Power controller drives high power LEDs, regulates solar cells and charges batteries: Page 4 of 5

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.
requirements of any solar panel.

Figure 6. 70W solar energy harvester with maximum power point regulation. For full resolution click here.

In the configuration shown in Figure 6, the converter can generate whatever inductor current, up to 5A, is required to hold the panel voltage at 37V. Input voltage feedback is via the voltage divider at the FBIN pin, which in turn regulates the inductor current to what is actually necessary to hold the panel at peak power in any given light condition.

As shown in Figure 7, the process of charging a battery with a solar panel looks very similar to charging with a low impedance supply as before. The difference is that the regulated inductor current (charge current) is not preset by the designer, but is instead adjusted on the fly via the feedback loop regulating input voltage. This effectively minimizes charge time, since input power is maximized at all times, regardless of panel illumination.

Figure 7. Solar powered SLA battery charging

Since the LT3763 has the capability of regulating input voltage and current, as well as output voltage and current, and provides a fault flag with C/10, it can easily be used with a wide variety of solar panels to charge many different types of batteries.

Monitoring Current Levels

In each of the applications presented here, the LT3763 provides an additional service by monitoring the input and output current levels. Voltages across the IVINP and IVINN pins ranging from 0 to 50mV are amplified with a gain of 20, and the resulting voltage appears at the IVINMON pin. The voltage at the ISMON pin is an identical amplification of the voltage across the SENSE+ and SENSE– pins, as shown in Figure 8.

Figure 8. Current monitor outputs in an LED driver application with PWM dimming

These signals are helpful in systems that must verify the current provided to LEDs or measure the efficiency of voltage conversion. They

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