LED technology has been slowly making its way into automotive businesses for years. LEDs have improved in terms of brightness, efficiency, and cost. While automotive lighting has made driving safer, it has also introduced some sophisticated and intricate electronic changes that pose design issues. Let's have a look at the fundamentals of automotive lighting as well as the most recent innovations that have an impact on design.
What are the Benefits of Using LEDs in Automotive Applications?
There are two main reasons behind this. To begin with, LEDs are more energy-efficient than traditional incandescent bulbs. For the same or greater illumination intensity, they use less power. LEDs are six times more efficient than the incandescent bulbs they replace, according to tests.
Second, compared to an incandescent bulb, LEDs have a longer service life. After 1,200 hours of operation, headlights, taillights, and other lights burn out. And, in most cases, replacement is prohibitively expensive. The typical LED lasts 42 times longer than an incandescent bulb. You may never need to replace a light source in your vehicle because it has a service life of over 50,000 hours.
The ABCs of Automotive Lighting
There are three types of car lighting applications: external front, exterior rear, and inside. The focus of this paper will be on outdoor lighting. Headlights, high and low beams, daytime running lights (DRLs), fog lights, and turn signals are all part of the front exterior lighting system. Adaptive headlamp lighting is also available on some vehicles, allowing for enhanced illumination around bends while driving in low-light settings.
Taillights, stop lights, backup lights, and a license-plate light make up the rear lighting. Depending on the manufacturer, there may also be extra ornamental or style lights. In any case, power consumption can be substantial with a full complement of front and rear LED lights. However, this is less energy than is consumed by older incandescent lights.
Individual LEDs are joined together to form a matrix or cluster in automotive lights. The majority of automotive LEDs are white, however red and amber LEDs in various sizes and light intensities are also available. Light guides, lenses, and diffusers are employed to make the light appear to come from a single source, removing the individual dot appearance of early LED automobile light fixtures.
To operate the LEDs, special drivers are required. A cluster of numerous LEDs may usually be handled by a single driver IC. Current sources with the proper drive and interface circuits serve as the drivers. A series string of LEDs is a common configuration, with all LEDs receiving the same current. This is necessary to verify that the lights are of the same color and brightness.
LED drivers are dc-dc converters and regulators. They are powered by the car's 12-volt system and can deliver a lower or higher dc output depending on the situation. Buck and boost types, as well as buck-boost, SEPIC, and Cuk are all common. The drivers are connected to a master control MCU, and the control signals are sent around the car using a CAN interface network as needed.
Lighting in the Front and Back
On all cars, the front lighting is largely fixed and similar—headlights, DRLs, and turn signals are all required and standardized. Of course, special drivers are required. Dimming and adaptable front lighting are two of the most recent advances (AFL). Pulse-width modulation is used to dim the light to avoid blinding oncoming vehicles (PWM).
AFL is made up of two extra lights that are usually located to the left and right of the headlights. These lights give additional side illumination for safe nighttime turning. The AFL units switch on and move to direct the light to the side as the steering wheel is turned to the right or left. For this, stepper motors are widely employed. The lights can be adjusted up and down to avoid obstructing incoming motorist vision.
When it comes to rear illumination, things are a little different. While tail lights, stop lights, and backup lights are all necessary, the back of the car has become a blank canvas for designers to experiment with new ideas. Vehicle manufacturers enjoy creating a distinctive style or symbol that identifies a specific make or model. Some vehicles may have a distinctive appearance that is enhanced by a creative light show or operation. Lighting that spans across the full back of the car is a contemporary trend.
manufacturers seek pixel-level control, where a pixel is one LED, which would allow for a multitude of tail-light animations, which is becoming increasingly appealing. This feature is now available thanks to newly released drivers. Rear-lighting systems are influenced by three trends: complicated animation, evolving lamp styles, and diagnostics. To discover more, click on the following links.
