Uninterruptible Power Supply Working Principle

Uninterruptible Power Supply
Uninterruptible Power Supply

Uninterruptible Power Supply or Source short well-known as UPS. It is an electronic device that can store electricity for a short period of time and provide emergency power supply to various loads such as computers or other devices when the input power normally fails.

A UPS fluctuates from the emergency power system that it supplies to provide immediate protection from I/P power interruptions by storing energy in batteries, and supercapacitors. Like IPS it can store electrical energy in batteries and convert DC power to AC current. The battery run time of most UPS is relatively short but long enough to start a standby power source.

UPS is generally used to provide protection to equipment such as computers, electrical appliances, and data centers in case of power failure. Typically a UPS is capable of providing backup power with a switching time of 0.1 seconds. As a result, the user’s electronic devices like computers or other data storage devices will not be reset or restarted. In computers or electronic devices, UPS is used as backup power for short periods of time. Mainly, this device keeps a computer running for short periods of time after a power outage and protects data on the computer.

Nowadays, different types of UPS systems are coming with software components that enable you to take automobile backup in case of a power outage while you are away from the computer.

Block Diagram of Uninterruptible Power Supply

UPS Block Diagram
UPS Block Diagram

A UPS has major five-part, such as:

  • Rectifier,
  • Inverter,
  • Battery,
  • Static Switch,
  • AC Filter;

Let’s discuss a brief about them-


A rectifier is an electrical device consisting of one or more diodes that convert alternating current (AC) to direct current (DC). The method by which rectification is done is called rectification. The method by which rectification is done is called rectification.

In UPS, the rectifier works to convert the supply AC to DC. Here first the supply AC voltage converts to DC, a part of the converted DC voltage charges the battery bank, and the other part goes to the inverter circuit.


This is an electrical device that converts direct current (DC) to alternating current (AC). Converted AC can be operated at any voltage and frequency system by means of suitable transformers, switches, and control circuits.
In UPS, the inverter circuit converts the DC voltage from the rectifier to AC and feeds the converted AC to the filter block.

Static Switch:

The term ‘static’ corresponds to something that does not change or is fixed and a ‘switch’ is used to make or break a connection in an electrical circuit. A static switch is a device that performs a switching operation without the presence of moving parts.

Typically, power semiconductor devices that have the ability to turn on or off in a fraction of a microsecond find applications as fast-acting static switches. In high-power applications, thyristors are used while In low-power applications, power transistors are generally used.

The working of a Static Switch is also known as Static bypass mode. In this mode, the static bypass switch is usually for providing the output. UPS goes to this mode when the inverter fails or the inverter overloads.

AC Filter:

A filter circuit is normally used to purify the flow of current. Some DC remains present in the AC current obtained from the inverter. So this impure AC current is converted into pure AC current using a filter circuit.


The unit or device or machine that converts chemical energy into electrical energy is called a cell or electrical cell. And when multiple cells together form a device, it is called a battery. The major role of batteries is to store electricity.

In the Uninterruptible Power Supply, the Battery store electricity that it supplies when the main power supply is off.

Types of UPS:

Electrical power supply intrusions can come in many forms such as surges, voltage dips, voltage spikes, and harmonics. These problems can cause serious damage to electrical gears at most manufacturing stages or during the critical processing of an operation.

To reduce the risk of power supply distortion, UPS systems are often integrated into electrical networks. Electronic power supply equipment manufacturers can provide consistent, high-quality power currents for a variety of electrical load gear, and these devices are commonly found in industrial processing applications, medical services, emergency gear, telecommunications, and computerized data systems.

An Uninterruptible Power Supply system can be a helpful device to ensure proper power supply performance.

Generally, Uninterruptible power supply devices, or UPS are classified into three types. Such as:

  • Standby UPS
  • Line Interactive UPS
  • Online UPS

1. Standby UPS

Standby UPS
Standby UPS

A standby uninterruptible power supply also called an off-line UPS, is commonly used for PCs. Because this device provides battery backup and protects again power surges in the event of a power outage. The block diagram of this UPS is shown in the above picture.

