Volume 89 (July 15, 2009)

Dr. Eco's Mini-Seminars (1): Eco-Friendly Lights (LED)

We have begun a mini-seminars to introduce NEC Electronics' semiconductors, which have gained attention for their contributions to the environment. Hello! my name is Dr. Eco. I will be your guide. In this mini-seminars, we will welcome a lecturer for each topic, and discuss semiconductor technologies that contribute to the welfare of the environment. At the same time we will also look at market trends and fields of application. Our first lesson focuses on driver ICs and microcontrollers that power LEDs.

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Our lecturer for this mini-seminars
Kouzou Nakata
Senior System Integrator, Power Management Devices Division.

Why does using LEDs save energy?
Let's look into the answers together with Dr. Eco, from the workings of LEDs to produce light, to the semiconductors that drive LEDs.

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LEDs are energy-efficient, bright, and long-lasting.

What is LED?

LED stands for "Light Emitting Diode." It is a type of semiconductor that produces luminescence when an electrical current flows. LEDs of various colors have been developed, such as red, green, yellow, blue, and white. They have been noted as an energy-saving light source different from conventional electric bulbs and fluorescent tubes.

How much energy do LEDs save?

Compared to electric and fluorescent tube, LED's energy-saving benefits are low energy consumption, high luminescence, and long lifespan. For example, when it comes to lighting, to achieve the same luminance as four electric bulbs, 18 (*1) 2W LEDs are needed. However, LEDs consume about just 19% energy compared to electric bulbs. In other words, LED can bring about brilliant illumination with low energy. The diode itself emits light, and unlike a light bulb, it does not stop functioning because of broken filaments. The lifespan of LEDs is 10 to 100 times greater than that of electric bulbs.

What kinds of things use LEDs?

Recently, outdoor electronic signs, illumination displays, streetlights, traffic signals and interior illumination have begun to use LEDs. It is highly likely that LEDs will replace electric bulbs in traffic signals, which can be difficult to see when the sun is strong in the west, so they can be seen clearly.

4-Channel Control Capable LED Drivers

What do we need to consider when using LEDs?

LEDs are, without exception, low in energy consumption, high in intensity, and long in lifespan. However, they have a disadvantage when it comes to high temperature. If the ambient temperature rises, the resistance of the LED drops, and a large amount of electricity flows through. As the current increases, the temperature of the LED itself also rises, and resistance further weakens. Repeating this cycle over and over brings the risk of damage to the LED. Even if the LED does not break, the voltage and electrical current become variable depending on the color, and the brightness changes depending on the temperature. To prevent such variability, a (constant current driver) circuit (IC) for flowing constant current to LEDs is necessary.

What are needed for ICs to provide constant current?

Like power supplies in general, there are two types of systems: series regulator and switching regular. LED lighting needs a large amount of current, so the highly-efficient switching regulator is a more suitable choice. NEC Electronics' µPD168804 is an LED control IC that incorporates this switching system.

Tell us about the features of LED driver IC µPD168804.

With constant-current driver IC setting packaged into one 4-channel chip that can drive up to a maximum of 1500mA using external power MOSFET and resistance, the µPD168804 is the perfect product for creating high-power LED illuminations and performance lighting. The four channels can each be controlled independently. For example, until now when LEDs combining four colors, such as RGGB (red, green, green, blue) or RGBW (red, green, blue, white), are used for performance lighting, one control IC was required for each LED. With the µPD168804, the control circuits for four channels are packaged in one chip. With one component as all that is needed, it is possible to reduce the number of components in a set, space, and cost, and make the system more environmentally friendly.

The input voltage similarly supports a wide range from 9 to 38V. Internal voltage can be stepped up or down based on setup of external component and mode selection. For example, when the input voltage is 12V, it is stepped up to 32V in order to use eight LEDs, and stepped down to 5V when one LED is used. Because the IC can be used differently depending on the number of LEDs, components such as substrates can be shared to the greatest extent possible.

What is needed to carry out complex control of LEDs, such as for illumination displays?

By combining LED drivers with microcontrollers, which control the overall set, one can create flashing illumination with LEDs and control the speed of blinking. Displays, pictures, or text that use a large of LEDs for requiring complex operations can also be created.

To further reduce the number of set components, space, and cost, we developed the 8-bit All Flash microcontroller µPD78F8024/25 to meet the needs of customers who wanted onboard LED driver function in a microcontroller. In addition to the functions of the LED driver IC µPD168804, features such as I²C and UART communication interfaces and A/D converter are embedded with the microcontroller function. Thus it is possible to have more precise controls of communication-based control and sensor inputs for detecting temperature and brightness. Depending on the needs of the customer (specifications, size, etc.), for a single color, a single-package LED driver IC or driver-embedded microcontroller can be used. To control multiple colors, LED driver IC and general-purpose microcontroller can be combined. For 8-channel control, LED driver IC and driver-embedded microcontroller can be used at the same time.

So, to create a stable pattern with LEDs, drivers and microcontrollers are essential. And, not only LEDs but drivers and microcontrollers contribute to the welfare of the environment. Thank you, Mr. Nakata!

Further Applications of LEDs

The range of LED applications is expected to broaden, from automobile headlights to LCD TVs to home lighting. Because LED is small, the freedom of design is expanded. It promises to bring about unique lighting hardware. At work behind the environmentally-friendly future lighting (LEDs) are NEC Electronics' LED driver ICs and All Flash microcontrollers. They are working to bring about an eco-friendly society.

Note (*)

Dr. Eco's Tidbit of Knowledge — LED Streetlights —

Recently, streetlights using LEDs can be seen. Compared to conventional fluorescent tubes, they consume half the energy. Furthermore, LED street lamps powered by home solar panels have made their debut, so streets can be lit in the night with just a little bit of power. To not extinguish is the major requirement of a street lamp. By using multiple LEDs, even if one LED is damaged, the remaining LEDs can compensate. By using the LED driver IC µPD168804, four LEDs for the same white color can be used per device to implement a street lamp that does not extinguish. Also, the 8-bit All Flash microcontroller µPD78F8024/25 can be used to control a lamp so that its brightness does not diminish even if an LED is broken. By receiving information such as change in current and input from the brightness sensor, the microcontroller can send commands to increase the amount of current per LED and maintain the same level of brightness. This shows how indispensible LED driver ICs and microcontrollers are to LED streetlights.

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