Application Report SLUA629A
Karthik Kadirvel and John Carpenter
Battery Charge Management
Ambient light sensors have become very common in portable electronics to adjust the brightness of the screen. These sensors automatically increase the screen brightness when a portable device, such as a cell phone, is used in sunlight and dims or turns off the display when the cell phone is placed next to the ear. In this application report, a proof-of-concept, self-powered, ambient light sensor is described which is powered by a solar cell. The solar cell is used to power the device and as a light sensor. The output of the described circuit is a square-wave pulse whose frequency is proportional to the light intensity. The circuit does not require a battery to operate and automatically starts itself when sufficient ambient light is on the sensor.
The bq25504 is an ultralow-power charger integrated circuit (IC) intended for interfacing to dc sources like solar cells, thermal harvesters, and high-impedance batteries. Its industry-leading, low-quiescent current and high charger efficiency makes it an ideal choice for charging batteries and super-capacitors from a variety of energy harvesting sources. The IC has internal circuitry to manage the voltage across the storage element and to optimize the charging of the storage element.
Download Application Report SLUA629A (187 Kb)
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Schematic of bq25504 Circuit showing LED and External Switch