Voltage Regulators

In electrical circuits, we sometimes need a stable voltage across a particular load. The voltage across the load should not vary due to changes in the input voltage or due to the load itself. For such applications, we need a voltage regulator. Today we are going into the nitty gritty of voltage regulators and we are going to study the different types of voltage regulators.
When a reliable source of voltage is required, we use a voltage regulator. It has a very simple feed-forward design and uses negative feedback loops. Refer to the diagram below to understand more:

Unregulated voltage enters the controller. A part of the output is fed to the sampling circuit, which in turn feeds it back to the comparator circuit. The voltage level is compared with the reference voltage. Appropriate corrections are made and send back to the controller. In this manner, the voltage is regulated.

Different types of Voltage Regulators

There are mainly two types of voltage regulators:

  1. Linear voltage regulators
  2. Switching voltage regulators

Linear Voltage Regulators

Linear voltage regulators operate like a voltage divider. It uses the FET in the ohmic region. The resistance of the linear voltage regulator changes with the load and gives a constant voltage output. Below is a picture of LM7805, one of the popular linear voltage regulator. They are based suited for low cost low power applications.
There are two types of linear voltage regulators:

  • Series Voltage Regulator
  • Shunt Voltage Regulator

Series Voltage Regulator

A simple series voltage regulator has a variable element like a transistor whose resistance varies on a variable input voltage, thereby keeping the output voltage constant and steady.
series voltage regulator

Shunt Voltage Regulator

This works similar to the series voltage regulator but is connected in the circuit in parallel or in shunt connection. All the excess voltage is sent to the ground. Shunt voltage regulators are mainly used for precision current limiters, voltage monitoring, error amplifiers etc.
shunt voltage regulator
To summarise, here are the advantages and disadvantages of linear voltage regulators

Advantages of Linear Voltage Regulators

  • Cheap
  • Lower electromagnetic interference and noise than switching voltage regulators.
  • Provides constant output voltage for low power applications

Disadvantages of Linear Voltage Regulators

  • Very inefficient
  • Needs additional heat sink due to the amount of heat generated
  • Can’t get an output higher than the input.

Switching Voltage Regulators

Switching voltage regulators uses a controlled switch to regulate the voltage hence the name. They are used where there is a large difference between the input and output voltage. They are more efficient but introduce greater complexity in the circuitry.
switching regulator circuit
Switching regulators switches on and off rapidly to change the output according to the requirement. They use transistors which turns on and off depending on the desired voltage level.
There are different ways in which switching regulators can be used :

Boosting (step-up)
This is used to produce a higher regulated output voltage by boosting the input voltage.
boosting switching regulator circuit
In the image above, a 5V input is being boosted to 12V output.

Bucking (step down)
This is used to produce a lower regulated output voltage than the input voltage.
bucking switching regulator circuit
In the image above, an 8-40V is being stepped down to 5V output.

Boosting/Bucking (Inverter)
In this configuration, both stepping up and stepping down the regulated output voltage is possible. This is used if there is a requirement for increasing or decreasing the output voltage from time to time. Inverting the output voltage is also possible.
Switching regulators are used where power efficiency is a big concern and when higher or lower output voltage is needed.

Advantages of Switching Voltage Regulators

  • It has higher power conversion efficiency than linear voltage regulators
  • Do not require heat sinks
  • Can be used when there is a huge difference between input and output voltage.

Diadvantages of Switching Voltage Regulators

  • Produces more electromagnetic interferrance and noise.
  • Is more complex.
  • More costly.

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