In recent years, with the continuous improvement of LED in almost all aspects such as light efficiency and cost, its application fields have been continuously expanded, from traditional portable device backlights to medium and large-sized LCD Display/LCD TV backlights, automotive and general lighting. . This article will specifically introduce various LED driver solutions suitable for automotive lighting applications and discuss some typical applications.
LEDs offer numerous advantages for automotive lighting applications
The applications of LEDs in automobiles are very broad, but can be simply summarized as interior lighting and exterior lighting (see Figure 1). Exterior lighting includes headlamps, tail lighting, etc., and interior lighting includes interior convenience and comfort lighting and instrument Panel backlighting.
Figure 1: Diverse automotive LED lighting applications
There are many factors driving the adoption of automotive LED lighting. Taking front lamps as an example, using LEDs as light sources has many advantages:
Facilitates flexible or novel form factors – LEDs are physically small and can be used to develop extremely compact, extremely thin modules. Compared to halogen and xenon lamps, multi-string LED modules require smaller and simpler lens and diffuser hardware. And the light of multiple LED light sources is easier to guide, which greatly reduces the impact of engineering design on modeling.
Light Intensity and Energy Efficiency Continue to Improve – LED light intensity is on an extremely fast ramp-up curve, showing a trend of doubling the luminous flux every 18 to 24 months. The light output of LED has exceeded that of halogen lamps, and the actual light efficiency performance of LEDs will be comparable to that of xenon lamps in the future.
High reliability and long life – as long as effective thermal management of the LED headlamp module keeps the junction temperature low and protects it from switch on/off, current spikes and battery pulses that can occur during dimming , it is not unrealistic to expect them to last throughout the life of the car.
Significant energy savings – LED headlamps use much less fuel/energy than other options. Using energy efficient smart power technology/chips instead of general ICs that require multiple external components can be more energy efficient.
As a result, LEDs are increasingly used in automotive lighting and are used by many automakers as a design selling point.
Comparison of LED driver solutions for automotive lighting
There are various applications of LEDs in automotive lighting, and different applications have different requirements for LED current. Therefore, it is necessary to select a suitable LED driver solution according to the specific application requirements.
A key function of an LED drive scheme is to regulate current over a wide range of operating conditions, regardless of input conditions and changes in forward voltage. The drive solution must meet application requirements in terms of energy efficiency, form factor, cost and safety. At the same time, the chosen solution must be easy to use and robust enough to adapt to the exacting environment of the specific application.
Typical LED driver solutions in automotive applications include resistive, linear LED drivers, switching LED drivers, and innovative lighting management LED drivers. In general, depending on the amount of LED current in the application, discrete components (i.e. resistors) or a linear drive scheme can be used for low current applications of 20 to 200 mA; for medium current applications of 200 to 500 mA, the choice of Linear or switching driver scheme; while in high current applications greater than 500 mA, the switching driver scheme is generally chosen.
In fact, resistors are the simplest and lowest cost LED current limiting solution, but they do not “regulate the current”, they are simply when the LED forward voltage changes and the input power supply voltage changes and causes the current to change, causing the LED brightness to vary. Limit LED maximum 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 than resistive solution at lower cost than linear or switching drivers, suitable for low current LED lighting applications with currents less than 200 mA. Inexpensive and robust, CCRs provide constant brightness over a wide voltage range, protect LEDs from overdrive at high input voltages, and still provide high 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. The CCR operates up to a maximum voltage of 50 V and can withstand battery load dumps. CCR provides different packages such as SOD123, SOT123 and DPAK, which can work in strict thermal environment (125℃), and the negative temperature coefficient characteristic protects the device itself and LED under high ambient temperature conditions. In addition, CCR does not generate electromagnetic interference and is easy to design.
Figure 2: Two-terminal and three-terminal CCR circuit diagrams.