The Automatic Lighting System (ALS)
The body control module (BCM) and LED drivers are two pieces of equipment that make up older classic vehicle lighting systems (see figure, a). The BCM is a microcontroller-based electronic block that controls all or most of the electrical and electronic systems related to the vehicle's body, such as doors, windows, mirrors, seats, and lights. Individual light drivers are controlled by the BCM.
The MCU in the body control module is used to control the older LED driver circuits (a). The body control module now delivers commands to the electronic control unit in newer configurations (b). The drivers for the LEDs are housed in the ECU.
The BCM plus a separate electronic control unit make up the contemporary version (ECU). The LED drivers are housed in the ECU (see figure, b). The drivers are controlled by the BCM's MCU via the ECU's MCU. A controller-area-network (CAN) bus connects the BCM with the ECU for communication.
Design Technical hurdles
Engineers working on automobile lighting systems encounter a number of difficulties. The following are the main concerns affecting the design of the drivers and their packaging:
Operating from the 12-volt car battery power bus, which can have voltages as low as 6 volts during start-stop restarts or as high as 16 volts during alternator charging. Transients or pulses that peak at 36 V during a load dump are another issues.
Operating over a wide temperature range, ranging from 40 to + 85°C in most cases.
Provide fault diagnosis, which is extremely useful considering the complexity of today's lighting systems.
Complying with EMI/EMC regulations. LED drivers are a type of switch-mode power supply that produces a lot of noise. It is critical that automobiles do not interfere with other vehicles or electrical equipment in the vicinity. Lighting systems are typically examined by the Comite' International Special des Perturbations Radio'electriques (CISPR) 25 and to noise-immunity standards like ISO 11452-5.
Texas Instruments has a series of LED drivers and support circuits that can help you overcome these obstacles in your design.
Examples of LED Drivers
Texas Instruments' TPC929120-Q1 is representative of the current generation of LED drivers. It works with a supply voltage of 4.5 to 40 volts and a temperature range of 40 to + 125 degrees Celsius. The AEC-Q100 approved driver satisfies the demands of current pixel-level control and diagnostics trends. 12 separate output channels with 40-V high-side drivers, 8-bit output-current selection, and 12-bit PWM duty-cycle selection are among the highlights. PWM can be used to dim each of the 12 channels separately.
The built-in diagnostics and protection is a nice new feature. The IC can detect open or shorted LEDs, among other things, and it also protects against overvoltage and overheating. The internal FlexWire serial data interface communicates over normal CAN physical-layer wiring, allowing for long-distance cable runs without producing interference in the car.
Other driver ICs are also available to meet the needs of future headlights. A dual-stage power supply for high-power LEDs is commonly used in headlights. The TPS92682-Q1 LED Driver can be used for the first stage. It may be used as a constant-current buck-boost/boost/SEPIC LED driver for static lamps or as a constant-voltage boost regulator for adaptive systems, and it's very programmable. The TPS92520-Q1 monolithic buck LED driver, which dims via analog or PWM control, can power the second stage. It has a switching frequency of up to 2.2 MHz with an exposed topside pad on the package, which eliminates many of the thermal issues that can arise in headlight design. SPI is used to communicate between the two devices.
Furthermore, by enabling individual pixel-level LED control, the TPS9266x-Q1 series of LED matrix managers provides fully dynamic adaptive-lighting solutions. Four sub-strings of three series-connected integrated switches for bypassing specific LEDs are included in the matrix management. Other switching arrays allow for a wide range of pixel control functions.
Reference Designs that are currently available
The reference design from TI is a fantastic place to start when designing a static or adaptive headlamp. This reference design for a 120-W matrix-compatible headlight electronic-control-unit (ECU) includes a heat-sink metal shell and CISPR 25 Class 5 performed test data, allowing you to create a thermally efficient headlight ECU. The TPS9282-Q1 and TPS92520-Q1 LED drivers are used in the reference design, which is helpful for driving pixel-controlled LED loads.