Power supply design for avionics has become an area of increased
activity over the past few years.
New to the market are industrial-quality, high-current,
lithium-based battery systems. Available from a variety of vendors,
these batteries are characterised by their low weight and high
energy availability.
In avionics and terrestrial mobile applications, every pound saved
counts. Typical older equipment provided portable power with heavy
lead acid battery systems.
Redesigning older lead acid battery systems can reduce weight by
50% or more without sacrificing stored energy performance.
Couple low-mass lithium batteries with reduced-weight electronics
design and a modern battery power supply can vastly improve the
available energy to weight ratio of the entire power system.
Efficiency improvements
Power supply efficiency improvements can be achieved through
careful selection of the power supply topology for the required
application.
Good power supply design can achieve 90% core efficiency. This
high-frequency forward converter design was optimised for a
particular voltage current load curve.
Core efficiency refers to the actual switcher design efficiency
prior to application of additional features. Supervisory features
such as over and under voltage lockout, current fold-back, over
voltage detection, redundant controls, and power factor correction
can rapidly eat away at a power supply’s core efficiency
number.
Power supply reliability and proven mean time between failures
(MTBF) – in short, design quality –
is of paramount importance in avionics.
Power supply reliability can be greatly increased through
conservative design techniques. This requires design
discipline.
A high reliability power supply design is one in which every
component part has been analysed.
A component’s normal operating range, de-rating curves, altitude
effects, and known useful life characteristics must be considered
by the conservative designer. Experience counts when making
component selection. Often a thankless task, part selection is
easily 75% of the challenge in high-reliability design.
Balancing circuit board physical area constraints, de-rating
requirements and component cost is a delicate art. The best
designs are achieved when component selection is not rushed.
Power supply hot swap and load sharing features have become
extremely popular. The ability to swap one power module for another
results in greatly reduced overall system mean time to repair.
(MTTR) When aircraft service or terrestrial vehicle service must be
performed quickly, low MTTR power supply sub-assembly designs
really help.
Use of low-cost edge finger contacts, modular sub-system design,
and the ability for sub-systems to load share makes hot swap
possible.
Diode FET output stages can perform load sharing with great
efficiency, low cost, low weight and low heat. Microcontroller
supervision can add a layer of system-level monitoring of power
supply health.
Power systems based on Intelligent Platform Management Interface
(IPMI) provide an industry-standard method of performing power
management. Alternately, custom communications can be implemented
to supervise power management.
Author is Paul Nickelsberg, president at
Orchid Technologies