- 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 lesson, we’ll look at the 7805 Voltage Regulator IC, which is one of the most widely used regulator ICs. A Regulated power supply is critical for many electronic devices since the semiconductor materials used in them have a constant rate of current and voltage. If there is any departure from the fixed rate, the gadget may be damaged.
Batteries are one of the most important sources of DC power. Using batteries in sensitive electronic circuits, on the other hand, is not a good idea because batteries ultimately deplete and lose their capability.
Also, the voltage provided by batteries are typically 1.2V, 3.7V, 9V and 12V. This is good for circuits whose voltage requirements are in that range. But, most of the TTL IC’s work on 5V logic and hence we need a mechanism to provide a consistent 5V Supply.
Here comes the 7805 Voltage Regulator IC to the rescue. It is an IC in the 78XX family of linear voltage regulators that produce a regulated 5V as 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:
| PIN NO. | PIN | DESCRIPTION |
|---|---|---|
| 1 | INPUT | Pin 1 is the INPUT Pin. A positive unregulated voltage is given as input to this pin. |
| 2 | GROUND | Pin 2 is the GROUND Pin. It is common to both Input and Output. |
| 3 | OUTPUT | Pin 3 is the OUTPUT Pin. The output regulated 5V is taken at this pin of the IC. |
Basic Circuit of 7805
As I previously stated, a regulated power supply is a device that operates on DC voltages and can maintain its output correctly at a set voltage at all times, even if the DC input voltage varies significantly.
According to the 7805 IC datasheets, the basic circuit required for the 7805 to function as a complete regulator is fairly simple. In fact, if the input supply is an unregulated DC voltage, just two capacitors are required (even those are not mandatory depending on the implementation).
The circuit above depicts all of the components required for a 7805 IC to function properly. Only if the distance between the regulator IC and the power supply filter is large is a 0.22F capacitor near the input necessary. The 0.1F capacitor at the output is also optional, but if utilised, it improves the transient responsiveness.
In this circuit, VIN is the 7805 IC’s input voltage, and the source might be a battery or an unregulated DC. VOUT is the 7805 IC’s output, which is a Regulated 5V.
How to Get Constant DC Power Supply from AC?
Although batteries can be utilised as an input to the 7805 Voltage Regulator IC, there are several drawbacks, such as frequent battery discharge and a decline in battery voltage levels with time.
The greatest alternative to using batteries is to use an AC source to generate an unregulated but rectified DC voltage. We may create a circuit to convert AC Mains to DC and provide it as an input to the 7805 Voltage Regulator IC because AC Source is readily available as a mains source.
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
With the help of this circuit, the AC power supply from the mains is first converted into an unregulated DC and subsequently into a constant regulated DC. The circuit consists of a transformer, a diode-based bridge rectifier, a 7805 linear voltage regulator, and capacitors.
The circuit’s operation can be divided into two halves, as you can see. The AC mains is converted to unregulated DC in the first portion, and then this unregulated DC is transformed to regulated 5V DC in the second section. So, with this in mind, let us begin describing the working.
The primary of a 230V to 12V Step down transformer is connected to the mains supply at first. The transformer’s secondary is connected.
Between the transformer and the bridge rectifier, a 1A fuse is installed. This will keep the circuit’s current draw to 1A. With the help of a 1000F capacitor, the rectified DC from the bridge rectifier is smoothed down.
As a result, the output across the 1000F Capacitor is 12V DC, which is unregulated. The 7805 Voltage Regulator IC receives this as an input. The 7805 IC then transforms this to a regulated 5V DC, which the output terminals can access.
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.