Linear regulators support multiple line parallel configurations to spread heat dissipation, provide ±2% current regulation accuracy, have no electromagnetic interference (EMI) issues, and are moderately cost-effective but also less energy efficient. With the advantages of high energy efficiency and flexibility, switching regulators are widely used. This solution is more expensive and more technically complex, but also offers significant advantages, such as supporting any type of input voltage to output voltage relationship, and depending on the input/output conditions, the energy efficiency can be higher than 90%. Unlike linear drivers, they are sensitive to EMI, creating design constraints that designers need to be aware of.
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, can withstand up to 125 ℃ ambient temperature, used in automotive headlights, combination taillights and the latest Advanced Front Lighting System (AFS), etc. application, which will be discussed in detail later.
1) CCR for low current LED applications
ON Semiconductor has developed the NSI45 series of CCRs (see Figure 2) using patented Self-Biased Transistor (SBT) technology. This series of CCRs includes two-terminal fixed output and three-terminal adjustable output types, with current levels ranging from 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 suitable for high-side and low-side applications; it can drive one or more strings of LEDs with a single CCR, or drive one or more strings of LEDs with multiple CCRs in parallel (details See reference 1).
Figure 3: CCR Automotive Center High Mounted Stop Light (CHMSL) application circuit diagram.
2) Linear LED drivers for applications such as backlighting, interior lighting control, and taillights
In the linear driver solution, typical products include ON Semiconductor’s NUD4001 and NUD4011 linear LED drivers, the rated input voltage range of the two devices is 6 to 30 V and 48 to 200 V, respectively, and the rated output current is up to 500 mA and up to 70 V. mA, applications in automobiles include tail lights, direction lights, brake lights and dome lights. Both devices are designed to replace discrete solutions in AC-DC applications, allowing designers to set the drive current for different LED arrays using external resistors. 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 NUD4001 in a car parking light.
Figure 4: An application example of the NUD4001 in a car stop light.
In high-brightness LED automotive lighting applications that require driving high currents, ON Semiconductor’s CAT4101 high-brightness linear LED driver can be used. The CAT4101 can drive a string of high brightness LEDs up to 1 A with a very low 0.5 V drop at full load. This simple solution requires no inductors, eliminates switching noise, minimizes component count, and simplifies design.
3) Covers different configurations of LED switch drivers such as buck, boost and buck-boost
The energy efficiency of switching regulators that drive LEDs is generally between 50% and 90%, involving different topologies such as buck, boost, and buck-boost, and pays attention to EMI control methods. Lights, fog lights, daytime running lights and side marker lights and other applications. ON Semiconductor’s switching regulator products used in automotive LED lighting are shown in Table 1.
Among them, the typical boost Controller is such as 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. The device operates over a wide battery voltage range of 3.5 V to 40 V, is designed for -40°C to 150°C junction temperature, provides ±2.0% output voltage accuracy over operating temperature, and provides low shutdown current ( typically less than 10 μA) to help reduce power consumption.
In terms of step-down switch drivers, NCV8842, NCV8843 and NCV51411 are included, which are suitable for applications such as body/telematics systems. The NCV8842/3 are 1.5 A, 170/340 kHz step-down drivers with synchronization that support input voltages from 4.5 V to 40 V and output voltages programmable from 1.27 V. A sync pin function is used to improve EMI performance. NCV5141x (such as NCV51411 and NCV51413) is the version of CS5141x for automotive applications. It provides high energy efficiency. Under the condition of 9 to 15 V input voltage, the energy efficiency of driving 2 LEDs with a forward voltage drop of 3.5 V at 700 mA is basically higher than 85 %. Another automotive-grade synchronous buck controller supporting input voltages from 4.5 to 45 V offers greater than 93% efficiency even at wide load currents, with a maximum quiescent current of only 1 μA in sleep mode.
Table 1: ON Semiconductor’s switching regulator products for automotive LED lighting
In addition, ON Semiconductor also provides a variety of multi-topology switch drivers that can be used in automotive LED lighting, including NCV33063AV, NCV3065 and NCV3163. Among them, the NCV33063AV and NCV3065 both support a maximum current of 1.5 A and can be configured as buck, boost, SEPIC or buck-boost topologies, suitable for automotive interior lighting applications. The NCV3065 can also be used for interior lighting, targeting very cost-sensitive applications, and can be configured as a controller if higher currents are required. The NCV3163 is a 3.4 A maximum current monolithic switching regulator that enables system designers to apply buck, boost or buck-boost (voltage inversion) topologies with a minimum number of external components.
