Design Articles

Many systems require that the primary source of DC power be converted to other voltages. Battery driven circuitry is an obvious candidate. The 6V or 12V cell in a laptop computer must be converted to different potentials needed for memory, disc drives, display and operating logic. In theory, AC line powered systems should not need DC-DC converters because the implied power transformer can be equipped with multiple secondaries. In practice, economics, noise requirements, supply bus distribution problems and other constraints often make DC-DC conversion preferable. A common example is logic dominated, 5V powered systems utilizing +15V driven analog components.

The range of applications for DC-DC converters is large, with many variations. Interest in converters is commensurately quite high. Increased use of single supply powered systems, stiffening performance requirements and battery operation have increased converter usage.

Historically, efficiency and size have received heavy emphasis. In fact, these parameters can be significant, but often are of secondary importance. A possible reason behind the continued and overwhelming attention to size and efficiency in converters proves surprising. Simply put, these parameters are (within limits) relatively easy to achieve! Size and efficiency advantages have their place, but other system-oriented problems also need treatment. Low quiescent current, wide ranges of allowable inputs, substantial reductions in wideband output noise and cost effectiveness are important issues.