Dual-stage LED driver solution/LED matrix solution

Car headlights, also known as front lights, are closely related to safe driving at night and in bad weather conditions. Car headlights are generally divided into halogen headlights, xenon headlights, LED headlights and laser headlights. As LED technology continues to mature, the penetration of low-end LED headlights is gradually increasing. It is expected that the penetration rate of LED headlights in China will exceed 60% in 2021.

Compared with the other three types of headlights, LED headlights have unparalleled advantages over other light sources:

• Long life: Theoretically, the life of LED can reach 100,000 hours, and the actual life can reach more than 20,000 hours. • Fast response: No delay in lighting, the response time is only tens of nanoseconds. • Reliability: Small footprint, simple structure, high shock resistance. • High efficiency: Less additional loss. Compared with the complex heat dissipation system of traditional lamps, the heat loss of LED lamps is much smaller, and the energy consumed is 80% less than that of incandescent lamps with the same luminous efficiency. The conversion efficiency can reach 85%.

Circuit Architecture

Linear drive solution

The automotive linear LED driver solution is usually used in automotive interior lighting, parking lights, and side marker lights. As shown in the figure above, the linear LED driver has no inductor, eliminating noise; the current is adjusted by the external resistor R1, and a single device can drive multiple LEDs, minimizing the number of components and simplifying the design. The linear driver solution has a simpler circuit architecture and a relatively low cost, and is suitable for lower current applications.

l Single-stage LED drive solution

The single-stage LED driver solution belongs to the switch driver solution. This driver solution is simple and cost-effective, and can be used for single front-end lighting functions such as daytime running lights, turn indicators or high/low beams. The battery voltage of the car changes greatly during cold start or load dump. In order to ensure that the LED has enough voltage to work normally, the headlight is usually configured as a boost, buck-boost, SEPIC or Cuk topology LED driver.

As shown above, the on-time begins after an off-time based on the output voltage. The on-time ends immediately after the inductor peak current threshold is reached. The device can be configured to maintain a constant peak-to-peak ripple value during the on and off times of the shunt FET dimming cycle, suitable for maintaining a linear response over the entire shunt FET dimming range.

l Dual-stage LED drive solution/LED matrix solution

The dual-stage LED driving solution belongs to the smart headlight solution. As shown in the figure below, the car headlights can use cameras to detect vehicles and objects, and then detect the environment to automatically adjust the brightness of the high/low lights, or the optimal circuit lighting status.

As shown in the circuit architecture below, the solution includes a constant voltage output booster as the front stage to create a stable DC voltage, followed by a high-bandwidth step-down constant current output LED driver to output current, and the matrix controller provides a single pixel-level LED control to achieve a fully adaptive lighting solution. Compared with the first two solutions, the dual-stage LED driver solution has a more complex circuit architecture, uses more magnetic devices, and has a higher cost, and is used in mid-to-high-end models.

Power Inductors for Automotive LED Drivers

New product release - AMWPH series of automotive power inductors

1. Product structure

2. Product Features

• Glue coating structure: This structure can effectively reduce buzzing sound, ensure product electrical properties and easily achieve product miniaturization

• Closed magnetic circuit structure: less magnetic leakage, good anti-EMI performance

• Mature technology: The product technology platform is mature, and the product is easy to realize automated production to ensure product consistency