Analysis of the current status and solutions of automotive LED lighting systems

In today's mid-range and high-end cars, modern lighting concepts are being interpreted more and more vividly. Both exterior and interior lighting are stylish and personalized, and mood setting modes are used in different parts of the car to control the light color and brightness of the "personal space" , such as the space under the driver's feet or the backlight of the console. This type of automotive lighting uses new light sources, which not only enriches the consumer experience, but also meets the requirements of environmental protection and energy saving.

To realize advanced automotive lighting applications, corresponding semiconductor technology must be supported. As a leading automotive lighting solution provider, ON Semiconductor has been providing a variety of general and dedicated high-efficiency device solutions for automotive lighting applications, meeting the strict requirements of automotive applications and meeting the rapidly developing market needs.

Modern car lighting systems

In recent years, light-emitting diodes ( LEDs ) have been widely adopted in automotive lighting applications. Compared with incandescent lamps, LED-based lighting systems have longer service life, lower power consumption, and greater design flexibility. These characteristics make them very suitable for automotive interior lighting applications. In addition, as technology continues to advance, white light LEDs with lower costs and higher light output per watt have emerged , making LEDs more suitable for various lighting applications in automotive interiors.

LEDs are widely used in automobiles. For example, they can be installed in the roof interior or in the lower door interior to focus light on specific areas inside and outside the car. LEDs can also be integrated near door handles, keyholes, pedals, cup holders, or as turn signal lights on rearview mirrors. The shape of the light indicator can be very simple or very exquisite to meet the requirements of precise lighting, providing convenience and beauty for people, as shown in Figure 1.

Figure 1: Various automotive lighting applications.

Advanced Automotive Lighting Solutions from ON Semiconductor

ON Semiconductor has been providing standard products and customized devices for automotive lighting applications, including general bulb driver solutions, as well as stepper drivers, LED drivers , and high-intensity discharge lamp (HID, such as xenon lamp) drivers. In the HID driver application-specific integrated circuit (ASIC ) market, the headlamp level adjustment and rotation stepper drivers developed by ON Semiconductor have been widely adopted by the industry. In the automotive LED lighting market, ON Semiconductor provides a rich product portfolio for in-vehicle and out-of-vehicle applications. In the automotive lighting system block diagram shown in Figure 2, ON Semiconductor has a variety of corresponding products. Several major solutions are introduced below.

Figure 2: Automotive lighting system block diagram.

1. Headlight Stepper motor Driver

Most cars today are equipped with halogen lamps with high beam (HB) and low beam (LB) functions, which are the main functions of headlights. High beam halogen lamps typically consume 55 W and have a light output of about 1,000 lumens. HID technology has been around for more than a decade, with a power consumption of about 35 W and a light output of about 3,500 lumens , which has certain application advantages. Over time, HID lamps have integrated high beam functions into bi-xenon lamp solutions. However, some countries require automatic adjustment of the height of low beam lamps because the high brightness and glare of HIDs affect the vision of approaching vehicles.

Another important aspect of automotive headlights is the beam rotation of the Advanced Front Lighting System (AFS) to optimize the visibility curve, while the Adaptive Driving Beam (ADB) function adjusts the beam according to real-time conditions. Stepper motors are the preferred controller for AFS and ADB .

The AMIS-30623 single-chip bipolar stepper motor driver from ON Semiconductor is suitable for horizontal adjustment and rotation control of headlights. The device comes with an integrated position controller and a local interconnect network (LIN) interface , which enables the design of a dedicated mechatronic solution that can be remotely connected to a LIN host, as shown in Figure 3. It receives position commands through the bus using configurable parameters such as current, speed, acceleration, and deceleration, and drives the motor coil to the desired position. The AMIS-30623 can also detect motor stalls.

The device embeds a dedicated finite state machine and a LIN command set customized for advanced headlight system requirements. It also integrates sensorless step failure detection function, which can improve reliability, reduce component count and board space, and reduce product cost.

Figure 3: Headlamp leveling and rotation circuit using AMIS-0623.

