Power Hotspot

Current transformers measure current or transfer energy from one circuit to another, so their design requires calculations different from their voltage transformer cousins. The reason for the difference is that current transformer magnetizing current is the load current itself, unlike voltage transformers, where magnetizing current is "separated" from the load current and has a value that's a small fraction of the total current at full load. We want to supply the load with...

One highlight of the January auto shows was General Motors' Chevy Volt, a hybrid concept vehicle targeting a 40-mile all-electric range using lithium-ion batteries and a small generator driven by a gasoline engine. It was interesting to note that ultracapacitors did not figure in the design. (The Tesla Motors Roadster doesn't use ultracaps either.) Ever since many-Farad ultracaps became available several years ago, they've been touted as a complement to batteries...

Designers making in-circuit current measurements can avoid ground-reference problems by putting the sense resistor on the supply side of the load. However, high-side measurement components must deal with high common-mode voltages. To make high-side differential measurements across a sense resistor, the HV7801 and HV7802 high-side current monitors from Supertex offer an 8- to 450-V input voltage range. They also provide 700-ns rise and fall times. In the HV7802, IOUT...

Here's a synchronous, current-mode, step-down dc-dc controller with differential output voltage sensing. Using a pair of VSENSE inputs like this enables high-accuracy regulation in high-current applications. Linear Technology's LTC3823 can either sense the voltage drop across the synchronous power MOSFET, or where control of maximum output current is important, it can be used with a sense resistor in series with the source of the lower MOSFET. It has a 4.5- to 30-V...

Hello Mr. Pease: I've read somewhere that it can be a problem for the op amp to lose one of the supplies or use the wrong startup sequence. (You are correct. A startup sequence can cause great trouble on the positive and negative rails. /rap) Is it always a particular rail? Can you shed some light on the cause of this? Does it apply for bipolar and CMOS families? • David Smith • Pease:...

Imagine filling up your gas tank once— and then ignoring it for the next 640 miles. Or if you drive less than 40 miles a day, imagine never filling it up again. That's the promise of the Chevy Volt, GM's latest concept car, unveiled at last month's North American International Auto Show in Detroit (...

Measuring current is always a nuisance because you have to break the circuit to put the measuring device in series with the circuit. That problem never goes away. Still, any high-end digital multimeter can accurately measure currents down into the microampere and high-nanoampere range. But the process gets tricky as the current levels fall into the low-nanoampere and picoampere ranges. At these levels, noise becomes a real problem. Also, the internal impedances of the measuring...

The AMC.0 R.2 specification from PICMG (PCI Industrial Computer Manufacturers Group) increases the maximum power for MicroTCA cards by 60 to 80 W and the management power from 100 to 150 mA. It also defines a new midsize module and better LED faceplace placement guidelines. Additions were made as well allowing press fit, surface-mount, and through-hole style connections versus the initial compression-fit style along with support for a variety of ejector handles that will increase the areas...

A precise, temperature-compensated voltage reference circuit lies at the heart of every analog-to-digital converter. Voltage-reference technology hadn't changed fundamentally in decades until last year, when Intersil announced a single reference chip based on precharging a floating gate. The company now has announced several additional voltage references. But first, let's look at the technologies. "Bandgap" voltage references have been around since Bob Widlar developed...

There's a new opportunity to design added-value power supplies and chips that help data centers conserve electrical power. The problems that IT managers face today are nothing less than monumental. Consider a historical analogy. Aluminum Smelters And Data Centers Bonneville Dam, present capacity 1.05 GW, began generating energy in May 1938 (...

What is a synchronous rectifier? A synchronous rectifier is a circuit that emulates a diode, allowing current to pass in one direction but not the other without the losses associated with junction or Schottky devices. The circuit comprises a pass-element (most often a power MOSFET), a sense element, a sense-signal conditioner, and a driver. How does a synchronous rectifier work? There are two broad techniques to implement the...

In reaction to the U.S. Environmental Protection Agency's (EPA) recently announced Energy Star 4.0 guidelines, power efficiency has become the dominant issue within powermanagement design. Hewlett-Packard will offer 80% efficient power supplies as an option for the recently introduced HP Compaq dc7700, dc5700, and dc5750 series desktop business PCs this month. Not only that, the optional supplies let HP meet the Energy Star guidelines six months before they take effect. The most...

For many handhelds, lithium-ion (Li-ion) batteries have become the power source of choice. In response, IC manufacturers are developing devices that operate properly using the normal output voltage of these batteries. In other words, the nominal Li-ion output of 4.2 V will drop down as low as about 3 V as it's used. An IC then should be able to work with an input voltage of at least 3 to 5 V so it can accommodate a single Li-ion cell. National Semiconductor's LM3671 step-down...

Watch an LCD TV or surf the Web on your refrigerator. Chat with your washing machine. Let your dishwasher decide when the dishes are done. Enjoy a hot cup of joe with just the right amount of cream and sugar, dispensed by your coffee maker with skill that would put any barista to shame. And you won't need to wait decades for these advances. They're happening right now. There's a revolution in modern white goods as the industry moves from its electromechanical ...

With all the sausages, pastries, and beer I consumed, I should have put on a few pounds at Electronica. But I walked several miles each day at the show, trying my best to cover 3500 exhibitors spread out over 14 halls, racing from meeting to meeting. Despite the calories burned, there was no chance of seeing it all. Yet I still saw loads of new technology, much of it related to power management and energy efficiency in white goods, as well as Ultra-Wideband (UWB)...

Applications that often require MOSFETs with 200-V breakdown ratings include high-powered (up to 1000-W) class D audio amps, 48-V output ac-dc supplies (for synchronous rectification), brushless dc-motor drives (up to 1 hp), and isolated dc-dc converters operating from a universal input range (36 to 75 V). To deal with those applications, International Rectifier s first DirectFET-packaged MOSFET offers a 200-V breakdown voltage rating. Previous DirectFET MOSFETs offered a maximum breakdown...

The factory floor is changing radically. Usually powered by batteries, wireless sensors have been available for transmitting data for quite some time. The greater use of wireless communications standards like ZigBee has accelerated these applications. But sensor batteries have limited lifetimes and require frequent replacement, limiting their use. The PMG7 microgenerator module from Perpetuum Ltd. lifts these restrictions. This small, 190-gm module converts the kinetic energy of...

If you found one of these PCs on your desk, your eyes would light up. The quest for more computing power never ends, but 2006 saw some significant steps forward. QUAD CORE MOTHERBOARD Intel's Core Duo 2 Extreme QX6700 processor packs four cores into a 775-landing multichip package (...

Welcome to our second annual Best Electronic Design issue, in which we select and honor some of the most innovative designs of the year. The pace of innovation continued at an astonishing rate in 2006, and this issue highlights some of the technologies you readers have chosen as significant to advancing electronic design. It also gives us the opportunity to honor some of the outstanding end-product designs you have produced in the last year. This issue puts 2006's top innovations...

Rising fuel prices and the nation's dependency on foreign oil— as well as increasing air pollution—are spurring a quest for alternative power sources. Tesla Motors is offering one solution with its Roadster electric car. Powered by rechargeable lithium-ion ( Li-ion) batteries, this sports car has a range up to 250 miles on one battery charge, depending on driving conditions (...