This UPS device includes a battery, an AC or DC converter, and DC or AC inverter, a static switch, an LPF which is used to reduce the switching frequency from the O/P voltage, and a surge suppressor.

The standby UPS system works with a switching system of AC. It is interrupted to select the I/P as the primary power source and interconnect with the battery and inverter as the backup source in the case of primary power.

The inverter passes AC power through the unit under normal conditions and switches to battery mode when the power fails to occur.

This type of UPS system offers a small size, a high degree of efficiency, and quite a low cost, making this UPS easy to build.

2. Line Interactive UPS

Line-Interactive UPS
Line-Interactive UPS

The above image is the block diagram of a Line Interactive UPS, the most common UPS used for small businesses. The design of line interactive UPS is similar to that of standby UPS. With battery backup, this UPS provides conditioned power, eliminating voltage fluctuations.

Also, the UPS passed AC power through a voltage regulator that corrects low and high voltages as needed and switches to battery backup mode when a power failure is detected in the main power supply.

It is a low-cost, and high-efficiency UPS that can make in the power range of 0.5-5kVA

3. Online UPS

Online UPS
Online UPS

The above image is the block diagram of Online UPS. Online UPS is also known as a double conversion online uninterruptible power supply. This is the most commonly used UPS. The design of this UPS is similar to standby UPS, except that the primary power source is an inverter instead of AC mains.

In the UPS first, the supply AC power is converted to DC and then back to high-quality AC power, free of voltage fluctuations and other distortions common to the grid power. It also has a high-efficiency ECO mode that automatically resumes or suspends double conversion depending on input power quality.

Important Consideration Before Buying UPS.

Not only in the case of UPS, before buying any electronic product we should know about that product well. We should buy that product after knowing well what I am going to buy it for and how much the tolerance and performance of the product are. In most cases, UPS is used to support the computer. In that case, buying a good quality UPS is a must.

What you need to do at the beginning of buying UPS and IPS is a load calculation. First, you need to calculate how much load you want to run with the UPS.

1. Load Calculation:

We will try to understand this with a small example. Similarly, you can calculate your required load.

Suppose, I will buy a backup device or UPS for two lights and two fans, and one PC.
Both lights are 35 watts, so light = (35x 2) = 70 watts.
And, if the fan is 80 watts, Fan = (80x 2) = 160watt.

Typically 30 to 70 watts need depending on the PC model. Let’s consider my PC is 50W. So, PC = 50 watts.
So, Total load = (70+160+50)= 280 watt.

Note that in the market you will find UPS or IPS devices with VA ratings. As we know, the difference main between VA and Watt is the power factor, which normally considers 0.8.

We know that the ratio of W to VA is the power factor.
So, Power factor => PF = W / VA;
Equivalent equation of VA = Watt x 0.8;
So, VA = (280 / 0.8) = 350 VA;

To increase UPS life and load safety the value of VA should be increased by 20% to 25% over the demand load.

So Total VA = (350 +25%) = 437.5 VA
Now you can buy any UPS of close value in this value.

2. Backup Time Calculation:

A backup device consists of two parts, one of which is the electronics part that charges the battery and converts power from the battery to the load when needed. The load calculation that we did above is basically the calculation of the electronic part. The load calculation value “Total VA” means how much load you can use at once.

Another part of the UPS is the backup time which mainly depends on the battery size. This means the size of the battery will determine how long your UPS will provide power backup.

The battery backup time formula is:

Back up time = (Battery AH x Volt x N x 0.8) / Load

Battery AH = Battery Amp Hours,
Battery quantity = N,

As we know, all electronic devices available in the market are rated in KiloVolts. But in the case of batteries, the rating is given at voltage. So 0.8 will multiply with the total volts.

On the other hand, in the case of batteries, ampere-hours mean the current capacity of the battery and how much amperage the battery can supply per hour.

Let’s say the size of the battery we have taken is 12 volts, ampere 60 AH.

So, we can write,
Battery AH = 60Ah,
Voltage = 12V,
N = 1,

So, Total Back Up Power = (60 x 12 x 1 x 0.8) = 576 watt.
576 watts means this battery can give you 576 watts in one hour.

The formula for determining backup time = Backup Power / Demand Load.
The total VA we got in the above load calculation is the demand load or load.

