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What is a Transformer?

Author: Apogeeweb Date: 15 Jan 2021  82

Transformer Symbols


If you've been around electrical equipment for a long time, you may have heard of the transformer. Yeah, they're the enormous bulky things found in the corners of the street that make random scary noises and spit sparks sometimes. There is also a sort of small transformer in your phone charger, but much, much smaller and with a different mechanism.


Ⅰ Introduction

Ⅱ Transformer Definition

Ⅲ Importance of Transformers in Electrical System

Ⅳ Transformer Symbols

Ⅴ Working Principle of a Transformer

Ⅵ Transformer Properties

Ⅶ Transformer Construction

  7.1 BOBBIN

  7.2 CORE


Ⅷ Transformers Application

Ⅸ Conclusion


 Transformer Definition

A transformer is a device that converts one voltage or current to another using the principles of electromagnetism. It consists of a pair of wounds around a magnetic core of the insulated wire. The winding to which the voltage or current to be converted is connected is called the primary winding and the secondary winding is called the output winding.


Transformers come in two types: step up, which increases the voltage or current, and step down, which lowers the input of the voltage or current. The transformers in your microwave oven, for example, are a secondary transformer that is used in the microwave oven to supply about 2200Volts to the vacuum tube.


One thing to remember is that transformers only operate with AC voltages or adjustments and do not work with DC. We'll understand why now.


Importance of Transformers in Electrical System

It was around 1856 that there was a rivalry between two brilliant minds, Nikola Tesla and Thomas Edison. Those were the days when electricity and its applications were merely noticed by glowing a lamp and driving a motor. It was Edison and his associates who first discovered the DC (Direct Current) system, and then Tesla developed his AC (Alternating Current) system sometime after that. The two have since tried to show that their scheme is more advantageous than the other.


The time has come for houses to get electricity by then. Although Edison was busy showing how dangerous AC is by electrocuting elephants, Tesla and his team came up with the transformers that made it much simpler and more effective to transmit electricity. Also, transformers play a key role in the transmission system today. Let's learn why.


High-voltage and low-current transmission of electricity will help us minimize the thickness of the transmission wires and thus the cost, which will also improve the system's performance. For this purpose, a typical transmission system may be anywhere from 22KV to 66KV, although some generators have an output voltage of only 11kV in the power plant and need only 220V/110V for the household AC unit. So where does this transfer of voltage take place and who does it?


Transformers are the answer to the issue. There will be transformers in the system from the power plant to your home that will either step-up the voltage (increase voltage) or step-down (decrease voltage) to preserve the system's efficiency. The transformers are therefore referred to as the heart of an electrical transmission system. In this post, we will be learning more about them.


 Transformer Symbols

For a transformer, the circuit symbol is simply two inductors placed together side by side that share the same center. The type of core used is shown by the existence of the line between the two windings: a dashed line represents ferrite, two parallel lines represent laminated iron, and no line represents the core of air.

Transformer symbols

The number of 'bumps' is often used as a rough measure of the role of the transformer-less bumps on one side and more on the other which means that there is a lower number of turns on the first side than the other.

 Working Principle of a Transformer

We need to go back in time, to the laboratory of Michael Faraday, to understand the operation of a transformer. Perhaps the father of the transformer can be named Michael Faraday, as it was his experiments that helped us understand electromagnetism and create devices such as motors and generators.


There was a race to try to create a practical system that could harness the strength of magnets to produce electricity in the late 1800s when it was discovered that electricity and magnetism were related phenomena.


Faraday figured out that by bringing a magnet close to a coil of wire, electricity could be produced. What he discovered was that only when the magnetic field shifts can the voltage be produced, that is, whether either the coil or the magnet is shifted relative to the other.


In DC, the movement of the current is constant and so is the magnetic field. There is no voltage generated on the secondary because the field is constant and not changing and the transformer just looks like a regular coil of resistive wire to the power supply. So, with DC currents, transformers do not operate.


He also found that a current flowing in one coil might cause the current in the other coil when two coils of wire were held close to each other. This definition is referred to as mutual inductance, which governs the operation of all modern transformers.

working principle of transformer

The transformer consists of two windings wound on a magnetic core, as shown in the figure.


The goal of having a core is that air is not a very good magnetic field supporter, so having a magnetic core increases the magnetic field for a certain amount of current flowing through one winding, which in turn generates a stronger current in the other, improving the device's overall performance.


A magnetic field is built up in the core as a current moves through the primary and is limited mostly to the core. This magnetic field passes through the center of the secondary and, thus, the law of reciprocal induction causes a current in the other.


