Various LED driver solutions and applications for automotive lighting applications

In recent years, with the continuous improvement of LED in almost every aspect such as light efficiency and cost, its application fields have been continuously expanded, from the traditional portable device backlight to the medium and large size LCD display / LCD TV backlight, automotive and general lighting, etc. . This article will focus on various LED driver solutions for automotive lighting applications and explore some typical applications.

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LEDs offer many advantages for automotive lighting applications

LEDs are used in a wide range of applications in automobiles, but can be easily summarized into internal and external lighting (see Figure 1). Exterior lighting is like headlights, taillights, etc. Interior lighting includes interior convenience and comfort lighting and dashboard backlighting.

Figure 1: A wide range of automotive LED lighting applications

There are many factors driving automotive LED lighting applications. For example, in the case of a previous lamp, the use of LED as a light source has many advantages:

Convenient for flexible or novel design – LEDs are physically small and can be used to develop extremely compact, extremely thin modules. Multi-string LED modules require smaller, simpler lens and light diffuser hardware than halogen and xenon lamps. And the light of multiple LED light sources is easier to guide, greatly reducing the impact of engineering design on the shape.

Light intensity and energy efficiency continue to increase - LED light intensity is on an extremely fast lifting curve, showing a trend that the luminous flux will double every 18 to 24 months. The LED light output has exceeded the halogen lamp, and the actual LED performance of the LED will be comparable to that of the Xenon lamp.

High reliability and long life – as long as the LED headlamp module is effectively thermally managed to maintain a low junction temperature and protect it from switching on/off, current spikes and battery pulses during dimming It is not unrealistic to expect them to continue to be used throughout the life of the car.

Significant energy savings – LED headlamps use much less fuel/energy than other solutions. Using energy-efficient smart power technology/chips instead of general ICs that require multiple external components can be more energy efficient.

Therefore, the application of LED in automotive lighting is increasing, and it is regarded as a design selling point by many automobile manufacturers.

Comparison of LED driver solutions for automotive lighting

LEDs are widely used in automotive lighting. Different applications have different LED current requirements. Therefore, it is necessary to select a suitable LED driver solution according to specific application requirements.

One of the main functions of the LED drive scheme is to stabilize the flow under a variety of operating conditions, regardless of input conditions and how the forward voltage changes. The drive solution must meet the application requirements for energy efficiency, form factor, cost and safety. At the same time, the chosen solution must be easy to use and strong enough to adapt to the strict environment of the particular application.

Typical LED driver solutions in automotive applications include resistors, linear LED drivers, switch LED drivers, and innovative lighting management LED drivers. In general, depending on the amount of LED current in the application, discrete components (ie, resistors) or linear drive schemes can be used in low current applications from 20 to 200 mA; in medium current applications from 200 to 500 mA, optional Linear or switch driver solutions; in high current applications greater than 500 mA, the switch driver scheme is typically chosen.

In fact, resistors are the simplest and lowest cost LED current limiting solution, but they are not “steady flow”, but simply when the LED forward voltage changes and the input supply voltage changes and causes a current change that causes LED brightness variation. Limit the maximum LED current. Although the cost of this solution is low, the energy efficiency is also the lowest, and there are problems such as LED screening cost and thermal runaway.

CCR is a higher performance but lower cost solution than a linear driver or switch driver for low current LED lighting applications with currents less than 200 mA. CCR is inexpensive and rugged, provides constant brightness over a wide voltage range, protects the LED from overdriving when the input voltage is high, and still provides higher brightness at low battery voltages. This solution can reduce or eliminate the inventory generated by LED screening, making the total cost of the solution lower. With a maximum operating voltage of 50 V, the CCR can withstand battery load sags. CCR offers different packages such as SOD123, SOT123 and DPAK, which can operate in a severe thermal environment (125 °C), and the negative temperature coefficient characteristic protects the device itself and the LED under high ambient temperature conditions. In addition, CCR does not generate electromagnetic interference and is easy to design.

Figure 2: Double-ended and three-terminal CCR circuit diagram.

The linear regulator supports multiple lines in parallel configuration to spread heat dissipation, providing ±2% steady current accuracy, no electromagnetic interference (EMI) problems, medium cost, but low energy efficiency. Switching regulators are widely used due to their high energy efficiency and flexibility. This solution is more costly and more complex, but it also offers significant advantages, such as supporting any type of input voltage to output voltage relationship, and energy efficiency can be higher than 90% depending on input/output conditions. Unlike linear drivers, they are sensitive to EMI and give designers design constraints that require attention.

