LED Automotive Headlight Power Systems: An In-Depth Analysis

LED automotive headlights are revolutionizing our night-time driving experiences. With their enhanced energy efficiency, longevity, and visibility, they’re fast becoming a preferred choice among drivers. This blog post offers an in-depth exploration of LED headlight power systems, discussing their components, temperature management, and the impacts of power surges and fluctuations. Whether you’re an automotive enthusiast or simply curious about lighting technology, this post caters to you.

The power system is the core of LED automotive headlights, tasked with regulating and delivering power to the LEDs. Broadly, it can be bifurcated into two types: constant current power supplies and linear constant current power supplies.

Buck structure

Synchronous buck structure

These are the most commonly used power supplies, subdivided into the stable and cost-effective classic buck structure and the more efficient yet expensive high-efficiency synchronous buck structure.Depending on the power supply installation, we have two categories:

Built-in Power Supply

Here, the power supply integrates with the lamp body, facilitating a compact size and stylish appearance. However, due to spatial constraints, the lamp’s power output is somewhat limited.

External Power Supply

In this configuration, the power supply is distinct from the lamp body, promoting superior heat management and supporting high-power applications. This design is more prevalent due to its practical benefits.

This newer power supply variant typically employs a small package chip with built-in MOS and current control. It achieves constant current control with minimal external resistors and capacitors. Common specifications range from 1A to 3 A. Despite being smaller, this power supply generally yields lower efficiency and generates more heat. Consequently, it’s often positioned at the other end of the copper plate hosting the lamp bead to facilitate heat dissipation. This power supply is an ideal fit for cost-sensitive LED headlights.

LED automotive headlights, with their high power density, primarily rely on fans for cooling. Effective temperature management is therefore critical. All power supply chips for LED automotive headlights feature temperature management capabilities:

• Power Supply Thermal Management: Power supplies are shrinking to cater to aesthetic preferences and miniaturization requirements, posing a challenge to thermal management. A common strategy involves incorporating a temperature control function in the power supply control chip. This reduces power output when the chip’s internal temperature reaches around 110°C – 140°C, thereby controlling the heat.

• LED Lamp Body Heat Management: To prevent potential risks associated with fan failure or cooling system issues, managing the lamp body temperature is vital. Typically, an NTC resistor is built into the lamp body, and the power supply output decreases as the lamp body temperature rises, ensuring stability. (For a more detailed understanding of LED automotive headlamp thermal management systems, please read our previous blog, “An In-Depth Exploration of LED Automotive Headlight Temperature Control Systems”)

In addition to high-temperature protection mechanisms, the power supply is also safeguarded against reverse supply polarity—a common error. A BUCK circuit-based structure with reversed supply polarity could cause a short circuit, damaging the power supply and even posing other dangers.

Schott diodes or MOSFETs are often added at the power supply input to prevent hazards associated with reverse power polarity. Diodes are cheaper but have a large voltage drop, leading to significant losses and heat in high-current applications. In contrast, MOSFETs, although more expensive, are a preferable choice.

LED headlights typically draw power from the vehicle’s battery, minimizing the effects of power surges. However, voltage fluctuations during engine startup and acceleration deserve attention.To adapt to the 12V power supply system of most vehicles and the current popular step-down structure power supply characteristics, most LED headlights use 9V (and a few 6V) LED chips. This reduces the voltage difference between the two ends of the power supply, allowing for higher efficiency. There are however a few manufacturers who opt to use 12V LED beads. However, there are some manufacturers that prefer to use 12V LED chips because the battery voltage after starting the car is usually around 13.2V, but it may not be the best choice for general applications.

For vehicles with a 24V power system, the power supply efficiency decreases, leading to increased heat generation. The ideal solution would be to use higher voltage-rated LED beads (e.g., 21V) to accommodate the 24V power system. However, no manufacturer seems to have adopted this approach yet.

To ensure the longevity of your LED headlights:

• Keep the power supply away from heat-generating objects.

• Allow the power supply a few minutes to cool after extended use before touching it.

• Due to size limitations, power supplies usually do not have an internal fuse. Installation should be done to ensure that the supply wire passes through a fuse, this is not usually a problem as the car’s original socket usually passes through a fuse, but be careful if any modifications are made to the wiring.

With ongoing advancements in electronic components, we can anticipate future power supplies becoming increasingly efficient. Moreover, catering to individual user needs will lead to a greater variety of intelligent LED headlights in the market.

Understanding the power system of LED headlights, the importance of temperature management, and the impact of power surges and fluctuations is crucial to optimizing their performance and lifespan. As technology continues to evolve, LED headlights will persist in improving, providing safer and more efficient lighting solutions for our vehicles.