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The exploration of power-control devices and techniques

The exploration of power-control devices and techniques deals with the tried and proven as well as with the new. It is not always easy to identify the difference between ordinary power devices and those that might do justice to such labels as sophisticated, exotic, or smart. Most bipolar power transistors of the types that have faithfully performed in myriads of power circuits, such as regulators, amplifi­ers, and motor control, are ordinary traditional devices. Admittedly, some bipolar power transistors with inordinate switching speed, frequency capability, or current or voltage ratings are certainly not garden-variety devices. Perhaps a reasonable test is to judge in terms of performance generally achieved five or ten years ago. If there has been a definite advance in certain parameters of performance, the device might well qualify as an extraordinary one; (that is, one that is of special interest for modern designs) and as a possible forerunner of future development.

Interest in the newer and smarter power devices does not necessarily imply that the device must be integrated or associated with a microprocessor. Generally, there will be one or more plus features over devices commonly used a few years ago. For example, the modern power Darlington produces power gains not readily realized in the elemental power transistor. And, power MOSFETs require so little drive that they certainly merit classification as a modern power device destined for greatly expanded application in future designs of control circuits and systems. Then, too, power op amps and power Ics can do things beyond the capabilities of ordinary power transistors, unless assisted by auxiliary devices and circuitry. Even more suggestive of future trends are the now-developing families of dedicated devices and those with self-contained logic or drive circuitry.

The ultimate development of such smart power devices is a complete system or subsystem within a module. The basic idea-instead of a collection of discrete devices, stages, and associated passive components. All or most of the power-control function is accomplished within a single package. Not shown is internal protection against overload, transients, and temperature rise. This concept is ideal. There are thermal, electrical, fabrication, and cost factors that mitigate against universal realization of such an elegant format. (2382)

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