Voltage Regulators Circuit Diagrams

# Understanding 7805 IC Voltage Regulator

### Outline

• Introduction
• A Brief Note on 7805 Voltage Regulator
• Pin Diagram of 7805 Voltage Regulator IC
• Basic Circuit of 7805
• How to Get Constant DC Power Supply from AC?
• Circuit Diagram
• Components Required
• Working
• Important Points on 7805 Voltage Regulator IC

## Introduction

In this tutorial, we’ll explore the 7805 Voltage Regulator IC, a highly prevalent regulator IC widely employed in various applications. The significance of a regulated power supply is paramount for numerous electronic devices, primarily because the semiconductor components within these devices necessitate a constant and precise current and voltage. Any deviation from this fixed rate could potentially result in damage to the device.

While batteries serve as a crucial source of DC power, using them in sensitive electronic circuits is less ideal. Batteries inevitably deplete over time, losing their effectiveness.

Furthermore, batteries generally provide voltages such as 1.2V, 3.7V, 9V, and 12V. While these voltage levels suit circuits within that range, many TTL ICs operate on a 5V logic level. Consequently, there arises a need for a mechanism to deliver a stable 5V supply.

This is precisely where the 7805 Voltage Regulator IC comes into play. It belongs to the 78XX family of linear voltage regulators and serves as a dependable solution for generating a regulated 5V output.

## A Brief Note on 7805 Voltage Regulator

The 7805 is a three-terminal linear voltage regulator with a fixed output voltage of 5 volts that can be used in a variety of applications. Texas Instruments, ON Semiconductor, STMicroelectronics, Diodes integrated, Infineon Technologies, and others currently manufacture the 7805 Voltage Regulator IC.

They are available in several IC Packages like TO-220, SOT-223, TO-263 and TO-3. Out of these, the TO-220 Package is the most commonly used one (it is the one shown in the above image).

Some of the important features of the 7805 IC are as follows:

• It can deliver up to 1.5 A of current (with heat sink).
• Has both internal current limiting and thermal shutdown features.
• Requires very minimum external components to fully function.

## Pin Diagram of 7805 Voltage Regulator IC

As mentioned earlier, 7805 is a three terminal device with the three pins being 1. INPUT, 2. GROUND and 3. OUTPUT. The following image shows the pins on a typical 7805 IC in To-220 Package.

The pin description of the 7805 is described in the following table:

## Basic Circuit of 7805

As mentioned earlier, a regulated power supply is a device designed to function with DC voltages while consistently maintaining its output at a predefined voltage, regardless of substantial variations in the DC input voltage.

As per the datasheets for the 7805 IC, the fundamental circuitry needed for the 7805 to operate as a fully functional regulator is quite straightforward. In fact, when dealing with an unregulated DC input voltage, only two capacitors are essential for its operation (though their inclusion may not always be mandatory, depending on the specific application).

The diagram presented above illustrates all the essential components needed for the proper operation of a 7805 IC. Only when there is a considerable distance between the regulator IC and the power supply filter is a 0.22F capacitor near the input required. Similarly, the inclusion of a 0.1F capacitor at the output is discretionary, but if employed, it enhances transient response.

In this circuit, VIN represents the input voltage for the 7805 IC, which can be sourced from either a battery or an unregulated DC supply. VOUT denotes the output of the 7805 IC, providing a steady 5V regulated voltage.

## How to Get Constant DC Power Supply from AC?

While batteries can serve as a viable input source for the 7805 Voltage Regulator IC, they come with certain drawbacks, including frequent battery depletion and a gradual decline in voltage levels over time.

A superior alternative to battery usage involves employing an AC source to produce an unregulated, yet rectified DC voltage. Given that AC power sources are readily accessible in the form of mains electricity, we can design a circuit to convert AC mains power into DC and utilize it as input for the 7805 Voltage Regulator IC.

## Circuit Diagram

The following image shows the circuit diagram of producing a regulated 5V from AC Mains supply.

### Components Required

• 230V-12V Step Down Transformer
• Bridge Rectifier (or 4 PN Diodes – 1N4007)
• 1A Fuse
• 1000μF Capacitor
• 7805 Voltage Regulator IC
• 0.22μF Capacitor
• 0.1μF Capacitor
• 1N4007 Diode

## Working

This circuit accomplishes the conversion of AC power supply from the mains into an initial unregulated DC form, followed by its transformation into a stable and regulated DC output. The circuit components comprise a transformer, a bridge rectifier using diodes, a 7805 linear voltage regulator, and capacitors.

The circuit operation can be segmented into two distinct phases, as depicted. Initially, the AC mains power is converted into unregulated DC in the first phase, and subsequently, this unregulated DC is converted into a regulated 5V DC in the second phase. With this understanding, let’s delve into the operational description.

Firstly, the primary winding of a 230V to 12V step-down transformer is connected to the mains power supply. The secondary winding of the transformer is then linked.

A 1A fuse is positioned between the transformer and the bridge rectifier to limit the circuit’s current draw to 1A. The rectified DC output from the bridge rectifier is smoothed by a 1000F capacitor.

As a result, the voltage output across the 1000F capacitor is 12V DC, constituting an unregulated form. This serves as the input for the 7805 Voltage Regulator IC, which then converts it into a stable and regulated 5V DC accessible at the output terminals.

## Important Points on 7805 Voltage Regulator IC

• The first important point to note is that the input voltage should always be greater than the output voltage (atleast by 2.5V).
• The input current and output current are almost identical. This means that when a 7.5V 1A supply is given at input, the output will be 5V 1A.
• The remaining power is dissipated as heat and hence a heat sink like the one shown below must be used with 7805 IC.

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