• PREMA Semiconductor GmbH

Boost LED Driver for Solar Lamps

LED solar lamps operate with automatic LED control depending on the ambient light level. The battery is charged by solar cells. Normally this requires several components like Schottky diodes, capacitors, resistors, two or three rechargeable battery cells and a photo resistor. In contrast to this standard solution the PR4403 saves several components, as it is able to drive the current for the white LED out of a single rechargeable battery cell. Also the expensive photo resistor is no longer needed.

A supply voltage of down to 0.9V is sufficient for the IC to drive a current of up to 40mA independent of the input voltage. The value of the external inductor defines the LED current. Instead of the photo resistor, the solar cell is directly connected to the IC for daylight level detection, and an optional resistor sets the light threshold. Depending on the voltage at this connection, the integrated step-up converter is switched on or off. During daytime the driver is shutdown and the solar cell charges the battery via the external Schottky diode. With decreasing ambient light the voltage at the solar cell drops, the IC is activated and drives the LED current out of the battery cell.

Deep discharge of the battery cell is prevented as the PR4403 shuts off the driver when the supply voltage drops to less than 850mV. Therefore PREMA's PR4403 saves cost for LED solar lamps as it reduces the number of components.

Applications for the PR4403 are solar garden lamps as well as house number lights, decoration lights and road markers powered by solar cells.