Normally begin to learn about electronics power supply from the battery, for example, 9 volts, 1.5 volts, 6 volts etc. But there are disadvantage that when using battery power is discharged. I need to buy a new one. Consume more.
We should the dc power supply have a choice of AC voltage. Which it must provide a output voltage as usage often is 1.5volt, 3 volts, 4.5 volts, 6v, 9v, and the current is about 1 A.
When we view many circuit ideas, found that the as figure this below (number second the power supply projects in my life) have the best fit. We use a dc voltage regulator number LM317T is the heart of the circuit. Featured, is the constant voltage. Low noise. Almost equal to the voltage of the battery. And short-circuit protection as well.
How it works
When we push power switch (S1) on, the AC-line voltage will pass through a fuse F1 and come to transformer T1 to reduce AC volts down to 12 volts
– Then this current flow through the bridge diode model (D1-D4)-1N4001 to full wave rectifire as DC current and through C1 to filter current to smooth up and has C2 filter ripple signal before into LM317.
-LED to display power on the circuit, with R1(2K) currents to reduce it.


LM317 Linear power supply Regulator selector 1.5V,3V,4.5V,5V,6V,9V 1.5A

– The output voltage is determined by rotating a selector switch S2 a level voltage 1.5,3,4.5,5,6,9 volts respectively.
– C5 (10uF) control impedance and reduce a transient at output of IC1

– C3 (10uF)- help to reduce the ripple before is amplified when the output voltage rise up.
– C4 (0.1uF) reduce the ripple at output.
– D5 and D6(1N4001) for protects IC1 from discharging of C3 and C5 respectively. In case the input of IC1 is shorted.
The maximum output current about 1.5A depends on size of the transformer We sould choose size of 2A., Or size 1A for those who want to 1A output current only.