As electronics continues the quest for miniaturization, the space available
for the power supply will continue to shrink, demanding ever higher output
power density . Maintaining control of this necessary growth to ensure that
reliability is not compromised in the process must be a major concern of
program management. Factors that affect the increase in output power density
are advanced design techniques and components.
Increasing switching frequencies from 20-40 kHz to 100-500 kHz or higher is
presently the most significant technique used to increase power density. This
reduces the size of the magnetics and filter capacitors. Higher power field
effect transistors and newer devices are replacing conventional bipolar
devices. Power hybrid microcircuits and monolithic integrated circuits for
power supply functions are becoming available for military applications.
Capacitor volume continues to be a burden; however, improved versions of both
aluminum electrolytic and tantalum capacitors are becoming available.
Packaging techniques have a direct bearing on increasing output power density.
Examples include rectangular capacitors and both flexible and multi layer
printed wiring boards.
Selection and conservative application of components in power supplies is
critical to ensuring a highly reliable design. Maximum usage of military-
qualified standard components is recommended. However, rapid advances in power
supply design technology and availability of new, higher capability, high-
reliability components have resulted in making some of the standards obsolete.
Military qualification and standardization of new power supplies has not kept
pace with switching-mode power supply design technology. Application of new
technology to power supply design and production can result in meeting the
power density requirements while in fact increasing the reliability.
Examples of qualifiable components for power supply applications include
higher power Schottky diodes, bridge diode assemblies, highly integrated
regulator circuits, analog optical isolators, metalized polypropylene
capacitors, printed wiring board connectors, isolated-case power transistors
and power field effect transistors. Until such are qualified as military
standard, their use requires the exercise of existing government procedures
for nonstandard component approval. The use of nonstandard components in
switching-mode power supplies should not be prohibited, provided there are at
least two independent sources.