1～3W LED flashlight driver solution introduction

There are both boost and buck types in 1-3W flashlight LED applications. The input voltage range of boost applications is 1 to 2.5 Vdc, and the operating frequency is up to 1.2MHz; the input voltage range of buck applications is 4 to 5.5 Vdc, and the frequency is up to 1.7MHz. Both types of applications need to support 350mA or 600mA constant current output and energy efficiency higher than 90%. In 1-3 W flashlight boost LED applications, ON Semiconductor's NCP1421 boost DC/DC converter can be used. Flashlight buck LED applications in the same power range can use ON Semiconductor's NCP1529 low-voltage buck converter. The application circuit diagrams are shown in Figure 7(a) and Figure 7(b) respectively.

Figure 7: NCP1421-based boost and NCP1529-based buck 1-3W flashlight LED applications.

Linear constant current regulators especially suitable for low current LED lighting applications

The previous article discussed the requirements of LED applications in different power ranges and the suitable driving power supply solutions according to different power supply types. However, looking at different LED lighting applications, it can be found that there is a category of applications that focus on low current applications, such as commercial and industrial signage, automotive parking lights and taillights, and architectural and decorative lighting. Common driving solutions for such low current LED applications include low voltage drop linear regulators and resistors. These two driving solutions have their own advantages and disadvantages.

Fortunately, ON Semiconductor has introduced a new low-current LED drive solution, the NSI45 series of two-terminal and three-terminal linear constant current regulators (CCRs), using patent-pending self-biased transistor (SBT) technology combined with its own superior process control capabilities. This solution is simpler and lower cost than a linear regulator, but its performance is greatly improved compared to the resistor solution, filling the market gap. The NSI45 series offers many advantages, such as maintaining constant brightness over a wide voltage range, protecting LEDs from overdrive when the input voltage is high, making LEDs brighter when the input voltage is low, helping to reduce or eliminate LED coding inventory, and helping to reduce total system cost, etc., making it very suitable for low-current LED current applications.