This simple circuit, consisting of two LEDs and a photo diode, generates a negative voltage with a current level of a couple milliamps. It is ideal for supplying a negative rail to low power “rail to rail” op amp circuits.source

Sometimes you need a simple negative power supply. The best example is the contrast PSU for common small LCD device. Building -5V from a battery or a wallmart supply isn’t really easy.Here is a simple circuit that is able to provide -5V, -12V, -15V. The circuit used the MAX 764/765/766 series. You can simply change the chip to provide the good output.

The MAX764/MAX765/MAX766 inverting switching regulators are highly efficient over a wide range of load currents, delivering up to 1.5W. A unique, current-limited, pulse-frequency-modulated (PFM) control scheme combines the benefits of traditional PFM converters with the benefits of pulse-width-modulated (PWM) converters.

source