Voltage Regulator
A fixed or linear voltage regulator is a device or circuit which is responsible for providing a constant dc output voltage for any changes in input voltage or load conditions. It is the most essential part of electronic devices. It acts as a buffer for protecting the components of the circuit from damage. It can regulate both ac and dc voltages depending upon its design.
There are mainly two types of voltage regulators. They are
- Linear voltage regulator
- Switching voltage regulator
Both types of voltage regulators regulate the voltage of the system but the linear voltage regulator operates with low efficiency than the switching voltage regulator.
There are mainly three components that consist in voltage regulators. They are: Feedback circuit, Stable Reference Voltage, and Pass element Control Circuit.
Here, we are going to discuss in detail about Linear Voltage Regulator.
Linear Voltage Regulator
A linear voltage regulator is a regulator device that is used to maintain the specified output voltage that remains constant despite variations in input voltage and load condition. It uses an active pass device (such as BJT or MOSFET) which is controlled by a high gain amplifier. The variable conductivity of the active pass element is accountable to maintain the output voltage. The performance of a linear voltage regulator is to act as a voltage divider to generate the regulated output voltage.
In a linear voltage regulator, a linear component (such as resistive load) is used to regulate the output voltage. The transistor stays in an active region or ohmic region or linear region of its operation during the voltage regulation.
In order to maintain a constant output voltage, the internal resistance can be varied. The variable resistance is provided by using a transistor which is controlled by the amplifier feedback loop.
A linear voltage regulator is also called a step-down converter where the output voltage is always less than the input voltage. It consumes some of the power and converts it into heat in order to generate a constant output voltage.
Linear voltage regulators normally consist of three pins: the Input pin, Output pin, and Ground pin. The pin-out diagram for LM 7805 voltage regulator is shown in the figure below.
Types of Linear Voltage Regulator
Based on the connection of load, there are mainly two types of Linear Voltage Regulators. They are:
- Series Voltage Regulator
- Shunt Voltage Regulator
Series Voltage Regulator
In a series voltage regulator, a variable element or active pass element such as a transistor is connected in series with the connected load. The constant output voltage across the load is achieved by varying the resistance of the series element with respect to the load.
Series voltage regulator is the more common form of the voltage regulator. It is more efficient than a shunt voltage regulator.
The circuit diagram for a typical series voltage regulator is shown in the figure below.
In this circuit, the output voltage is measured through the voltage divider between R_1 and R_2. This voltage is compared to the reference voltage V_REF. The resulting error signal will control the conduction of the pass element such as the transistor. Therefore, the voltage across the transistor is varied and hence the output voltage across the load is maintained constant.
A Zener diode voltage regulator is a type of series voltage regulator. It can minimize the ripple in the supply voltage and improve the regulation. The efficiency of this type of voltage regulator is low due to the non-zero Zener resistance and it can be improved by limiting the Zener current.
The circuit diagram for Zener Diode Voltage Regulator is shown in the figure below.
The main advantage of the series voltage regulator is that the amount of current drawn is effectively used by the load. It does not draw the full current even when the load does not require any current. As a result, the series voltage regulator is considerably more efficient than a shunt voltage regulator.
The efficiency of the series voltage regulator is relatively low as compared to the switching voltage regulator. But it has the advantages of simplicity and also their output is free of switching spikes.
Shunt Voltage Regulator
In a shunt voltage regulator, regulating element or active pass element such as a transistor is connected in parallel with the connected load. Further, a voltage limiting resistor is connected in series with the load. In order to maintain the constant output voltage across the load, the level of current must be drawn through the series resistor.
The circuit diagram for a typical shunt voltage regulator is shown in the figure below.
In this circuit, the conduction of the transistor is controlled based on the feedback and reference voltage. The circuit is designed in such a way that current through the series resistor remains constant. As the current through the transistor is varied, the output voltage across the load remains constant.
In comparison to the series voltage regulator, the shunt voltage regulator is slightly less efficient but it has a simpler implementation. A shunt voltage regulator is used in very low-powered circuits where the wasted current is very small. This type of voltage regulator is very common for voltage reference circuits.
Advantages
The followings are the advantages of linear voltage regulators:
- It is very simple to implement and easy to use
- It gives low output ripple voltage
- It has a fast response time to load
- It has less noise and low electromagnetic interference
- It is more cost-efficient
Disadvantages
The followings are the disadvantages of linear voltage regulators:
- Its efficiency of it is relatively low.
- It gives the output voltage always less than the input voltage i.e. it performs only step down operation.
- It requires a heat sink since it dissipates excess power as heat and becomes extremely hot during regulation.
- It requires large spaces.
Applications
There are many applications of Linear Voltage Regulator. Some of them are as follows:
- One of the most common examples is the mobile charger. The adapter is supplied with an AC signal. However, the output voltage signal is a regulated DC signal.
- Every power supply in the world uses a voltage regulator to provide the desired output voltage. Computers, televisions, laptops, and all sorts of devices are powered using this concept.
- Small electronic circuits rely on regulators to operate. Even the slightest fluctuation in voltage signal can damage the components of a circuit such as ICs.
- When it comes to power generation systems, voltage regulators play an essential part in their operation. A solar power plant generates electricity based on the intensity of sunlight. It needs a regulator to ensure a regulated constant output signal.
