fixed voltage regulator

C1 filters the noise and spikes off the ac. Adjust the circuit for 9 V output voltage with the P1 potentiometer. Link

This design was generated as part of a remote weather station project. One of the requirements of the design is that it have a solar-powered supply with rechargeable batteries. This design is based on a photovoltaic array available from Radio Shack called a BatterySAVER (part number 980-1045). It was designed to charge your car battery [...]

The 15v zener is fed via the 4K7 resistor from the input. With 0.6v across the base - emitter of the PNP transistor, this establishes a voltage of 14.4 across the 3K3, so there must be a current of nearly 4.4mA through the 3K3. This current is available to feed the emitter of the transistor [...]