enough regulation for low current requirements. The transformer steps down the AC mains voltage to 15 volts and 1N4401 diodes bridge rectifies these voltages. A 250uF capacitor is used for filtering and 150 ohms resistors are used for limiting the current. The two 12 volt 1 watt zener diodes are used to perform the voltage regulation task.
The figure below shows a circuit diagram of a simple 12V dual power supply using zener diodes. A dual power supply circuit can be very useful to operate many electronic projects; there fore it is essential to have one on your electronics workbench.