This is a simple and easy build photocell power supply. It uses 8 pieces of photocell and single regulator IC of MAX630. This circuit capable to deliver either 4.8 or 7.2 V regulated at 15 mA with a 3-V input from a bank of photocells. R1 should be 453K Ohm for a 7.2-V output and 274K Ohm for a 4.8-Vdc output. Regulator efficiency of this circuit is about 70%.
The Maxim’s MAX630 CMOS DC-DC regulators is designed for simple, efficient, minimum-size DC-DC converter circuits in the 5mW to 5W range. The MAX630 provide all control and power handling functions in a compact 8-pin package: a 1.31V bandgap reference, an oscillator, a voltage comparator, and a 375mA N-channel output MOSFET. A comparator is also provided for low-battery detection.
Operating current is only 70μA and is nearly independent of output switch current or duty cycle. A logic-level input shuts down the regulator to less than 1μA quiescent current. Low-current operation ensures high efficiency even in low-power battery-operated systems. The MAX630 are compatible with most battery voltages, operating from 2.0V to 16.5V.