It is worth mentioning that in addition to these common LED driver solutions, ON Semiconductor has introduced a highly integrated LED lighting management integrated circuit (IC). These lighting management integrates a variety of LED drive and control functions, equivalent to a complete subsystem capable of withstanding ambient temperatures up to 125 ° C for automotive headlamps, combined taillights and the latest advanced headlamp systems (AFS) Application, which will be discussed in detail later.

Typical automotive application LED driver products and their applications

1) CCR for low current LED applications

ON Semiconductor has developed the NSI45 Series CCR using patented self-biased transistor (SBT) technology (see Figure 2). This series of CCRs includes two types of dual-ended fixed output and three-terminal adjustable output, and the current level covers 10 to 180 mA. The three-terminal adjustable output CCR includes different options such as current 30 to 80 mA (SOT-223) and 60 to 150 mA (DPAK), which can be used to meet specific current setting requirements.

CCR is easy to design and is suitable for high-side and low-side applications; it can drive one or more strings of LEDs with a single CCR, or drive multiple strings of LEDs in parallel with multiple CCRs (detailed See reference 1).

Figure 3: CCR car central high stop lights (CHMSL) application circuit diagram.

2) Linear LED drivers for backlighting, interior lighting control and taillight applications

In linear driver solutions, typical products include ON Semiconductor's NUD4001 and NUD4011 linear LED drivers, which are rated for input voltages ranging from 6 to 30 V and 48 to 200 V, respectively, and rated output currents up to 500 mA and up to 70 mA, in automotive applications include taillights, directional lights, brake lights and roof lights. Both devices are designed to replace discrete solutions in AC-DC applications, allowing designers to use external resistors to set drive currents for different LED arrays. The difference is that the NUD4001 is suitable for low voltage applications of 5 V, 12 V or 24 V, while the NUD4011 supports up to 200 V. Figure 4 shows the application of the NUD4001 in a car parking light.

Figure 4: Example of the application of the NUD4001 in a car parking light.

In high-brightness LED automotive lighting applications that require high currents, ON Semiconductor's CAT4101 high-brightness linear LED driver can be used. The CAT4101 can drive a string of high-brightness LEDs with currents up to 1 A, and the voltage drop at full load is only a very low 0.5 V. This simple solution eliminates the need for inductance, eliminates switching noise, minimizes component count, and simplifies design.

3) LED switch drivers for different configurations including buck, boost and buck-boost

Switching regulators that drive LEDs typically range in energy efficiency from 50% to 90%. They involve different topologies such as buck, boost, and buck-boost. They focus on EMI control methods and are used primarily for automotive interior lighting and parking. Applications such as lights, fog lights, daytime running lights and side marker lights. The switching regulator products used by ON Semiconductor for automotive LED lighting are shown in Table 1.

Among them, the typical boost controller is like NCV8871. This is a boost controller with a multi-function enable/sync (SYNC) pin that can be synchronized with an external clock to drive an external N-channel MOSFET. Operating from a wide battery voltage range of 3.5 V to 40 V, this device is designed for junction temperatures from -40 ° C to 150 ° C, provides ±2.0% output voltage accuracy over operating temperature and provides low turn-off current ( Typical values ​​are less than 10 μA) to help reduce power consumption.

In terms of buck switch drivers, including NCV8842, NCV8843 and NCV51411, it is suitable for applications such as body/television systems. The NCV8842/3 is a 1.5 A, 170/340 kHz step-down driver with synchronization that supports an input voltage of 4.5 V to 40 V, while the output voltage can be programmed from 1.27 V. The sync pin function is used to improve EMI performance. The NCV5141x (such as the NCV51411 and NCV51413) is a version of the CS5141x for automotive applications that provides energy efficiency and drives two forward voltage drops of 3.5 V at 700 mA at 9 to 15 V input voltage. %. Another automotive-grade synchronous buck controller that supports 4.5 to 45 V input voltage delivers greater than 93% efficiency even at wide load currents and a maximum quiescent current of only 1 μA in sleep mode.

