This circuit is a small +5V power supply, which is useful when experimenting with digital electronics. Small inexpensive wall tranformers with variable output voltage are available from any electronics shop and supermarket. Those transformers are easily available, but usually their voltage regulation is very poor, which makes then not very usable for digital circuit experimenter [...]

Many discrete and ICs need bipolar (dual or ± V) supplies. This can be easily accomplished with two three-terminal regulators, as illustrated in figure. Opposite-phase ac is provided by the transformer’s secondary and a grounded center tap. The single full-wave bridge converts these into positive and negative dc voltages (with respect to the grounded center [...]

This circuit can do by begin from feed house electricity AC 220 volt 50HZ. The T1 perform modify AC Volt 220V from reduce to 30V from that time Diode D1-D4 perform rectifier to the direct current. By have R1 and R2 limit the trend and C1 perform filter voltage the electricity smoothly. It have ZD1 [...]