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Current Drivers Help Avoid Bright Spots in High-efficiency Electronic Signs

Tue, 11/24/2009 - 9:22am
STMicroelectronics, a leading developer of semiconductors for LED lighting, has announced a new series of highly accurate LED drivers with automatic power saving, enabling electronic signage such as road signs, advertising, stadium displays, battery or solar-powered signs and similar equipment to deliver better, high-resolution viewing by ensuring consistent brightness across the viewing area.

The brightness of an LED is closely related to the drive current, usually supplied by a separate driver chip. As each new generation of LEDs produces greater brightness at lower drive current, overall efficiency is increasing but so, too, is the need for more accurate current control. This control is essential to prevent excessively bright or dark areas from damaging the visual effectiveness of signs and screens, which can employ tens of thousands of individual LEDs.

To provide the enhanced current control designers need, ST has introduced a family of driver chips capable of supplying 16 LED channels with driving capabilities of 3mA to 40mA and bit-to-bit accuracy within ±1%. This accuracy is superior in tolerance to alternative drivers providing comparable drive current. In addition, as a large display may require several thousand drivers, ST’s new devices also provides excellent current matching from chip to chip (±2%) to further enhance visual performance.

The new LED drivers are the STP16CPP05, STP16CPPS05, STP16DPP05 and STP16DPPS05. In addition to their enhanced current accuracy, they also provide optional features including ST-patented automatic power saving, as well as built-in LED error detection. Available variants allow designers to specify either or both of these value-added features, in a choice of four industry-standard package options.

The patented automatic power saving allows the drivers to turn off independently when no LED drive data is provided. This function delivers two benefits: software design is simplified as no power-save algorithm is required; and power savings are increased as the drivers turn off more quickly than is generally possible under software control.

Error detection helps to improve maintenance and boost productivity for signage operators. If an LED in the display fails, ST’s LED drivers can detect either of the two possible failure modes (short circuit or open circuit) and communicate the failure to a central point. With this information, the system could be programmed to inform field maintenance crews of the necessary replacement parts in advance. In applications such as road signage, where reliability is critical, this feature can enable faults to be repaired quickly and efficiently.

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