Table 1: Switching Regulator Products for ON Semiconductor Applications for Automotive LED Lighting

In addition, ON Semiconductor offers a variety of multi-topology switch drivers for automotive LED lighting, including the NCV33063AV, NCV3065 and NCV3163. The NCV33063AV and NCV3065 support up to 1.5 A and can be configured in buck, boost, SEPIC or buck-boost topologies for automotive interior lighting applications. The NCV3065 can also be used for internal lighting for cost-sensitive applications and can be configured as a controller if higher current is required. The NCV3163 is a monolithic switching regulator with a maximum current of 3.4 A, allowing system designers to apply buck, boost or buck-boost (voltage reversal) topologies with a minimum number of external components.

4) Highly integrated lighting management IC for applications such as headlamps and combination taillights

The headlights of the car include different subdivisions such as daytime running lights (DRL), low beam and high beam lights, signal lights and fog lights. The earliest application of LEDs in the headlights is the daytime running lights. As the cost of high-brightness LEDs continues to decrease and performance continues to increase, more and more new car designs are increasingly using LEDs in other headlamp fields, such as low beam and high beam, signal lights and fog lamps. Even LEDs provide emerging functions such as beam shaping and motorway spot.

In general, automotive headlamps require support from a single LED to multiple strings of LEDs up to 60 V; in addition, pulse width modulation (PWM) dimming (eg for position lights), high integration, High energy efficiency, LED string low electromagnetic radiation, integrated diagnostics and communication interface. ON Semiconductor has developed the NCV78663 power ballast and dual LED drivers for LED automotive headlamp systems. The NCV78663 is an advanced, highly reliable, energy-efficient, system-on-chip (SoC) LED driver that supports up to 2 A current, delivering over 90% total energy efficiency, driving multiple strings of LEDs up to 60 V, and PWM dimming Maintaining color temperature and controlling average current allows designers to control high beam and low beam, daytime running lights, turn indicators and fog lights with a highly integrated SoC with minimal external components. The device communicates with an external microcontroller via the SPI interface, dynamically controlling system parameters, detecting LED operating conditions, and feeding back diagnostic information upon power up. Figure 5 shows the circuit diagram of the NCV78663 in an advanced automotive headlamp application.

Figure 5: a) Automotive LED headlamp application diagram; b) NCV78663 based automotive LED headlamp application circuit diagram.

For automotive taillight applications, low-cost, low-current LED drive solutions such as CCR can be used depending on the application requirements, or high-level-level solutions that offer higher performance and higher energy efficiency levels, such as ON Semiconductor Highly integrated linear current stabilization and controller NCV7680. The device includes an 8-track programmable constant current source designed for steady current and control of automotive taillights with up to 75 mA of LED drive current per channel. The NCV7680's highly integrated functionality allows engineers to easily achieve two brightness levels, one for parking and the other for tail lighting. Optional PWM control can also be applied if desired. Designers only need an external resistor to set the output current of all channels. Operating temperature range is −40°C to +150°C.

Figure 6: a) LED combination taillight legend; b) NCV7680 application circuit diagram in LED combination taillights.

GreenPoint® online design simulation tool accelerates automotive LED lighting design

As the premier supplier of high-performance silicon solutions for energy-efficient electronics, ON Semiconductor offers complete system solutions for automotive LED lighting applications, including power supplies, MOSFETs, rectifiers, protection, filters and thermal management products. In addition, to help designers accelerate LED lighting design, ON Semiconductor also offers GreenPoint® online design simulation tools that allow designers to easily “select selected LED drivers” and “determine design requirements” by sitting in front of the workbench. Several steps, such as “automatically generate design circuit diagrams”, “simulation and verification”, “generate bills of materials and reports”, “download reports as PDF files” and “save files and share”, significantly shorten development time and speed up product launch.

This online design tool currently supports a variety of applications for ON Semiconductor's energy-efficient LED driver products, including LED drivers for automotive applications, including a number of devices in the NSI45 family, and will support more products in the future.

to sum up:

As LED performance continues to improve performance and cost continues to decrease, applications in automotive interior and exterior lighting are becoming wider and wider. Designers need to choose the right LED driver solution for their application, such as a linear constant current regulator, a linear regulator, or a switching regulator. As the premier supplier of high-performance silicon solutions for energy-efficient electronics, ON Semiconductor offers a complete line of LED drivers for automotive lighting, AEC Q100-certified, from low current to high current, including new releases The series of highly integrated, energy-efficient lighting management ICs make it easy for designers to choose the right automotive LED driver solution for their specific application requirements.

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