- Voltage Regulator 7805 Definition: The 7805 voltage regulator is defined as a fixed linear regulator that provides a stable +5V DC output from an input voltage between 7V and 35V.
- PIN Configuration: The 7805 has three pins: an input pin for unregulated voltage, a ground pin for 0V, and an output pin for regulated 5V.
- Heat Dissipation: Excess energy is released as heat, requiring proper heat sinks to prevent malfunction and ensure efficiency.
- Internal Components: The internal block diagram includes an error amplifier, Zener diode, transistors, and SOA protection to stabilize and control the voltage.
- Applications: The 7805 voltage regulator is used in phone chargers, UPS systems, and other devices needing a reliable 5V power supply.
Voltage sources often fluctuate and cannot provide a fixed output. To obtain a constant and steady output, voltage regulators are used. These integrated circuits, known as voltage regulator ICs, manage voltage. This article focuses on the IC 7805.
The 7805 voltage regulator belongs to the 78xx series of voltage regulator ICs, a family of fixed linear regulators where “xx” denotes the fixed output voltage. For the 7805, that output is a +5V DC regulated supply, and the package includes provision for attaching a heat sink. The IC keeps a constant 5 V output across its whole input range, which runs up to a 35 V maximum.
PIN 1-INPUT
This pin receives the unregulated input voltage for regulation, and it must stay within 7 V to 35 V. The lower the input voltage sits above that 7 V minimum, the higher the regulator’s conversion efficiency.
PIN 2-GROUND
The ground connection attaches to this pin. It is common to both input and output (0 V).
PIN 3-OUTPUT
The regulated output is taken from this pin. Its value is 
Heat Dissipation in IC 7805
In the 7805 voltage regulator, much energy leaves as heat. The heat comes from the difference between the input and output voltages: the larger that difference, the more heat is produced. Without a proper heat sink, the excess heat can cause malfunction.
The minimum difference between input and output voltage needed to keep the output in regulation is called the dropout voltage. Keeping the input only 2 to 3 V above the output limits the wasted energy, and a suitably sized heat sink should dissipate whatever heat remains.
We can now analyse how generated heat varies with the input voltage through two examples.
Assume a system with an input voltage of 16 V and a required output current of 0.5 A.
The heat generated is
So 5.5 W of heat is wasted while the delivered power is only
More than twice the delivered energy is lost as heat.
Next consider a lower input of 9 V.
In this case, the heat generated is 
The conclusion follows: at high input voltage this regulator IC becomes highly inefficient. If you’d like to learn more, we offer a large range of free digital electronics MCQ questions.
Internal Block Diagram of 7805 Voltage Regulator
The internal block diagram of IC 7805 is represented in the figure below:
The block diagram comprises an error amplifier, a series pass element, a current generator, a reference voltage, a starting circuit, SOA protection and thermal protection.
The operational amplifier functions as the error amplifier, while the Zener diode provides the reference voltage.
A Transistor serves as the series pass element: it dissipates surplus energy as heat and holds the output steady by controlling the current between input and output. SOA stands for Safe Operating Area, the combination of voltage and current within which the device works without self-damage. For SOA protection, a bipolar transistor is implemented together with a series resistor and an auxiliary transistor. A heat sink provides thermal protection when the supply voltage runs high.
Regulated Power Supply Circuit
The voltage regulator 7805 and the other components are arranged in the circuit as shown in figure.
The purposes of the components coupled to the IC 7805 are explained below.
C1: a bypass capacitor that diverts very small spikes to earth.
C2 and C3: these are the filter capacitors. C2 smooths slow changes in the input voltage reaching the circuit, while C3 smooths slow changes in the regulator’s output. Larger values give stronger smoothing, but these capacitors alone cannot remove very small fluctuations in the input and output voltages.
C4: like C1, this bypass capacitor diverts very small spikes to ground or earth without influencing other components.
Applications of Voltage Regulator 7805 IC
- Current regulator
- Regulated dual supply
- Building circuits such as phone chargers, UPS power supplies and portable CD players
- Fixed output regulator
- Adjustable output regulator etc.
