Abstract: The simple circuit discussed in this article is capable of regulating the drive current of high-brightness LEDs . The circuit uses a non-custom, highly integrated step-down switching regulator (MAX5035) to accurately control the current flowing through the LEDs. The MAX5035 DC/DC converter maintains a fixed 125kHz operating frequency over a wide input voltage range of 7.5V to 76V, making it ideal for automotive applications. Brightness control can be achieved by analog (linear adjustment) or low frequency duty cycle (PWM adjustment).
　　 High-brightness LED development background
In recent years, high-brightness LEDs (HB LEDs) have become increasingly popular as light sources in various lighting systems because of the high reliability of high-brightness LEDs, which can last for tens or even tens of thousands of hours, compared to traditional incandescent The life of a lamp or halogen lamp is several orders of magnitude higher. Based on this advantage, high-brightness LEDs are commonly used in automotive lighting, public signage and signal signage, and architectural lighting.
High-brightness LEDs are specially processed PN junction semiconductor devices that emit white, red, green, or blue light (and possibly other colors of light) when forward biased. As PN junctions they exhibit VI characteristics similar to conventional diodes but have a higher junction voltage drop. With the forward voltage reaching VF (from 2.5V for red LEDs to 4.5V for blue LEDs), the current flowing through the LEDs is small; once the forward voltage reaches VF, the current will rise rapidly (same as a conventional diode). Therefore, current limiting measures must be used to limit the rise of current to prevent LED damage. There are currently three basic current limiting methods. Table 1 compares these three methods:
Table 1 Comparison of current limiting methods
Assume a white LED: VF = 4V, ILED = 350mA, VIN = 12V.
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