• 
  This project is based on another design we found on the internet, with a few modifications that we explain below. In this guide, we show step by step how to build a regulated power supply with six commonly used output voltages: 3.3V, 5V, 6V, 9V, 12V, and 15V. The maximum current is 1A. The power supply also provides a non-regulated 30V output. The complete circuit is shown in the figure below. At the input, a transformer converts the 220V AC mains voltage to 24V AC. Voltage conversion from AC to DC is done using a rectifier with four MR-type diodes. A 2200µF, 50V capacitor at the rectifier output acts as a filter, reducing ripple voltage and providing approximately 30V to the LM317-220 voltage regulator.

• The LM317 output voltage depends on the resistor connected from its adjustment pin to ground. The datasheet provides the following relationship:

• We start by considering Vref as the nominal reference voltage between the output and adjustment terminals. The output voltage can be calculated using the standard voltage divider equation:

 

The datasheet specifies Vref = 1.25V.

This reference voltage appears across resistor R1, producing a constant current I through the output-setting resistor R2, giving the output voltage:

Using this equation, we calculate R2 for different output voltages. For R1, we use 220 Ohms to limit the LM317 output current.

For example, to calculate R2 for a 3.3V output:

The same procedure is used for the other voltages: 5V, 6V, 9V, 12V, 15V.

If the calculated resistor is not commercially available, two resistors in series can be used:

(Two resistors: 560 Ohms + 270 Ohms)

(Two resistors: 680 Ohms)

(Two resistors: 390 Ohms + 1.5kOhms)

(Two resistors: 1.2kOhms)

Protection components: D5 (diode between input and output) protects the LM317 from capacitor discharge in case of a short circuit. D6 protects against output short circuits. Transistor + red LED triggers if current exceeds 1A, alerting the user.

Component List:

1x Transformer (EI 66/23 124)

4x Diode (MR826)

2x Diode (1N4007)

2x LEDs (green and red)

3x Resistors (1.5kOhms)

1x Resistor (220Ohms)

2x Resistors (330Ohms)

4x Resistors (1.2kOhms)

1x Resistor (360Ohms)

1x Resistor (1kOhms)

1x Resistor (270Ohms)

1x Resistor (560Ohms)

2x Resistors (680Ohms)

1x Resistor (390Ohms)

2x Diode (1N4007)

1x LM317

2x Ceramic capacitors 100nF

1x Electrolytic capacitor 2200uF

2x Electrolytic capacitors 470uF

Pictures:

Downloads:

Documentation
Documentation and component list
Simulation
Multisim simulation file
LTSpice simulation file