Features - Bodo's Power

POWER SUPPLY
Power Conversion Standard
Sets Direction for Suppliers
and OEMs
By Tom Newton, IPC Director of PCB Programs, Standards and Technology
Power conversion devices (PCDs) are used
throughout the computer and telecommunications
industries; however, until now, there
was no defined standard for these devices.
A standard was needed to improve field performance
of power conversion devices,
reduce the overall qualification interval for
these devices and provide customer requirements
for consumer and telecommunications
grade PCDs. As a result, IPC — Association
Connecting Electronics Industries® published
the first-ever power conversion standard,
IPC-9592, Requirements for Power
Conversion Devices for the Computer and
Telecommunications Industries, in September
2008.
The standard was developed by the Power
Conversion Devices Standard Subcommittee
(9-82) of the IPC OEM Management Council
Steering Committee (9-80). It comprises representatives
from leading original equipment
manufacturers (OEMs) and power conversion
equipment suppliers, such as Alcatel-
Lucent, Cisco Systems, Dell Inc., Emerson
Network Power, Hewlett-Packard Co., IBM,
Lineage Power, and Murata Power Solutions.
IPC-9592 details what is required as far as
the mechanical, electrical, environmental,
quality- and reliability-assurance, and regulatory
aspects of power conversion are concerned.
For mechanical, that includes form and size,
connector and wiring configurations, and
cooling needs. The electrical standards
focus on interface specifics, including power
source, input voltage, frequency and current
needs, output voltage and, when applicable,
logic controls. The environmental standards
identify operating and shipping temperatures,
humidity, shock and vibration limits.
The quality/reliability standards include definitions
and requirements for the design and
testing of power conversion devices, and the
regulatory portions of the document spell out
international standards for safety, electronic
interference and environmental impact of
power-conversion devices.
The standard refers to three categories of
power conversion devices (PCDs):
Category 1: dc output power supplies to be
embedded in equipment, whether the input
power is acac or dc.
Category 2: Board mounted dc-to-dc converters
including both isolated and non-isolated
converters
Category 3: ac-to-dc power supplies used
as adapters and chargers that are external
to the equipment being powered.
Product specifications and documentation
requirements should follow a specific set of
guidelines and appear in a delineated format.
Such documentation includes the theory
of operation; applicable schematics; qualification
test plan; reports for electromagnetic
compatibility (EMC), sample qualification
tests, design verification testing (DVT), highly
accelerated life testing (HALT), SMT
power module solder attachment reliability,
and derating; reliability data and calculation;
design checklist; failure mode and effect
analysis (FMEA) for custom products; bill of
materials (BOM); approved supplier list for
all components; PCB artwork; component
drawings, including magnetic; manufacturing
drawings; regulatory reports (if applicable);
change history; and mechanical dimension
measurements.
The data sheet should provide complete
specifications of form, fit and function,
including electrical specifications and
whether it is a Class 1, general or standard
PCD, or Class 2, enhanced or dedicated
service PCD. The date and revision level
should be marked at the bottom of the
sheets. Items to be addressed are input
power logic, indicator, control, and output
specifications; reliability, safety, and regulatory
factors; physical dimensions and electrical
specifications and requirements; and
material control and labeling. In addition, the
PCD supplier needs to implement a documented,
capable material control system for
all incoming, in-process, and outgoing materials
and make available documentation of a
material control plan.
Design for reliability means that industry best
practices to specify, design, and document
PCD performance and reliability are in place.
Expected reliability of a PCD and the conditions
under which the reliability is specified
should be defined by the supplier and the
user’s operating specifications provided. A
documented process must be in place to
select all components for product designs
including information on all components and
all component suppliers. IPC-9592 defines
the factors that should be incorporated into
the component selection process.
An important part of IPC-9592 involves derating
documentation requirements and setting
derating guidelines. To provide a reliable
power conversion product, the standard document
sets forth a method of component
derating to use in all electrical designs. It
provides details on the derating methods,
conditions and results. Derating is a technique
used to ensure that component ratings
are not exceeded, either under steady state
or transient conditions. The intent of component
derating is to improve reliability of electrical
components in electronic products by
compensating for many variables inherent in
a design. Proper component derating will
lower failure rates through reduced stresses;
reduce the impact of material, manufacturing,
and operational variability; and enable
continued circuit operation with long-term
part parameter shifts.
When there is a custom PCD design on new
topologies or architectures with no previous
design failure modes and effects analysis
(DFMEA), or in cases where there are new
technology components, the supplier should
provide a DFMEA to the customer with
results of the analysis and of any corrective
actions. DFMEA is to be performed early in
the power supply development cycle.
DFMEA activities are designed with three
aims: to recognize and evaluate the potential
failure modes of each component in a product
and its effects on the product, to identify
actions that could eliminate or reduce the
chance of the potential failure occurring and
40 Bodo´s Power Systems ® August 2009 www.bodospower.com