Magnetic isolation or traditional approaches?

Galvanic isolation is required in an increasing number of systems and products, especially those that contain high and low voltages and those that operate in electrically noisy environments. Application areas where the need is greatest include industrial, automotive and consumer.

For many years, optocouplers have been a preferred method of galvanic isolation. These devices convert an incoming electrical signal to photons that pass through a non-conductive barrier before being converted back to electrical impulses via a photodetector. The ability to generate photons in proportion to the incoming signal amplitude allows optocouplers to be used for digital and analog circuitry.

As individual devices, optocouplers are small when packaged although when used in multi-channel applications the combined size can become an issue.

Capacitive coupling is an alternative that operates by transferring charge from one plate to another across an isolation boundary that is formed in the capacitor itself. The compact nature of this approach is ideal for multi-channel applications, but the isolation is limited to that of the capacitor.

In theory, inductive coupling offers a good combination of features and is one of the earliest forms of galvanic isolation. However, the transformers can be relatively bulky, limiting the usefulness.

However, advances in semiconductor technology have made it possible to integrate inductors in chip-level products. Devices such as Toshiba’s DCL54x01 comprise a pair of co-packaged chips with one modulating the signal while the other demodulates using on-off-keying that represents a digital signal by the presence (or not) of a carrier signal.

The DCL54x01 has double isolation  that meets the requirements of VDE V 0884-11, protecting against surges as high as 12.8kV. The insulation is expected to remain effective for 70 years based upon measurements and testing.

Toshiba’s white paper on digital isolation for industrial designs can be downloaded here: