Optocoupler Replacement with Digital Isolators
Octocouplers

Optocoupler Replacement with Digital Isolators

Twenty years ago, members of RDI’s engineering staff participated in an electronics revolution that would forever change the form and function of one of the world’s most successful electronic components…the Optocoupler.

Optocoupler replacement with digital isolators is now very common and we’re offering that knowledge to customers who seek the advantages of eliminating optos from their applications but lack the experience required to design them out and get UL or IEC approval.

In this note you’ll discover:

  • Why and when you should replace optocouplers with digital isolators
  • Digital Isolator basics
  • RDI’s expertise in digital isolator design, applications and regulatory management

Optocoupler and Schematic

Octocouplers

Optocouplers, or optos as they are typically known provide a high voltage isolation barrier between two points on an electronic circuit.

The input signal powers a light emitting diode (LED) which is optically connected via a light pipe to a light sensitive transistor. When the light shines, the output transistor is switched on, connecting the two nodes functionally but with galvanic isolation, or zero current flow.

Digital Isolator History

In 1998 a company called Non-Volatile Electronics (NVE) in Minnesota pioneered practical use of a quantum magnetic effect known as Giant Magnetoristance (GMR) to sense very small magnetic fields on a semiconductor chip. One of our engineers was part of the NVE design team who added switching electronics, an insulating layer and a simple coil to the chip to create the world’s first monolithic digital isolator and in the process, sound the death knell of the optocoupler in digital applications.

Since then, GMR isolator technology has been followed by capacitive and inductive isolators using the same vertical chip design with an electronic base layer, a high voltage insulator, and a passive device to provide a current or voltage from the input that can be sensed at the output on the other side of the isolator. The technology is catching on; more than two billion channels of digital isolators have been sold in the past decade.

Advantages of Digital Isolators

Digital Isolators provide tremendous advantages over optocouplers, especially in their cost per channel. A standard 5kV opto occupies the same circuit board space as a 4-channel digital isolator of the same rated voltage and costs the same to manufacture. Moreover, the data rate, pulse width distortion and propagation delay are orders of magnitude better, allowing the replacement of optos in every digital application.

There are few new digital isolation applications being designed with the optocoupler today, but many industrial applications such as panel switch protection, elevator control, remote lighting, motor control and power supply control still use optos. For manufacturers selling these control modules there is a great opportunity for cost savings through reduced size in circuit boards and reduced cost per isolated channel.

Passive Input Digital Isolators

Incidentally it’s a common misconception that opto applications which have non-digital inputs such as 110V line voltages can’t be handled directly using a digital isolator. Even that is easily done and offers the same advantages as digital, including fewer components and multi-channel isolators.

Isolator Regulatory Approval

One of the most daunting tasks of any isolator application development is deciding on the regulatory approval approach to take. In the USA it is universally accepted that UL1577 is the regulatory standard of choice for an opto or its digital isolator equivalent, but many products made in the United States for sale in the EU or Asia must also have IEC regulatory approval. These standards consider much more than UL, including the application itself, the environment the finished product will operate in and the non-uniformity (high speed voltage spikes) of the voltage across the insulation barrier. A suite of as many as five standards may be applicable.

RDI has extensive experience driving products through the regulatory process and can advise on every step of the way, including the standards you should apply for. We’ll even take the entire task on board on your behalf if required.

Contact RDI today and discover the benefits digital isolators offer over optocouplers. If you’re designing new hardware or looking to cost reduce an old cash cow, replacing the optos in the system could be the smart move you’re looking for.

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