In the past decade, automotive electronics products have developed by leaps and bounds, and in-vehicle electronic control, in-vehicle information services, and entertainment systems have significantly improved both in quantity and in fineness.
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 was the Central Overhead Parking Light (CHMSL); these LED and LED control card applications use red LEDs to provide a very flat, light-emitting array that is easy to install and never needs to be replaced.
Traditionally, incandescent bulbs are the most economical source of light and are still used by many cars. However, as the available lighting space shrinks and the life expectancy of lighting sources continues to increase, the color and design of the lights provided by LEDs is rapidly replacing incandescent bulb applications. Even traditional CCFL TFT-LCD backlight applications are gradually being replaced by white LED arrays.
What's more, people are still using an electric "steerable" high-current LED array to develop headlights, which has been dominated by halogen/æ°™ filament design. Almost all automotive lighting applications, including interior/external lighting and backlighting applications, will gradually transition to LED adoption. The benefits of using LEDs have many positive implications. First (and perhaps the most important), it never needs to be replaced because its 100,000-hour solid-state life (service life: 11 and a half years) is longer than the car's life. This allows automakers to permanently embed them in the lighting system in the cabin without the need to have an inlet for replacing the filament bulb as in the past. Since the LED control card illumination system does not require the installation depth or area required for incandescent bulbs, it can also cause significant changes in the shape of the car. Another advantage of LED lighting and LED control card systems is their low power consumption, which results in reduced fuel consumption.
Automotive LED lighting design parameters
To ensure optimum performance and long operating life, LEDs require an effective drive circuit for both LED control cards. These LED control card drive circuits must be able to draw operating power from a fairly demanding automotive power bus, and should also be cost and space "efficient." In order to maintain its long working life, the current and temperature limits of the LED must not be exceeded.
In applications with a single LED to three (series) LEDs, a step-down LED control card will be required to reduce the car bus voltage (nominally 12V) to a more suitable LED voltage, depending on the application's LED Depending on the color and brightness requirements, the LED voltage can vary from 2.68V to 4.88V (each LED). In contrast, in applications such as brake lights that require multiple LED strings consisting of up to eight LEDs in series, the required output voltage is 21V to 39V, so a boost LED control card is required.
To produce a constant LED brightness with irregular input voltages, a constant current source must be obtained from these LED control card ICs. An internal sense resistor is used to monitor the output current for accurate current regulation. A wide dimming range is achieved by maintaining high output current accuracy over a wide current range (35 mA to 1 A). In many applications (especially for backlighting and interior lighting), dimming control may be required, requiring the LED control card to provide a simple method for adjusting the output current/LED brightness. With a suitable LED control card, the dimming operation can be done with a PWM signal, DC voltage or an external NMOS transistor with a dimming range of up to 3000:1.
Dual LED application
Many embedded high current LED applications will include single or two high current (ILEDs ranging from 1A to 1.5A) LEDs. These applications include interior lighting (eg, roof lights, map lights, storage box lights) and exterior lighting (eg, door sill lights or "ground lighting" lights). Depending on the application, they can be colored LEDs (for backlighting of in-vehicle instruments) or white LEDs (for general lighting). Since these LEDs typically 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.
Dual, 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 LEDs that require up to 1.5A. 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 is independently maintained in a wide current range of 50mA to 1.5A. High output current accuracy, and the unique circuit provides a 3000:1 dimming range without any color shift (this is common in LED current dimming).
The LED control card uses high-voltage side detection to achieve the ground connection of the LED negative, eliminating the need for a ground wire in most applications. It also has an integrated boost diode for each channel, further reducing the footprint and cost of the solution. Additional features include LED open and short circuit protection.
brake light
To date, the most common application of LEDs in automobiles has been the Central Overhead Parking Light (CHMSL). By the end of 2006, at least 60% of the cars had LED-type CHMSL installed. Benefits include faster lighting speeds, higher efficiency, longer working life, and a very thin red LED array with ease of design/installation. LEDs can achieve full illumination in less than 1ms (compared to traditional bulbs can take up to 200ms to produce their maximum brightness), so that the driver of the rear vehicle will greatly reduce the time to identify the brake lights, thereby reducing The probability of a rear-end collision accident.
Moreover, compared with incandescent bulbs, power consumption has also dropped by as much as 80%, ultimately contributing to fuel consumption. Its effective service life will easily exceed the life of the vehicle, thus eliminating the need for replacement. In addition to CHMSL, some cars and motorcycles also replace incandescent brake lights with LEDs in the main brake lights.
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