Power controller drives high power LEDs, regulates solar cells and charges batteries

July 08, 2013 //By Luke Milner, Linear Technology Corporation
Power controller drives high power LEDs, regulates solar cells and charges batteries
The best LED drivers accurately regulate LED current for consistent color reproduction and modulate it rapidly for high contrast dimming. They also recognize and survive short and open circuits, monitor and report current levels, guard against overheating, and protect weak power supplies from excessive load currents. A standard switching converter would require a number of additional expensive amplifiers, references and passive components to fulfill these responsibilities.

In contrast, the LT3763 LED driver-controller has these functions built in—reducing BOM costs, saving board space and improving reliability. The LT3763 is more than just a high performance LED driver. Its rich feature set simplifies the design of other demanding applications, such as safe charging of a sealed lead-acid batteries, or maximum power point regulation for a solar panel, or a combination of both. The LT3763 performs these tasks with high efficiency, even at input voltages reaching 60V.

Driving LEDs

Figure 1 shows the LT3763 configured as a high power LED driver. A potentiometer at the CTRL1 pin permits manual adjustment of the regulated LED current from 0 to 20A. For thermal regulation of the LED current, a resistor with a negative temperature coefficient is mounted near the LED and connected from the CTRL2 pin to GND.

Figure 1. A single high power LED (20A) driver with analog and PWM dimming

The resistor network at the EN/UVLO pin programs the LT3763 to shut down if the input voltage falls to less than 10V. The resistor network at the FB pin defines an open-circuit condition as when the output reaches 6V, and should that ever happen, the LT3763 automatically reduces the inductor current to prevent overshoot and pulls down the /FAULT pin to mark the occasion.

The LT3763 is designed to provide flicker-free LED dimming as shown in Figure 2. This is achieved by pulling PWMOUT low whenever PWM is low and thereby disconnecting the LED, by similarly disconnecting the compensation network at VC, and resynchronizing internal switching clocks to the PWM pulse. These maneuvers ensure that subsequent pulses are identical, that the inductor current rises as fast as possible to satisfy the programmed LED current level, and that the LED light never flickers.

Figure 2. PWM dimming performance of the circuit in Figure 1

The LT3763 can be configured as in Figure 3 to deliver 350W with 98% efficiency from

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