Design of a Power Supply DC Variable from 1.2 to 32 volts

Hello friends of Steemit, I want to share with you how to build a source that supplies variable DC voltage between 1.2 to 32 volts, controlled through a potentiometer. The maximum current value at the output is approximately 1 amp.

The schematic diagram of the circuit used is shown in Figure 1. This circuit offers multiple advantages, the possibility of adjusting the output to a DC voltage determined according to the requirements, allowing its applications to be greater. If it is required to vary for example the speed of rotation of an engine, this type of circuit would be the one indicated for that purpose. It can also be used in research or teaching projects.

Figure 1 - Schematic diagram of the circuit

Materials:

Resistances:

1 2,4 KΩ a 1/4W (R1)
1 220Ω a 1/4W (R2)
1 Potentiometer of 5K (P1)

Capacitors:

2 2200μF/50V electrolytics (C1, C2)
1 10μF/50V electrolytic (C3)
1 1μF/35V Tantalum (C4)

Semiconductors:

1 LM317 voltage regulator (IC1)
1 green 5 mm LED (D5)
2 Diode 1N4004 (D6, D7)

Various:

1 Transformer (T1)
Primary 110 or 220VAC
Secondary 24VAC / 1A

Measuring equipment

Oscilloscope
Multimeter

Figure 2 - Materials Used

In the first phase a reducing transformer was used, which converts the voltage 110VAC to 24VAC. It is important to remember that the voltage at the output of the reduction transformer remains alternating (Figure 3).

Figure 3 - Visualization of the voltage at the rectifier bridge output without filtering capacitors.

This alternating voltage at the output of the reduction transformer is then rectified with a BR-84D (bridge rectifier).

Figure 4 - Rectifier Bridge BR84D
Source

If you do not have this BR-84D rectifier, you can use the diode configuration shown in the following diagram.

Figure 5 - Configuration of Diodes
Source

Subsequently, the filtering process is necessary to obtain a direct current voltage. This filtering stage is achieved in capacitors C1 and C2. (Figure 6).

Figure 6 - Visualization of the DC voltage at the output of the filtering capacitors C1 and C2

The suggested values for capacitors C1 and C2 are 2200μF each. LED D5 is a voltage indicator at that point. Since this voltage at the output of the capacitors is not regulated, an LM317 is used to regulate and stabilize this voltage.

The LM317 is an integrated circuit that can adjust the voltage according to the needs you have. For its correct operation it must operate with resistors, capacitors and diodes. These elements (P1, D6, D7, R2) are what allow the LM317 to be adjusted to obtain the output voltage (Figure 7).

Figure 7 - LM317
Source

The potentiometer P1 of 5KΩ allows to adjust the output voltage to the desired value. The diodes D6 and D7 protect against peaks of reverse voltage to the regulator.

Figure 8 – Regulator with Protection Diodes
Source

The equation shown in Figure 8 allows obtaining the desired output voltage value, where the adjustment current (I_ADJ) has a typical value for LM317 100μA.

The following pictures shows the minimum voltage and the maximum voltage of the variable voltage source controlled through the potentiometer (Figures 9 and 10).

Figure 9 - Display of the minimum voltage of the DC source

Figure 10 - Display of the maximum voltage of the DC source

References:

Electronica-Digital-Cekit-34-Proyectos-practicos-para-construir
ROBERT L. BOYLESTAD, LOUIS NASHELSKY. Electronic Devices and Circuit Theory EDITORIAL PEARSON
http://www.alldatasheet.com/view.jsp?Searchword=LM317T&sField=4

I hope that this publication has given you knowledge about the subject. If you have any questions, please leave your comment and then I will gladly try to clarify them.

Thanks for reading my publication.

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wilians (52) · 7 years ago

Excellent post @lorenzor, very useful this type of voltage source for research work. Very interesting the use of the BR-84D rectifier replacing the rectifier diodes Thank you for sharing this information.

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lorenzor (59) · 7 years ago

Thanks for reading and commenting @wilians. Yes, it is actually more practical to build a variable voltage regulator with the use of the BR-84D. There are designs that use rectifier diodes, everything depends on the available components.

cheetah (77) · 7 years ago

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