Solving EMI Challenges in LED Headlamps
January 26, 2017
|By: Tamer Kira
Director, Automotive, Maxim Integrated
Whether lighting your path down a dark road or making your car more visible to other drivers, high-brightness (HB) light emitting diodes (LEDs) are enhancing safety while reducing energy consumption. Ever since Audi became the first to use LEDs in its headlamps in 2004, automakers have been taking advantage of their compact size in an array of stylistic designs.
The market for HB LEDs is projected to exceed revenue of USD 22 billion by 2023, according to Global Market Insights, and the automotive industry’s share of this market is expected to grow steadily. Compared to traditional lighting technologies, the LEDs can save 50-70% of the energy use, reducing carbon emissions. With lifetimes of 50,000 hours or more, they last longer than other lighting technologies. This is useful for applications like daytime running lights. Also, LEDs turn on and off faster than incandescent lamps, which makes them ideal for brake lights.
Designing with HB LEDs, however, is not without challenges—one of the toughest being electromagnetic interference (EMI). These unwanted noise signals, which stem from the high switching frequency of the LED drivers, can degrade circuit performance or, if severe, inhibit circuit function. EMI can also wreak havoc on other vehicle subsystems, like the radio.
Figure 1: LED headlamp, energy-efficient LED headlamps can be used in an array of stylistic designs
Techniques and Technologies to Control EMI
Reducing the switching frequency of LED drivers isn’t an option; after all, the high frequency helps maintain the energy efficiency and long-lasting operation of the LEDs. Filtering the drivers can help. So can choosing LED driver ICs that are designed to minimize the effects of EMI. For example, wave-shaping circuitry that smooths the switching edges can reduce radiated EMI during pulse-width modulation (PWM) dimming. Wave-shaping circuitry is available in Maxim’s MAX16800 high-voltage, 350mA, adjustable linear HB LED driver.
Internal frequency dithering (or modulating) can also help control EMI. When you modulate the switching frequency, you can lower the peak energy and redistribute it to other frequencies and their harmonics. Spread-spectrum techniques can even move the EMI frequency to bands where the noise is not a detriment—ideal if the noise impacts sensitive parts of the circuit. Spread-spectrum techniques are also effective in helping to meet regulatory standards for EMI, as these standards generally specify maximum EMI energy at certain points in the spectrum.
Maxim’s MAX16833 family of HB LED drivers (Figure 2) improves EMI performance via frequency dithering for spread-spectrum applications. The product family also provides a level of flexibility that makes it suitable for multiple automotive lighting applications, such as high-beam/low-beam/signal lights, daytime running lights, fog lights, and adaptive front-lighting assemblies. In addition to reducing EMI noise, the LED drivers reduce harness wiring, support high-power applications with robust fault protection, and reduce system bill of materials (BOM) costs with their support for input voltages up to 65V. To learn more about Maxim’s latest HB LED driver technologies, contact your local sales rep.
Figure 2: MAX16833 simplified operating circuit