What is a linear power supply, Building a linear power supply in Proteus.


Majority of the electronic appliances we use in our homes use direct current, DC. Since the power supply to our homes is alternating current, we have to look for a way to convert this alternating current to a direct current. To do so, we use a device called a power supply. There are two basic types of power supply, namely:

  1. Linear power supply
  2. Switch mode power supply (SMPS)
Switch mode power supply SMPS
Switch mode power supply

The switch mode power supply is more complex than the linear power supply, but more efficient and energy conserving. However, there are devices where the linear power supply is preferred to the switch mode power supply. In devices that use radio signal, the use of switch mode power supply is not recommended. This is because, the high frequency oscillation produced by the switching transistors in the switch mode power supply interferes with the radio signal in the device, hence it is recommended to use linear power supply in such devices. Power supplies come in form of battery chargers and wall warts, which are mostly switch mode power supplies. The linear power supply nonetheless has its advantages, it is very cheap and easy to construct, in addition to no high frequency noise emission.

In this tutorial, we shall design and simulate a linear power supply in Proteus, and then discuss the switch mode power supply in subsequent tutorials.

How to download and install proteus free

What is a linear power supply?

Linear power supply as the name implies means a power supply that has its input power linearly related to its output power. What this means is that, as the input power increases, the output power increases too, and as the input power decreases, the output power decreases too.

The parts required to design and simulate the circuit include:

  1. AC voltage source
  2. 220V to 12V transformer (1)
  3. Bridge rectifier (1)
  4. Capacitor 10uF (1)
  5. Capacitor 1uF (1)
  6. Voltage regulator IC 5V (1)
  7.  Switch (1)
  8. Resistor 100Ω (1)
  9. LED (1)
  10. Bread board
  11. Jumper wires

Before we delve into the design, let’s have a brief description of the various parts we listed above for the design.

Parts used in making Linear Power supply

What is a transformer?

A transformer can be defined as a passive electronic component or device that transfers electrical energy between circuits, through the process of electromagnetic induction.
A transformer can come as a Step-up transformer, where a smaller voltage value is transformed to a lager voltage value. Or a buffer transformer, which serves as an isolation device between two circuits, or a Step-down transformer, in which voltage is reduced from a higher value to a lower value, and it is this type of transformer we shall use to design our linear power supply.

Step-down transformer

What is a capacitor?

A capacitor is an electronic component that stores energy in form of electrical charges. It is used in so many electronic circuit designs to accomplish tasks like, filtering, oscillation, amplification, power back-up, etc. I have written a comprehensive tutorial on what is a capacitor, types of capacitors and more, you can check the tutorial here.


What is a regulator IC?

This is an integrated circuit that is basically used to regulate unregulated voltage coming out of a rectified AC voltage. It comes as TO220 package, and in various regulated positive and negative voltage values. It also comes as a variable voltage regulator, where can set it up to produce variable regulated voltage values. However, the voltage regulator IC is commonly known to come as the 78XX series and the 79XX series. The 78XX series is the positive voltage series that produce regulated positive voltage, while the 79XX series is the negative voltage series that produce negative voltage. Hence, we have:
7805, 7809, 7812, 7815, 7824 for the positive voltage series and 7905, 7909, 7912, 7915, 7924 for the negative voltage series.
At the other hand, the variable voltage regulator IC can produce output voltage between 1.27V to 37V. see image below:

7812 Linear voltage regulator

What is a switch?

A switch on one hand can be likened to a bridge that facilitates current flow between two discontinues points in a circuit, a switch is basically an electricity conductor. Before a material is used as a switch, it must be ascertained that the material is an electric conductor with a negligible electrical resistance. On the other hand, a switch can be seen as a gate that opens the path for current flow in a circuit. Below are simple images of a switch.

types of switches
Various types of switches

What is a resistor?

A resistor is an electronic component that acts to limit the rate of current flow in a circuit. Although every electronic component has some kind of electrical resistance inherent in them, however, we have electronic components that are purely dedicated to doing the work of electrical resistance. They come in different forms and sizes; they also come in different values. This makes it easier for the circuit designer to use them in an electronic circuit design. I have made a comprehensive tutorial on resistor and resistor color codes; you can check them out here. Below is a typical example of a resistor.

what is resistors
Types of resistors

What is a light emitting diode?

A light emitting diode, or an LED is a type of diode that emits visible light when the right amount of voltage and current is passed through it. An LED comes in different shapes and sizes. It also comes in different colors, and these different colors correspond to different voltages. An LED is an electronic component that is very sensitive to voltage. Hence, it is always connected in series with a resistor called, a current limiting resistor. It is always advisable to connect a current limiting resistor to an LED in any electronic circuit.

different types of LEDs
Types of LEDs

What is a bread?

A breadboard is a tool used in electronic circuit design to connect the legs of electronic components. It comes in various sizes, colors and shapes. To learn more about what is a bread and how to use a bread board, check this my elaborated tutorial. See a bread image below.


What is Jumper wire?

A jumper wire is used along side a breadboard to connect electronic components in a circuit. Jumper wires come in different colors and forms, we have the male-to-male jumper wire, the female-to-female jumper wire and the male-to-female jumper wire. See images below.

Jumper wires

Now that we have listed and explained the various parts we will use for the simulation and design, let’s delve into the design of the linear power supply. The circuit diagram is as shown below.

Linear Power supply
Linear Power supply

Circuit explanation of a linear power supply

The above diagram is a circuit diagram of the linear power supply we are to design. This circuit was designed in Proteus design suite, and the simulation was also made in Proteus design suite.

The design of a linear power supply has stages, they are listed below:

  1. Voltage step-down transformation stage
  2. Voltage rectification stage
  3. Voltage filtration stage
  4. Voltage regulation stage

Voltage stepdown – Linear power supply

This stage requires the transformation of the 220V AC voltage to 12V with the help of a step-down transformer. When this is done, the output voltage from the transformer will retain the same waveform as the input voltage to the transformer.

Voltage rectification – Linear power supply

After the 220V AC has been stepped-down to 12V, the stepped-down voltage is then rectified from an alternating voltage to a direct voltage with the help of the bridge rectifier. However, in the process of the rectification, some of the voltages from the transformer is used up energize the bridge rectifier. See the waveform of the rectified voltage below.

what is a linear power supply
Rectified voltage signal

Voltage filtration – Linear power supply

The next stage after rectification is filtration. Rectification results to the creation of undulating direct output signal. This undulating waveform is then filtered out with the help of a capacitor. This capacitor is called filtering capacitor. The filtering capacitor adds up its charged voltage to the output voltage of the bridge rectifier, and that increases the filtered voltage of the system. See image below

what is a linear power supply
Filtered rectified voltage

Voltage regulation – Linear power supply

The next stage in the design of the linear power supply is the voltage regulation stage. In this stage, we use the 7805-voltage regulator IC to regulate the output voltage from the filtration to stable 5V, that we can use to power up any device that works with 5V. And after the we have connected the voltage regulator IC, we connect an extra capacitor to the voltage regulator IC, this is to help filter out any other remaining AC voltage ripples at the output of the system. When all this is done, we will then obtain a near-perfect DC voltage from the linear power supply device.

You can watch the video of the simulation below.

This is how to design and simulate a linear power supply. In the next tutorial, I will make a video showing the real design. so, visit later to check out the design. in the meantime, check out other tutorials I have made in the past below.

How to make a sine wave inverter in Proteus
How to make Bluetooth controlled scrolling text display
How to make water level indicator and control

Leave a Reply

Your email address will not be published. Required fields are marked *