Their job is to convert high-voltage alternating current from the mains into low-voltage direct current for mobile phones, laptops, iPods and other electronic gadgets.

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Siemens is also offering high-voltage direct current technology, but ABB is a step ahead.

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Its high-voltage direct current system is delivering electricity to the British Petroleum platform in the middle of the ocean.

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One of ABB's specialties is high-voltage direct current links, so-called HVDC.

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Infineon also provides the thyristor chips that allow transformers to handle high-voltage direct-current power lines.

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It's high-voltage, high-current DC, which is not too far off of automotive electronics from a technology standpoint.

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That is the reason why the current emphasis in China is on the construction of 500kv extra-high-voltage lines and long-distance power transmission.

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Large-scale electricity transmission usually uses alternating current, in which both current and voltage oscillate.

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Power electronics modify the voltage, current or frequency of electricity in applications as diverse as solid-state lighting, intelligent motors and electric vehicles.

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High-voltage DC can carry power over long distances at lower cost than alternating current, but the transformers still cost too much to make the idea widespread.

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