Machine Design


Power-circuit modules containing several power semiconductor switching devices can reshape ac power into other required forms and often have current ratings from 30 to 50 A. The semiconductor elements in these devices are usually SCRs or triacs and are glass passivated and mounted on a copper-clad ceramic substrate to efficiently conduct heat to the ambient. Common configurations include single-phase half-wave bridges that often contain a freewheeling diode for inductive loads, switches for single and three-phase ac switching applications, and SCR doubles for single and three-phase bridges.

Power ICs: Despite a slow start, smart power is gaining momentum in automotive, industrial, and data-processing applications. In these environments, power ICs typically drive motors, solenoids, and lamps. They also provide power supply and interface functions.

Smart power ICs are the interface between digital control logic and high-power loads. More specifically, the Joint Electronic Device Engineering Council (Jedec) defines them as monolithic or hybrid semiconductor devices that provide signal conditioning and power control, along with fault management and diagnostics. They have a peak output rating of at least 1 A and a voltage rating of at least 30 V for both supply and load.

Power ICs range from simple to complex. Simpler ones may include only a few level-shifting and drive circuits to translate microprocessor signals into voltage and current sufficient to energize a load. Display drivers, for example, fall into this category. Though displays are capacitive in nature, and often solid state, they still require drive voltages beyond what logic circuits can provide.

At the other extreme, power ICs may include load monitoring, diagnostic functions, self-protection, and information feedback to the microprocessor. A typical application for a full-featured power IC is in automotive multiplexing, where distributed smart-power modules can control lights, windows, seats, and air conditioning, reporting to microcontrollers over a two-wire bus.

More than a set of specifications, "smart power" is a new approach to managing electromechanical and other high-voltage loads, using multifunctional components. The three primary functions of smart power are power control, sensing/protection, and logic interfacing.

TAGS: Technologies
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