Implementing digital isolation in an industrial PLC

Many industrial applications require some form of galvanic isolation due to the range of voltages present as well as the electrical noise and spikes that can interfere with system operation.

There are multiple techniques available for providing galvanic isolation including optical, capacitive and magnetic coupling.

While individual optocoupler devices are small, multi-channel solutions can become bulky. Capacitive coupling is smaller but relies on the capacitor itself for isolation which can mean that some spikes are able to traverse the isolation gap. The magnetic approach was one of the earliest approaches but with transformers the solution is often bulky.

Advances in semiconductor technology have made it possible to integrate inductors into smaller chip-level packaging. Devices such as Toshiba’s DCL54x01 use this approach and comprise two co-packaged chips with one acting as a modulator and the other as a demodulator.

A double-isolation structure comprising two insulation layers ensures safe operation, even in the most extreme conditions.

In the industrial world, PLCs are commonly used, and each installation requires isolation for safe and reliable operation. Adding to the challenge, many PLCs now operate at higher frequencies than before.

The power module requires isolation for PWM control lines and signal lines used for monitoring operation. Multiple PWM signals may be required to avoid switching issues such as shoot-through, thereby increasing the need for parallel isolation channels.

Additionally, error signals returning to the controller will require reverse-direction capabilities in the isolation device. Other areas of the PLC including modules for motor control, analog input and digital I/O will also require isolation.

Toshiba’s highly flexible and capable DCL54x01 ensures the availability of industrial-strength, multi-channel isolation in a compact footprint.

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