One Cell Switching Regulators

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Here are two switching regulators that will run off one alkaline or nicad/nimh cell and produce 5 volts.

Operation is from .8 to 1.6 volt. Below 1 volt less current is available.

The first circuit uses "PFM" (pulse frequency modulation) and is good for 3 to 5 milliamps output, which should be enough for a PIC microcontroller and an LCD display. With no load the circuit draws about 750 microamperes.

The second circuit uses PWM and is good for at least 50 milliamps. However since it is PWM it draws 40 milliamps even when there is no load.

The PFM circuit is a little fussy about zener diode leakage.
If you substitute a different inductor value, substitute higher inductance if you have the choice. Low resistance inductors give the best efficiency.

PFM Circuit

Download schematic PDF

PWM Circuit

Download schematic PDF

Bob Blick, July 5, 2003