4) Highly integrated lighting management IC for applications such as headlamps and combination tail lamps
Automotive headlights include different segments, such as daytime running lights (DRL), low and high beams, signal lights and fog lights. The earliest application of LEDs in headlights was the daytime running lights. As the cost of high-brightness LEDs continues to decrease and performance continues to improve, more and more new car designs are using LEDs more widely in other headlight fields, such as low beam and high beam, signal lights and fog lights. Even LEDs are used to provide emerging features such as beam shaping and motorway spot.
In general, automotive headlights are required to support from a single LED to multiple strings of LEDs, with voltages up to 60 V; in addition, they also require support for pulse width modulation (PWM) dimming (such as for position lights), high integration, High energy efficiency, low electromagnetic radiation of LED strings, integrated diagnostics and communication interfaces, etc. ON Semiconductor has developed the NCV78663 power ballast and dual LED driver 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, provides greater than 90% overall energy efficiency, drives multiple strings of LEDs up to 60 V, and can be dimmed with PWM Maintaining color temperature and controlling average current allows designers to control high and low beams, daytime running lights, turn indicators, and fog lights from a single, highly integrated SoC with minimal external components. The device communicates with an external microcontroller via an SPI interface, dynamically controls system parameters, detects LED operating status, and feeds back diagnostic information after power-up. Figure 5 shows the circuit diagram of the NCV78663 in an advanced automotive headlamp application.
Figure 5: a) Application example of automotive LED headlamp; b) Application circuit diagram of automotive LED headlamp based on NCV78663.
For automotive taillight applications, low-cost and low-current LED drive solutions such as CCR can be used according to different application requirements, or high-integration level solutions that provide higher performance and higher energy efficiency levels can be used, such as ON Semiconductor. The highly integrated linear current regulation and controller NCV7680. This device contains 8 linear programmable constant current sources, which are designed for current regulation and control of automotive combination tail lights, and each channel can output up to 75 mA of LED drive current. The NCV7680’s high level of functional integration allows engineers to easily implement two brightness levels, one for parking and the other for tail lighting. Optional PWM control can also be applied if desired. Designers need only one external resistor to program the output current of all channels. The operating temperature range is −40°C to +150°C.
Figure 6: a) Legend of LED combined tail light; b) Application circuit diagram of NCV7680 in LED combined tail light.
GreenPoint® Online Design Simulation Tool Accelerates Automotive LED Lighting Design
As the premier supplier of high-performance silicon solutions for energy-efficient Electronic products, ON Semiconductor provides complete system solutions for automotive LED lighting applications, including power supplies, MOSFETs, rectifiers, protection, filters, and thermal management products. In addition, to help designers speed up LED lighting design, ON Semiconductor also provides the GreenPoint® online design simulation tool, allowing designers to sit at the bench and easily go through “select LED drivers”, “determine design requirements”, Several steps such as “automatically generate design circuit diagram”, “simulation and verification”, “generate bill of materials and report”, “download report as PDF file” and “save file and share” greatly shorten the development time and speed up the process of product launch.
This online design tool has currently supported the application design of a number of ON Semiconductor’s high-efficiency LED driver products. The supported automotive LED drivers include a variety of devices in the NSI45 series, and more products will be supported in the future.
With the continuous improvement of performance and cost reduction of LED performance, the application fields in automotive interior and exterior lighting are getting wider and wider. Designers need to select the appropriate LED driver solution for the specific application, such as linear constant current regulator, linear regulator or switching regulator. As the premier supplier of high-performance silicon solutions for energy-efficient electronics, ON Semiconductor offers a complete line of AEC Q100-qualified LED drivers for automotive lighting, from low to high current, including recently introduced The series of highly integrated and energy-efficient lighting management integrated circuits facilitate designers to select suitable automotive LED driver solutions according to specific application requirements.
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