LED control card brings new opportunities and challenges to automotive LED lighting
In the past ten years, automotive electronic products have developed by leaps and bounds, and in-vehicle electronic control, in-vehicle information services, and entertainment systems have improved significantly in terms of quantity and precision.
LED lighting
Advantages such as small form factor, low power consumption, and fast turn-on time have created a situation where high-brightness LEDs are widely used in today's automobiles. The initial application of LEDs in automobiles is central overhead parking lights (CHMSL); these LEDs and LED control card applications use red LEDs to provide a very thin lighting array that is easy to install and never needs to be replaced.
Traditionally, incandescent bulbs are the most economical light source, and they are still used by many cars. However, with the shrinking of the available lighting space and the continuous improvement of the service life requirements of the lighting source, the color and design of the light provided by the LED are rapidly replacing the application of incandescent bulbs. Even the traditional CCFL TFT-LCD backlight application is gradually being replaced by white LED arrays.
What's more, people are still using an electric 'manipulable' type high-current LED array to develop headlights, and this field has been controlled by halogen / xenon filament design. Almost all automotive lighting applications (including vehicle interior / exterior lighting and backlighting applications) will gradually transition to adopt LEDs. The benefits of using LEDs have many positive implications. First (perhaps the most important point), it never needs to be replaced because its solid-state life of 100,000 hours (service life: 11 and a half years) is longer than the life of the car. This allows automakers to permanently embed them in the lighting system in the cabin without having to leave an entrance for replacing the filament bulb as in the past. Because the LED control card lighting system does not require the installation depth or area required by the incandescent bulb, it can also make a significant change in the shape of the car. Another advantage of the LED lighting and LED control card system is that it has low power consumption, which can reduce fuel consumption.
Design parameters of automotive LED lighting
In order to ensure the best performance and long working life, the LED needs an effective driving circuit that is both the LED control card. These LED control card drive circuits must be able to obtain operating power from a rather demanding automotive power bus, and should also have both cost and space 'benefit'. In order to maintain its long working life, the current and temperature limits of the LED must not be exceeded.
In the application of a single LED to three (series) LEDs, a step-down LED control card will be needed to reduce the bus voltage of the vehicle (nominal value is 12V) to a more suitable LED voltage, depending on the application of the LED The color and brightness requirements are different. The LED voltage can range from 2.68V to 4.88V (per LED). In contrast, in applications such as brake lights that require multiple LED strings consisting of up to 8 LEDs in series, the required output voltage is 21V to 39V, so a boost LED control card must be used.
If you want to produce a constant LED brightness under an irregular input voltage, you must obtain a constant current source from these LED control card ICs. An internal sense resistor is used to monitor the output current to achieve accurate current regulation. High output current accuracy is maintained over a wide current range (35mA to 1A), thus achieving a wide dimming range. In many applications (especially back lighting and interior lighting), dimming control may be required, so the LED control card is required to provide a simple method for adjusting the output current / LED brightness. Using a suitable LED control card, the dimming operation can be completed by a PWM signal, DC voltage or external NMOS transistor, and the dimming range can be as high as 3000: 1.
Dual LED applications
Many embedded high current LED applications will include single or two high current (ILED range from 1A to 1.5A) LED. These applications include interior lighting (for example: roof lights, map lights, storage box lights) and exterior lighting (for example: door sill lights or 'ground lighting' lights). Depending on the application, they can use color LEDs (for back lighting of in-vehicle instruments) or white LEDs (for general lighting). Since these LEDs usually have a forward voltage of 3V to 4V and are powered by a 12V to 14V automotive bus, a step-down LED control card is required.
The dual-channel, 36V, 2MHz step-down LED control card is designed for use as a constant current dual LED control card driver. Each channel has an internal detection resistor and dimming control function, making it ideal for driving LEDs that require up to 1.5A current. The switching operation of one channel is 180 ° out of phase with the other channel, thus reducing the output ripple of both channels. Each channel independently maintains a high output current accuracy in a wide current range of 50mA to 1.5A, and the unique circuit provides a 3000: 1 dimming range without any color shift. (This phenomenon is very common in LED current dimming).
The LED control card uses high-voltage side detection to realize the ground connection of the LED negative electrode, thereby eliminating the need for a ground wire in most applications. It also has an integrated boost diode for each channel, thus further reducing the solution footprint and cost. Additional features include LED open circuit and short circuit protection.
brake light
To date, the most common application of LEDs in automobiles is central elevated parking lights (CHMSL). By the end of 2006, at least 60% of cars had LED-type CHMSL installed. The benefits include faster lighting speed, higher efficiency, longer working life, and the very thin red LED array also has the ease of design / installation. LEDs can reach full illuminance in less than 1ms (whereas traditional light bulbs require up to 200ms to produce their maximum brightness), this way, the time for the driver of the rear vehicle to recognize the brake lights will be greatly reduced The probability of rear-end collision accident occurred.
Moreover, compared with incandescent light bulbs, power consumption has dropped by as much as 80%, which ultimately has the effect of saving fuel consumption. Its effective life span will easily exceed the life of the vehicle, thus eliminating the need for replacement. In addition to CHMSL, some cars and motorcycles have replaced incandescent brake lights with LEDs in the main brake lights.
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