transformer embedded into the converter’s substrate. The transformer also introduces variability in the DC-DC converter’s performance and makes high-volume automated assembly difficult. Typically, board mounted isolated supplies can be used instead, but these rely upon a transformer to achieve the required electrical isolation, thereby lowering efficiency and increasing the cost, size, and weight of the solution. In the drive to reduce cost and space, monolithic DC-DC converters are a good solution for many high-volume applications, but they can’t be used in designs that require electrical isolation of the power supply input from the output.
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