The beauty of this method is that the ratio between the input voltage and the output voltage is simply the ratio between the main and the secondary windings, summarized by the following formula:

Vout/Vin = Nsec/Npri

Vin is the input voltage, Nsec is the number of turns in the secondary winding, and Npri is the number of turns in the main winding, where Vout is the output voltage.

So if you have two transformers, one with 100 turns on the primary and 1000 turns on the secondary and one with 10 turns on the primary and 100 turns on the secondary, you can measure the ratio of turns to be 1:10 on both of them, so that they both increase voltage to the same degree.


 Transformer Properties

If we take a closer look at the above example, the first transformer would have higher winding resistance (since more wire is used) and will restrict the amount of current that can be drawn from the transformer in certain instances. This property is called winding resistance, but since the copper wire used normally has a low resistance, it does not matter in most cases.


Another thing you see is that the main and secondary windings have no direct electrical connection. This is called galvanic isolation and, as we can see, can be very useful. Looking at each of the transformer windings, we can see that they are shaped like inductors and also have an inductance, a coil of wire wrapped around a magnetic center.


This inductance, given by this formula, is proportional to the square of the number of turns:

Lpri/Lsec = Npri2/Nsec2

Where Lpri is the primary winding inductance, Lsec is the secondary winding inductance, Npri is the number of turns on the primary windings and Nsec is the number of turns on the secondary windings.


The proportionality constant can be found in the datasheet for a given core and is typically given in μH/turn2 units. The exact value is based on the core form and scale.


Suppose you have a transformer core with a 1uH/turn2 specification. If you wind one winding on that heart, the value of the constant multiplied by the number of turns squared will be the inductance, in this case, 1. So the winding inductance of that one will be 1μH. If you wind the same core with another winding with 10 turns, then the inductance will be:

(1µH/turn2)*(10 turns)2 = 100µH

Since the windings have inductance, they provide an impedance to AC signals, given by the formula:

XL = 2π*f*L

Where XL is the impedance in ohms, f is the frequency in ohms and L is the inductance in Henries.

Say, you want to design a transformer at 50Hz, which is the standard power line frequency, that draws 3A at 220V AC. Then, by Ohm's law, the impedance of the main will need to be 73.3 Ohms. Now that we know the appropriate impedance and the frequency, we can rearrange the formula to find out the inductance required for the winding:

L = (XL)/(2π*f)

Substituting the values, we find that 233mH would be the required inductance.

We can calculate the windings necessary to get the inductance needed using this information and the value of μH/turns2 from the datasheet.

Assuming the value is 50μH/turns2, we can rearrange the formula to evaluate the inductance:

transformer number of turns

Where N is the number of turns, L is the inductance required, and the term t2/μH is just the inverse of the value of the datasheet.

We get the necessary number of turns of 2158 when adding our values to the formula. So, as you can see, you can build transformers for almost any application once you get the hang of the formulas!


 Transformer Construction

An awareness of transformer construction is vital for someone who wants to wind their own transformers.

A transformer is made up of a few fundamental components:



Bobbin transformer

For every transformer, the bobbin is the fundamental structure. It provides a spool on which the windings will wind and keeps the core in place as well. It is typically composed of plastic that is heat resistant. It also sometimes involves metal pins onto which, for example, you can weld the ends of the windings if you want to mount it to a PCB.


7.2 CORE

Perhaps the most significant aspect of the transformer is this. The cores can come in several shapes and sizes, as seen in the image. It is the core's magnetic properties that decide the transformer's electrical properties that are built around the core.



copper wire

The wire used in the house, though it can seem like a trivial item, is as critical as any other element. In general, solid enameled copper wire is used because the insulation is strong and thin, so plastic insulating sheaths do not waste space.


 Transformers Application



This is possibly the most common transformer application, stepping down the mains voltage for low voltage devices. This stuff, like microwaves and old TVs and wall brick power supplies, you might even find inside. These transformers have iron cores that make them bulky and much less efficient than other types, providing excellent permeability.

Three secondary wires mark them as 12-0-12 or 6-0-6. If you make the center wire the ground reference, this means that the outer two wires have an output of 12V AC RMS. If you calculate the 12v winding over each, you get 24V AC RMS. This gives you the flexibility to use the transformer as you may like.



These are very specific type of power supplies that generate a DC output and take a DC input. Both modern phone chargers are located here. The transformers used in these PSUs are shaped more like medium- to high-permeability inductors with a limited number of turns and ferrite cores. For a brief period, a DC voltage is applied across the 'primary' so that the current ramps up to a certain amount and retains some magnetic energy in the core. At a lower voltage, this energy is then passed to the secondary, since it has a smaller number of turns. They work and achieve outstanding efficiencies at high frequencies and are very thin.



