When there are fluctuations in the circuit, then the fixed output cannot be given by all voltage sources. To deal with this, a system is designed to maintain a constant voltage level automatically is Voltage Regulator. These voltage regulators are used in computer power supplies for stabilizing the DC voltages. Coming to power station generation plants and automobile alternators, the output is controlled by these voltage regulators. The regulation of one or more AC or DC voltages is done depending on the design of the voltage regulator. This article discusses the IC 7805 Voltage Regulator and its working.
What is the 7805 Voltage Regulator?
Definition: Voltage regulator like IC7805 belongs to the 78xx series ICs. In the 78xx series, xx represents the fixed output voltage value and 7805 is a fixed linear voltage regulator. Batteries provide a voltage of 1.2V, 3.7V, 9V, and 12V. This voltage is good for the circuits which voltage requirements are in that range. The regulated power supply in this regulator is +5V DC.
The 7805 voltage regulator is a three-terminal voltage regulator IC. In various applications, a 7805 voltage regulator with a fixed output voltage is used. The availability of this is through various packages like SOT-223, TO-263, TO-220, and TO-3. Among this, TO-220 is the most used one. There are many important features in the 7805 IC.
Minimum external components are enough for functioning
- 1.5 A of current can be delivered in this 7805 IC
- It has internal current limiting features
- It also consists of thermal shutdown features.
Pin Diagram
Here is the pin diagram of 7805 voltage regulator IC and its description are discussed below.
7805 Voltage Regulator
Pin1: Input
This is an input pin and the voltage range should be between 7V to 35V. an unregulated voltage is applied to this input pin for regulation. The pin will receive its maximum efficiency at 7.2V input
Pin2: Ground
Pin2 is the ground pin, it means the ground is connected to this pin. Input and output are common to it.
Pin3: Output
Pin3 is the output pin, where the regulated output is taken by this pin. It is about 5V(4.8V to 5.2V)
Here Energy is exhausted in the form of heat In IC 7805 voltage regulator. The heat released is the input and output voltage difference. If the difference is less in between input voltage and output voltage, the heat generation will be low and if the difference between the input and output voltages are high, the more heat is generated. due to this heat malfunction occurs even without a heat sink.
7805 Voltage Regulator Circuit
Here is the circuit of the 7805 voltage regulator. The basic circuit of 7805 is very simple. It just needs two capacitors if the input is unregulated DC voltage, even the two capacitors used are also not mandatory. This 7805 circuit is capable of upholding fixed output voltage even if some changes take place in input voltage.
7805 Circuit
When the distance between the power supply filter and the regulator is high, then the 0.33uF capacitor is needed to place it near the input. The 0.1uF capacitor placed is not a mandatory one, its optional, it is used for the transient response.
Vin is the input voltage, here it is shown as the source from battery. 7805IC receives input from the battery of an unregulated DC. Vout is the output voltage. the output is received from the 7805 IC. the output received there is the regulated 5V.
7805 Voltage Regulator Working
This is the circuit diagram of producing a regulated output of 5V from the AC mains supply. This circuit uses the following components.
7805 Voltage Regulator Circuit Working
- 230V – 12V step down transformer
- 1A fuse
- 7805 voltage regulator IC
- Capacitors
- IN4007 diode
- Bridge rectifier
When AC power supply is given from mains, first it is converted into unregulated DC, and finally, constant regulated DC can be generated like the output from this circuit. Mainly the circuit is designed with a bridge rectifier which is made up of diodes, transformer, capacitors, and linear 7805 voltage regulator.
It takes place in two steps, on the first step AC power supply is converted into unregulated DC and in the second step, this unregulated DC is converted into regulated DC. We will see the process now.
The primary step down transformer is connected to the mains supply. The secondary of a step-down transformer is connected with a bridge rectifier, here it is a combination of 4IN 4001 diodes.
In between the bridge rectifier and the transformer, a 1A fuse is placed. It is used for current limitation i.e to limit current to 1A drawn the circuit. the rectified DC which is given by the bridge rectifier is smoothened by the capacitor. So the output is unregulated DC about 12 V DC. Then the voltage regulator IC receives this unregulated Dc as input and this regulator converts the unregulated DC to regulated DC about 5V and finally, output terminals receive this regulated DC.
Heat Dissipation in IC 7805
As we have seen previously, in the form of heat a lot of energy will get exhausted. This heat will be generated due to the difference between the input voltage and the output voltage. The high amount of will is generated if the difference is high. This heat will result in malfunctioning. So to avoid this malfunction, a heat sink is used.
Scaling the Output
Bandgap circuit receives an input signal like Vin from the 7805 scaled output and this provides an output of error signal. The traditional bandgap reference will have the feedback loop and that loop is removed by this bandgap circuit, this entire will chip becomes a feedback loop.
If 5V output voltage which is correct is produced then voltage divider gives 3.75 at Vin. Even a small change in Vout propagates through Q6 and R7 providing voltage at Q7 base for rising or falling accordingly. Then Q7 and Q8 amplifies the changes and gives error signals. This error output increases or decreases the current through the output transistor. the output voltage will get adjusted by a negative feedback loop until its current.
Applications
The 7805 voltage regulator applications include the following.
- Regulated dual supply
- Current regulator
- Fixed output regulator
- Reverse bias projection circuit
- Adjustable DC voltage regulator etc
- This 7805 IC is used in building circuits for a phone charger, infrared remote control extension, UPS power supply, and even portable CD player
Please refer to this link to know more about LDO Regulator & Voltage Regulators
Thus, this is all about an overview of IC 7805 voltage regulator, pin configuration, circuit diagram with working, and its applications. Here is a question for you, what are the different types of voltage regulators?