Solar Sensor Draws Less Than 8 µA

Power Supply Industry News Knowledge is Power ™

Summary	Solar Sensor Draws Less Than 8 µA
Category	Other
Subcategory	Solar Sensors
Power Supply Components	" ... This design arose from a requirement for a sunrise detector with low power consumption, reliable light detection, and a real sleep mode during darkness. The sleep mode of the microcontroller with a 32-kHz clock draws about 1 mA, which was too great. The circuit described here can keep the microcontroller and following circuits completely shut down during darkness, while drawing only about 8 µA. One key challenge in creating a sunrise detector is handling the long, slow signal change from the sensor, often ramping from off to full on over tens of minutes. The use of two NAND gates in a preset RS latch configuration helps add stability and signal integrity to the sensor output. U1 is from the CMOS 4000 series in particular the HCF4011BE because these gates draw less quiescent current in static mode than the 74HC00 logic series. The circuit can be modified to detect darkness rather than daylight by using a photoresistor and modifying the circuit as shown in Figure 2. The sensitivity of the circuit is about 10 lux, which means that a single white LED light source activates the switch in darkness from 30 feet. The photosensor's resistance is 2 M in the off state and about 39 k in the on state. ... "
Webpage	More info
Author	SMPS Editor
Date	12/13/2009