LED control card brings new opportunities and challenges for LED lighting

In the past ten years, the automobile electronic products with rapid development of vehicle electronic control, vehicle information and entertainment service system both in quantity and in fine degree are improved greatly.

LED lighting

Such as small size, low power consumption and fast turn on time and other advantages to create a high brightness LED is widely used in today's car situation. The initial application of LED in the car is the central elevated parking lights (CHMSL); the control of LED and LED card application uses red LED to provide a very thin lighting array, the array illuminator is easy to install, and never need to be replaced.

Incandescent bulbs are traditionally the most economical light source and are still used by many cars. However, with the increasingly narrow space available for lighting and the continuous improvement of the service life of the lighting source, the light color and design scheme provided by LED is rapidly replacing the incandescent bulb. Even the traditional CCFL TFT-LCD backlight applications, is gradually being replaced by white LED array.

What's more, people are using a kind of electric "steerable" high current LED array to develop the headlight, which has been controlled by the halogen / xenon filament design. Almost all automotive lighting applications (including interior / exterior lighting and backlighting applications) will gradually transition to the use of LED. The benefits of using LED have many positive implications. First, and perhaps most important, it never needs to be replaced because of its 100000 - hour solid life (service life: 11 and a half years) longer than the life of a car. This allows the car manufacturers to permanently embed them in the cockpit lighting system, without the need for the replacement of the filament bulb as before. Since the LED control card illumination system does not require the installation depth or area required by the incandescent bulb, the shape of the vehicle can be changed significantly. Another advantage of LED lighting and LED control card system is its low power consumption, which can reduce fuel consumption.

Design parameters of automotive LED lighting

In order to ensure optimal performance and long working life, the LED requires an effective drive circuit for both the LED control card. These LED control card driver circuits must be able to obtain a working power supply from a fairly demanding automotive power supply, but also should have both cost and space benefits". In order to maintain its long working life, must not exceed the current and temperature limits of LED.

In a single LED to three (Series) the LED application will require a buck LED control card for bus voltage (nominally 12V) to a more suitable LED voltage, LED color and brightness according to the application requirements of the different range of the LED voltage in 2.68V to 4.88V (each LED). On the contrary, in the application of the LED series such as the brake lights, which require more than 8 series LED, the output voltage is 21V to 39V, so it is necessary to use a boost LED control card.

A constant current source must be obtained from the LED control card IC in order to generate a constant LED brightness at the input voltage. An internal sense resistor is used to monitor the output current to achieve accurate current regulation. The high output current accuracy is maintained over a wide current range (35mA to 1A) to achieve a wide dimming range. In many applications, especially in the back lighting and interior lighting, it may be necessary to adjust the light control, which requires the LED control card provides a simple way to adjust the output current /LED brightness. The use of a suitable LED control card, you can through a PWM signal, DC voltage or external NMOS transistor to complete dimming operation, dimming range of up to 3000:1.

Dual LED applications

Many embedded high current LED applications will include a single or two high current (ILED range from 1A to 1.5A) LED. These applications include in vehicle lighting (e.g., car light, map light, storage box lighting) and off vehicle lighting (for example: door sill light or "ground light"). Depending on the application, they can be used for color LED (back lighting for vehicle instruments) or white LED (for general lighting). Since these LED typically have a forward voltage of 3V to 4V and are powered by a 12V to 14V bus, it is necessary to adopt a buck LED control card.

Dual channel, 36V, 2MHz step-down LED control card, designed for use as a constant current dual LED control card driver. Each channel has an internal sense resistor and dimming control, making it ideal for driving LED that requires up to 1.5A current. The switching operation of one channel is different from that of another channel by 180 degrees, so that the output ripple of the two channels is reduced. Each channel independently in a wide current range of 50mA to 1.5A output current to maintain a high degree of accuracy, and provides a range of unique 3000:1 dimming circuit, and did not produce any color offset (this phenomenon is common in current LED dimming in).

The LED control card adopts the high voltage side detection to realize the grounding connection of the LED negative electrode, thus eliminating the need for a grounding wire in most applications. It also has an integrated boost diode for each channel, thereby further reducing the area and cost of the solution. Additional features include LED open and short