LM7805 is a voltage regulator IC that maintains a 5 v constant output voltage. This voltage regulator is a member of the 78xx series of constant linear voltage regulators.
LM7805 is a popular low-cost voltage regulator IC used to maintain voltage fluctuations with a wide range of applications.
- Why do we need a Voltage Regulator?
- What is LM7805 voltage regulator?
- Features of the LM7805 voltage regulator
- What is LM in LM7805?
Why do we need a Voltage Regulator?
When voltage fluctuation happens in a circuit, at that time a constant output cannot be obtained from the input voltage source. To eliminate this, a system is required to maintain a fixed voltage supply automatically. Such systems are known as Voltage Regulator.
These voltage regulators are commonly used for stabilizing the DC voltages in computer power supplies. Also, in automobile alternators and power station generation, they are used in controlling the output.
What is LM7805 voltage regulator?
LM7805 is a three-pin IC voltage regulator where:
- Input pin is used for receiving the fluctuating DC voltage.
- Ground pin is used for establishing ground or common.
- Output pin supplies a constant 5 volts DC output.
LM7805 Voltage Regulator is currently manufactured by Infineon, Diodes incorporated, STMicroelectronics, ON Semiconductor, Texas Instruments, etc.
Features of the LM7805 voltage regulator
These are the following features of the LM7805 voltage regulator:
- Thermal shutdown
- Internal current limiting
- It can deliver a current up to 1.5 A with a heat sink.
- It can operate efficiently with minimum external components.
LM7805 is available in several IC Packages like TO-220, SOT-223, TO-3, and TO-92. TO-220 is a commonly used package out of these IC packages.
Due to the following features, it is commonly used in electronic circuits as a regulated power supply.
What is LM in LM7805?
A prefix is given by the manufacturer to identify the version. The prefix LM stands for linear monolithic. LM series was firstly manufactured by National Semiconductor & the first time prefix LM was given for linear ICs.
What does 7805 stand for?
7805 in LM7805 signifies two meanings-
- “78” means that it is a positive voltage regulator. It produces a voltage that has a positive magnitude with respect to the ground.
- “05” represents its output voltage value.
Hence, LM7805 IC provides +5 volts regulated power supply.
The table below gives the description of the pins:
|I/P||Input||Fluctuating input voltage is applied at this pin.|
|G||Ground||This is the Ground or common point of the circuit.|
|O/P||Output||5V regulated output pin.|
Let us discuss each pin in a bit more detail:
- It is an Input pin.
- An unregulated voltage is applied to this input pin for regulation.
- The voltage range must be applied between 7V-35V.
- Its maximum efficiency is achieved at 7.2V input.
- It is a Ground pin.
- It is used to establish the ground which is common to both input and output.
- It is an Output pin.
- The regulated output is taken from this output pin.
- The output voltage is +5V.
Specifications of the LM7805
The specifications of the LM7805 voltage regulator are listed in the table below:
|Maximum input voltage||25V|
|Minimum input voltage||7V|
|Output voltage (regulated)||5V|
|Junction temperature (in degree Celsius)||0-125|
|Package||KTE and TO-220|
|Protection||Short circuit and thermal overload|
How to use LM7805 as a Voltage Regulator?
To use the LM7805 as a voltage regulator, two capacitors are connected across the input and the output pin. Connect the Input pin of the IC to the fluctuating voltage that needs to be regulated. The middle terminal should be Grounded. The remaining terminal then gives a stable 5V output.
5V Power supply using LM7805(220v – 5v)
This circuit converts 220V AC voltage to a stable 5V DC output. Let’s see how the circuit works.
To understand the working, we can divide this circuit into two parts. In the first part, AC power is converted into DC power while in the second part, this DC power is changed into a regulated 5V DC.
First part: Converting AC to DC
The circuit consists of a step-down transformer whose primary winding is connected to the AC supply. It converts the AC supply voltage from 230V to 9V. The secondary winding of the transformer is connected to a bridge rectifier.
The bridge rectifier converts the AC voltage to DC voltage with the help of a 1000μF capacitor. Thus, an unregulated 9V DC is obtained at the output.
It must be observed that a 1A fuse is present between the transformer and the bridge rectifier. This fuse limits the current to 1A. If somehow the current exceeds this value, the fuse gets burned, thus protecting the external load and other ICs.
Second part: Obtaining regulated output
Now the DC power obtained above works as an input to the 7805 voltage regulator IC. After this regulator, regulated 5V DC is obtained as output at its output terminals.
Note: While using this circuit, keep in mind that in order to create a proper power flow from the input to the output of LM7805, the input voltage value must be greater than the output voltage value. For example, when 7.5V-1A is applied at the input, the output obtained will be 5V-1A.
Heat Dissipation in LM7805
In IC 7805 voltage regulator, the exhaust energy is released in the form of heat which is equal to the difference in input and output voltage. So, there can be two cases:
Case 1: If the voltage difference between the input and output voltage is less, the heat generation will be less.
Case 2: If the voltage difference between the input and output voltage is more, the heat generation will also be more.
This excess heat may damage the IC. Thus, a heat sink must be always used with the IC to absorb the heat.
Equivalents of LM7805
The following voltage regulators can be used to replace LM7805:
- L78M05(0.5 A)
LM7805 Package types
LM7805 is available in the market in the following packages:
- TO- 220
TO-220 is a commonly used package out of these IC packages.
LM7805 applications are as follows:
- Current regulator
- Fixed Output regulator
- Reverse bias protection circuit
- Positive regulator
- Regulated Dual-Supply
- Output Polarity-Reverse-Protection Circuits
- Adjustable Output regulator
To download the datasheet of LM7805, click here.