标签: low-power

Low-voltage design gets most of the attention these days, but there are many applications which require very-high voltages even though they do not deliver significant amounts of current to the load.   It's easy to think that almost "everyone" is doing low-voltage designs with power-stingy, battery-operated circuits -- but that's a simplistic and myopic perspective. There are well-known exceptions to the low-power world in applications which must deliver significant power to a load, such as a heater or motor. In those situations, using higher voltages allows use of lower currents for a given power rating (P = V × I), while minimizing IR loss and I2R heating. In these cases, current ratings in tens or hundreds of amps are common.   But it’s not all about higher voltages when it comes to reducing current, even though the current may still be in the tens or hundreds of amps . There are many unavoidably high-voltage situations which are also fairly low current, often under 100 mA. This became fairly evident when I walked the exhibit floor at the recent fall meeting of the Materials Research Society , the world's leading scientific organization for researching, developing, and applying new and existing materials. Approximately 6,800 attendees explored nanomaterials, ultrapure materials, cryogenics and ultravacuum chambers, high-temperature furnaces, sputtering, vapor deposition, specialized instrumentation, and much more.   We routinely and somewhat casually rely on many materials-related technologies which enable our hi-tech advances and innovations; it's a synergistic relationship, of course, as these advances in turn drive new materials. Beyond the development of these materials, there are major issues in determining their electrical, physical, and chemical properties. After all, once you have created that amazing ultrapure nanomaterial, how do you measure its hardness?   Why the need for the high voltages and low currents, as seen at many exhibits at the MRS event? These systems and their instrumentation are not "power devices" in the conventional sense, and minimizing IR loss and I 2 R dissipation is not the primary concern. The need is simple: it’s the law of physics. These systems require high voltages to steer electron beams, attract and accelerate particles, and change the energy state of atoms. I saw many specialty vendors whose supply product lines began at 10 kV, as well as many high-voltage supplies embedded within highly specialized analysis, fabrication, and measurement systems. Consumers also have a need for voltages in the 10 kV range, to power the magnetron in their microwave oven, and in past times, for the venerable CRT of now-obsolete television displays.   The standard home microwave oven has a high-voltage supply, usually between 10 and 20 kV, to energize the 2.4 GHz magnetron inside; would knowing that detail scare the consumer? SOURCE: Wikipedia   For designers who have little or no exposure to high-voltage/low-current design, it's a very different world. There's little need to minimize IR loss by using heftier connectors and conductors, since voltage drop is not a primary concern at these low currents. Instead, it's a world of thin conductors, thick insulation, safety interlocks, and mandated minimum physical spacing between conductors and anything nearby. It's also an unforgiving world where marginal design, inadequate attention to tiny details, and microscopic cracks in insulation can have dangerous consequences for equipment and users.   Nothing is done quickly, easily, or casually: voltage/current monitoring, probing with test equipment during debug or repair, and designing for user access must all take into account high voltages and its tendency to go through any breach in system physical integrity. Seeing a 25-kV rail cause spark-over in an poorly placed capacitor is an experience you won't forget (who, me?). Every component must have appropriate ratings and certifications, and even something as normally mundane as insulation material, thickness, and breakdown rating is a concern. Further, any tiny nicks in the insulation which may occur during prototyping and debug stages, or in production manufacturing are also a concern. Routine electrical insulation and standard electronic signal-isolation techniques and components are neither routine nor standard.   Designers who work in low-voltage, low-current domain have the luxury of being able to route power as they want to and make changes as needed to satisfy PC board-layout and cable-harness priorities; you can rout a 3.3V rail (on the PC board or in a cable) pretty much wherever you wish. In high-voltage designs however, that degree of freedom doesn’t exist and any change in routing must be carefully assessed to make sure it doesn't violate appropriate design guidelines or numerous regulatory standards for placement, creepage, clearance, and safety. Low-voltage designers don't have to worry that the basic design or any change in it will trigger safety-related regulatory testing and approval cycles.   Have you ever been directly involved with high-voltage/low-current design? Have you ever worked on a project which had that aspect? If so, what intrigued, impressed, worried, or scared you the most?