Kaiju tech: 2015

Regulated DC Power Supply

A regulated power supply aims at providing a constant voltage regardless of the changes in the current sources. This article shows the making of a 5V constant power supply source using a Bridge Rectifier and Voltage Regulator IC. Before moving to the project let’s have a glimpse at the Bridge Rectifier and Voltage Regulators.

Bridge Rectifier is nothing but an arrangement of diodes and capacitors to convert AC into DC voltage. The diodes switch themselves on and off on the basis of polarity of alternating current, i.e. they act as a short circuit and open circuit according to the biasing that changes due to positive and negative half cycles of alternating current. This action clips some portion of the alternating voltage/current and we get some form of impure DC with curves called “Ripples” as shown in figure 2. Rectification efficiency of Bridge Rectifier is 81.2%

The following circuit, figure 1 shows a bridge rectifier without voltage regulator and filters. The simulation leads to DC with ripples as shown in figure 2.

Figure 1

Figure 2

Voltage Regulators are available in a wide range and types: Fixed output voltage, Adjustable output voltage, Switching Regulators and Special Regulators.

Here, we have used a fixed voltage regulator IC 7805 that gives an output of 5 volts. The 7800 series consist of 3 terminal positive voltage regulators with seven voltage options and can deliver currents up to 1 ampere. For further information on ICs you can consider the datasheet. http://www.ti.com/lit/ds/symlink/lm7805c.pdf

Note: If you want to make a negative power supply, than 7900 series IC can be used.

IC	Output voltage (v)	Maximum input Voltage(v)
7805	5	35
7806	6	35
7808	8	35
7812	12	35
7815	15	35
7818	18	35
7824	24	40

Capacitors used in the circuit acts as filter which bypass the ripples content through it and allows only DC to appear across the load. Figure 3 shows bridge rectifier followed by voltage regulator and capacitor filter which give pure DC without any ripples at the output as shown in figure 4

Figure 3

Figure 4

Components Required:

· 1 Step down transformer. Here used a 240- 12 v step down transformer of 1 amp. Rating.

· 4 (1N4007)diodes.

· 1 Electrolytic capacitor (1000uf).

· 2 ceramic capacitors (0.01uf).

· 1 resistance (330 ohm).

· 2 LEDs

· 7805 IC

Making the supply:

Make the design: Design can be simply made on a zero PCB or can be made on a copper clad using masking and etching process. Here, we are making it on a copper clad (you can also use zero PCB for such small circuits). The design can be made on any PCB design software, I have used PCB Express.