There are special transformers with a 1:1 turn ratio, such that the voltages of the input and output are the same. They are used to decouple equipment from the earth's mains. Since mains are referred to as earth, touching even one wire will lead to a shock since the return path is simply the ground. The unit is separated from the main earth by the use of isolation transformers, as transformers are galvanically insulated.




Many countries use 220V AC as the normal supply voltage around the world, but some countries use 110V AC, such as the US. This means that it is not possible to operate certain devices such as blenders in all countries. To this end, transformers that convert from 110V to 220V or vice versa can be used to ensure that appliances can be used in any region.



There are unique transformer types that are used to balance the source and load impedance. RF and audio circuits are commonly used.

The ratio of turns is equal to the source's square root and load impedance.



This is a special type of transformer that has only one winding that forms the secondary with a 'tap' output. This tap is normally variable, so the output AC voltage can be varied, much like a voltage divider.



Transformers are useful instruments and it can be very useful to learn how to build and operate with them! Although we have covered the basics here, it is something that can be discussed in another whole article to build a transformer right from scratch, so for some other time. But now, you'll know why it's there and how it works when you see a transformer again.



1. How does a transformer convert AC into DC?

Transformer is not designed to convert ac to dc. It is pure AC device used to step down/up voltage levels keeping frequncy,power,FLUX constant. In mobile charger we use transformer along with bridge rectifier to convert domestic AC supply to dc .(with ripples) Finally,such a transformer which convert ac to dc is not designed yet.

2. Will a transformer work with DC?

Transformers work in the principle of Faraday's law of “mutual induction”, in which an EMF is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding.

As in DC(voltage being always constant) the change in flux is zero so no mutual induction,thus transformers can't work with a DC supply. Moreover if DC of similar rating of AC(Voltage & Current) is fed into the terminals of a Transformer there is a high possibility that it would burn the primary coil.

Ordering & Quality

Photo Mfr. Part # Company Description Package PDF Qty Pricing
HX5004NL HX5004NL Company:Pulse Electronics Network Remark:Isolation and Data Interface (Encapsulated) Pulse Transformer 1CT:1CT Transmitter, 1CT:1CT Receiver Surface Mount Package:N/A
In Stock:On Order
1+: $10.76000
10+: $8.24400
25+: $6.98440
50+: $6.87000
100+: $6.52650
250+: $6.45780
500+: $6.36620
1000+: $6.29750
5000+: $6.18300
T1094NL T1094NL Company:Pulse Electronics Network Remark:TRANSFORMER TELECOM DUAL T1/E2 Package:40
In Stock:517
1+: $5.02000
10+: $4.06600
25+: $3.28720
50+: $3.07940
100+: $2.94100
250+: $2.85452
500+: $2.76800
1000+: $2.68150
5000+: $2.46525
H1102 H1102 Company:Pulse Electronics Network Remark:LAN Pulse Transformer 1CT:1CT Surface Mount Package:N/A
In Stock:On Order
HX5004ENLT HX5004ENLT Company:Pulse Electronics Network Remark:PULSE XFMR 1 CT:1CT TX/RX 350UH Package:300
In Stock:On Order
300+: $6.45780
HX1188 HX1188 Company:Pulse Electronics Network Remark:Isolation and Data Interface (Encapsulated) Pulse Transformer 1:1 Transmitter, 1:1 Receiver Surface Mount Package:N/A
In Stock:On Order
HX5084NL HX5084NL Company:Pulse Electronics Network Remark:330µH Pulse Transformer Surface Mount Package:N/A
In Stock:On Order
1+: $6.50000
10+: $4.94000
25+: $4.81000
50+: $4.42000
100+: $4.16000
250+: $4.03000
500+: $3.90000
1000+: $3.77000
5000+: $3.64000
HX1148NLT HX1148NLT Company:Pulse Electronics Network Remark:XFRMR MODULE 1PORT 1:1 10/100 Package:N/A
In Stock:300
300+: $1387.65000
600+: $2727.45000
1500+: $6699.00000
7500+: $32896.88000
15000+: $64597.50000
G506 G506 Company:Tamura Remark:2mH Isolation and Data Interface (Encapsulated) Pulse Transformer 2:1:1 Ter Through Hole Package:N/A
In Stock:On Order
1+: $11.16000
10+: $8.55000
25+: $7.24360
50+: $7.12500
100+: $6.76880
250+: $6.69752
500+: $6.60250
1000+: $6.53125
5000+: $6.41250

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