2. LED headlight system Power supply Ballast and dual LED driver

Currently, most cars still use halogen headlights to provide high and low beam functions, but the future trend is to use xenon lamps and LED lamps . In particular, the application of LED lamps, which can significantly reduce the power consumption of headlights, will rise rapidly, and 30% of cars will be equipped with multiple LED headlight functions within 5 years. LED lighting provides a more fashionable option, enables "instant" lighting, and allows brightness control from 0% to 100% power .

The NCV78663 single-chip smart headlamp LED driver from ON Semiconductor is a new device that will be released in 2011. It supports single-module control of high beam, low beam, daytime running lights, position lights, turn signals and fog lights. With integrated digital dimming, programmable serial peripheral interface (SPI) settings and built-in diagnostic functions, the NCV78663 provides an integrated and comprehensive energy-efficient solution for headlamp control.

Figure 4: The NCV78663 single-chip smart headlight LED driver.

NCV78663 adopts buck/boost topology, and only a few external components are needed to achieve LED current regulation, constant current sharing, efficient integrated buck switch (high side), and up to 2 A current; its extended diagnostic functions include: detection of open circuit or failing driver, short circuit, overcurrent protection, and single LED failure. In addition, the device also has thermal protection, system customization through SPI interface and/or OTP settings, multiple system configurations with one device, better EMC performance without additional filtering, low battery EMC, and low LED string EMC. Using NCV78663 can reduce the number of external components and the total energy efficiency is higher than 90%. The evaluation board of this device has been launched, see Figure 5.

Figure 5: NCV78663 evaluation board.

3. HID headlamp full-function ASIC

The advent of HID lamps has improved the performance of headlamp systems. Compared with traditional halogen lamps, HID has improved color rendering, low power consumption, longer service life and higher light output. In order to support advanced functions, HID headlamps require highly efficient ballasts and complex control circuits.

The ON Semiconductor HID lamp control system is a hybrid analog/digital solution using an 8-bit microcontroller or a dedicated state machine, see Figure 6. The device integrates a DC/DC controller, as well as rich diagnostic functions (overvoltage, undervoltage, temperature sensor , life counter), various communication interfaces (LIN, SPI), and supports 35 W (D1/D2/D3/D4) and 25 W (D5) lamps.

Figure 6: Full-function ASIC for HID headlights.

4. Linear current stabilization and controller for automotive LED combination taillights

At present, more and more automobile combination taillights (RCL) are using LED lamp body groups, which are not only beautiful in appearance and high in light efficiency , but also help the following vehicles to clearly see the driving status of the front vehicle.

ON Semiconductor's NCV7680 is a linear current regulator and controller that can power combination taillights with a single chip, providing better performance and higher energy efficiency, and a smaller footprint than the solutions on the market. The device includes 8 linear programmable constant current sources, suitable for current regulation and control of automotive solid-state combination taillights (RCL), supporting up to 75 mA per channel light-emitting diode (LED) drive current.

The NCV7680 integrates many features to support two brightness levels, one for parking and the other for tail lighting. Optional pulse width modulation ( PWM ) control is also available if needed. System designers only need to use one external resistor to set the output current (overall set point). In addition, for designs requiring high current, optional external ballast field effect transistors (FETs) can distribute power according to the high current required by the design. The delayed power limit reduces the drive current in overvoltage conditions. This is very important for low current applications without external FETs.

Typical applications of this device include combination taillights, daytime running lights (DRL), fog lights, center high-mounted stop light (CHMSL) arrays, turn signals and other external modulation applications, liquid crystal display ( LCD ) backlights, lighting modules, etc. Compared with discrete solutions, this device can better match LED outputs, and the open-drain output function can be used to diagnose open LED strings, making it easy to find faults.

Figure 7: Application circuit using external FET transistor ballast.

Summarize

ON Semiconductor has been using its advanced automotive process technology to provide a variety of standard products and customized devices for automotive lighting applications. In addition to the solutions introduced above, there are also industry-leading products and solutions such as LED drivers using linear and switching power supplies (SMPS), LED current regulators, and central high-mount brake light constant current regulators.

Like various automotive application products that use advanced automotive process technology, all of these integrated circuits comply with automotive reliability, temperature and other regulatory and environmental requirements. At the same time, they can meet people's increasingly high requirements for interior lighting control, headlights, rear combination lights, fog lights, clearance lights, and especially new light sources, allowing drivers to fully experience the comfort and fun brought by lighting.