MS-2341 Datasheet, PDF (1/5 Pages) Analog Devices – Surging Across the Barrier

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Surging Across the Barrier:
Digital Isolators Set the
Standard for Reinforced
Insulation
INTRODUCTION
Optocouplers have traditionally been used to isolate
potentially dangerous voltages in many types of electrical
equipment. Today, more modern digital isolators based on
transformer or capacitive coupling are widely used.
Transformer-based digital isolators offer many benefits such
as improved performance, integrated functionality, lower
power dissipation, better longer-term reliability, and
improved ease of use.
Isolation can be required for several reasons. It allows
functional circuit operation when disparate ground
references or supply voltages are used. Equipment operators
or medical patients must be protected from shocks or
dangerous currents during long-term system operation.
Damage to sensitive and/or costly systems due to electrical
surges—such as lightning strikes—must be prevented.
Over time, national and international standards were
developed with the goal of providing uniform specification
and testing of isolators and electrical systems employing
isolation. Safety certifications can be achieved both at the
component level and for the end system, and certification
requirements can vary in different regions of the world even
when the same base safety standards are referenced. Isolators
that meet a superset of safety standard specifications provide
maximum flexibility to equipment vendors in meeting these
varying requirements.
Technical Article
MS-2341
There are a variety of reasons for requiring galvanic isolation
in electrical systems. The most obvious—and most critical—
is the protection of human operators from potentially lethal
shocks. Shock hazards can come from the mains power that
the equipment is plugged into, or from high voltages
generated within an enclosure. A reinforced insulation rating
is required when humans are being protected from
potentially lethal shock.
In large industrial settings there may be potential differences
between physically separated ground points that may create
unwanted current flow. Ground loops can also lead to noise
and hum in a system.
High reliability or high availability systems often require that
individual circuit faults be contained such that overall
system operation is not impaired beyond an acceptable level.
Isolation can be used in these systems to contain faults so
neighboring circuitry remains operational.
Different portions of an electrical system may have
unreferenced grounds or be referenced to unrelated high-
side supply voltages, again leading to a need for isolation.
Finally, noise in a particular portion of a circuit may need to
be contained to eliminate interference with sensitive
electronics.
SAFETY STANDARDS
The International Electrotechnical Commission (IEC)
publishes a number of international standards related to
electrical safety, while national bodies such as Underwriters
Laboratory (UL) in the US and Verband der Elektrotechnik
(VDE) in Germany publish regional specifications. Testing
and certification to the standards is provided by several
entities, including UL, VDE, the Canadian Standards
Association (CSA), and Technischer Überwachungs-Verein
(TÜV) in Germany. The choice of which certification to
obtain depends on the region where the component or
Table 1. System-Level Standards Relevant to Applications Requiring Isolation by Market and Region
Household Industrial
Information
Technology
Measurement and
Control
Medical
International IEC 60065 IEC 60204
IEC 60950
IEC 61010-1
IEC 60601
Germany
VDE 860
EN 60950
VDE 410/0411
VDE 0750
USA
UL 60065 UL 508, UL 60947 UL 60950
UL 61010
UL 60601
Canada
CSA. 14-10
CSA 60950
CSA 61010
CSA 601
Telecom
IEC 60950
VDE 0804
UL 60950
CSA 60950
June 2012 | Page 1 of 5
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