Buck Converter Powers 5-V Circuits From 12-V Solar-Cell Array

摘要

D2 provides a 2.5-V dc reference voltage at U2a pin 3. R4 and R5 form a divide-by-2 voltage divider, resulting in a voltage near 2.5 V dc at U2a pin 2 when the output voltage is 5 V dc. If the voltage at U2 pin 2 is greater than 2.5 V dc (that is, the output voltage is greater than 5 V dc), the oscillator is disabled, which results in a very small amount of current drawn from the solar cells. If the SMPS output is less than 5 V dc, the oscillator turns on and charges the filter capacitors.