Download ISOLATION VOLTAGE

ISOLATION VOLTAGE
Application Notes
WHAT DO THE FOLLOWING TERMS REALLY MEAN?
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Hi Pot Test
Withstand Voltage
Dielectric Withstand Voltage
Flash Tested
Proof Voltage
A question commonly asked is:
■ What is the continuous voltage
than can be applied to the part in
normal operation?
These are all terms that apply to various
aspects of the same thing:
■ A test voltage, applied for a
specified time, across a component
designed to provide electrical
isolation, to verify the integrity of
that isolation.
C&D Technologies isolated dc/dc converters,
power supplies, and pulse transformers are
all 100% production tested for their
respective isolation characteristics.
This is usually done by applying a high
voltage between the input and output
connections although on some power
supplies and converters, a high voltage is
also applied between the I/O connections
and the metal baseplate or chassis. The
actual voltage and time duration of the test
varies by model but is always specifically
defined on the product data sheets or is
inferred by the specific safety agency
approvals. While the duration of typical
production hi-pot tests is typically 2-5
seconds, safety agency testing for
certification is conducted for 60 seconds
during the Design Verification Testing to
ensure an adequate design.
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As isolation testing isn’t considered to be
“continuous”, the answer to this question isn’t
very clear. The isolation test represents a
validation of the dielectric strength of the
isolation barrier against transient voltage
events. The part, therefore, should never be
used as an element of a safety isolation
system under such continuous exposure.
PARTS WITH NO AGENCY APPROVALS
For a part holding no specific agency
approvals, however, both input and output
should normally be maintained within SELV
limits, i.e. less than 42.4VAC peak, or 60VDC.
In specific applications, the part could be
expected to function correctly with several
hundred volts offset applied continuously
across the isolation barrier. Under these
conditions, however, circuitry on both sides
of the barrier must be regarded as operating
at an unsafe voltage and further
isolation/insulation systems must form a
barrier between these circuits and any user
accessible circuitry to comply with safety
standard requirements.
SAFETY AGENCY APPROVED PARTS
With safety agency approved parts, the
situation is quite different. Here the parts
have a continuous working voltage rating
dependent on approval level - which, in turn,
depends on the internal grade of insulation.
Standards such as UL60950 give tabular
details of working voltages and their
associated test voltages.
C&D Technologies (NCL) Ltd
Tanners Drive, Blakelands North
Milton Keynes MK14 5BU, England
Tel: +44 (0)1908 615232
Fax: +44 (0)1908 617545
email: [email protected]
C&D Technologies (NCL) Limited reserve the right to alter or improve the
specification, internal design or manufacturing process at any time,
without notice. Please check with your supplier or visit our web site to
ensure that you have the current and complete specification for your
product before use.
C&D Technologies Inc.
3400 E Britannia Drive, Tucson,
Arizona 85706, USA
Tel: +1 (800) 547-2537
Fax: +1 (520) 741-4598
email: [email protected]
No part of this publication may be copied, transmitted or stored in a
retrieval system or reproduced in any way including, but not limited to,
photography, photocopy, magnetic or other recording means, without
prior written permission from C&D Technologies (NCL) Limited.
© C&D Technologies (NCL) Limited 2004
GEAN-04.1
Instructions for use are available from: www.cdpoweronline.com