So, total backup time = (576/437.5) = 1.3 hours
That means this UPS can give us a backup time of 1 hour and 20 minutes.

So, if you want to increase the backup time, simply increase the size of the battery voltage.

3. Check the Sine Wave:

In the post Uninterruptible Power Supply this picture is about Pure and Modified Sine Wave
Pure and Modified Sine Wave

In the above image, we have mentioned 2 sine waves, the first is a pure sine wave and the second is a modified sine wave.

Before buying a UPS or IPS, the sine wave of the device must be checked, it is a difficult process, and it cannot be checked without an oscilloscope, but it is important. So, confirm by discussing with the company that the UPS or IPS is a pure sine wave device.

You must be wondering what if I don’t test it or buy a modified sine wave UPS? Let’s discuss this-

Consume More Power:

First, if you take a modified sine wave UPS, it will consume more power to charge the battery than a pure sine wave UPS.

Studies have shown that a modified sine wave IPS or UPS consumes 20% more power than a pure sine wave IPS or UPS to charge the same-rated battery.

Risky for Sensitive Devices:

Second, a modified sine wave is vulnerable to sensitive devices. Because the pure sine wave voltage rises and falls smoothly with varying phase angles and changes its polarity instantaneously when it crosses 0 volts.

But in the case of a modified sine wave, the voltage rises and falls suddenly and the phase angle also changes suddenly. Also, it sits at 0 volts for a while before changing its polarity. So, the voltage range always changes suddenly like suddenly 250v, 210v, etc.

If you use a PC or TV-type device on a modified sine wave UPS, it will shorten the life of your device. Also, if a fan or motor-type device is run, it will create noise. That plays a role to increase the electricity bill.

So the solution is to buy a UPS or IPS from a reputable company.

4. Charging Time of Battery:

Perfect charging holds battery life for a long. A battery needs a certain amount of time to fully charge ( which is equal to Battery AH/10). So discuss this with the supplier company before buying the UPS and battery.

To calculate the battery charging time use the formula given below:

Battery charging formula = (Battery AH/10);

In the above, we have taken a 60AH battery,
So, battery charging formula = (60/ 10) = 6 hours;

This means the battery needs 6 hours to fully charge. So, at this point check if the UPS or IPS charging system is able to perfectly charge your battery.

How UPS Should be Used.

Many of us use UPS to provide power support to computers, so UPS should be bought from a better brand. let’s know how UPS should be used-

  • It is best to never switch off the main power of the UPS.
  • Do not turn off the UPS even if the power goes out.
  • Every month at once UPS should be fully discharged and fully charge.
  • In the case of CRT (cathode ray tube) monitors, never turn on the monitor when the power goes out. Turning it on puts stress on the battery that causes of shortens the battery life.
  • Never use a load higher than the design load of the UPS.
  • Occasionally clean the UPS battery connectors if possible.
  • In most cases, the battery in the UPS is dead. So pay more attention to the battery. If you replace the old battery of the UPS with a new battery instead, you will find that it is providing the same service as before.

Difference between IPS and UPS

Many of us have questions about the difference between IPS and UPS. Especially many people ask whether fans, lights, etc. can be run with UPS. Here, we have shared some ideas based on these topics.

1. KVA Rating:

IPS power is usually 16kVA and is 3 phase whereas UPS power is 2kVA.

2. Switching Time:

IPS takes about 500 milliseconds to transfer power from the main supply to the battery or from the battery to the main supply, while UPS takes only 3 to 8 milliseconds.

3. Voltage Range:

IPS provides the same voltage as the main supply voltage but UPS has automated voltage regulation and it is usually set at 220 volts.

4. Mains Supply Power:

IPS is directly connected to the main power supply. This mains supply also goes to the output at the same time which means at the same time the mains supply charges the battery and powers the output. The IPS has a sensor and relay mechanism that always checks whether power is coming from the main supply. Whenever the mains power goes off, It is triggered and starts discharging the battery.

In the case of UPS, first, the current is supplied directly to the UPS from the main supply. The AC current is converted from AC to DC and starts charging the battery. Power from the charged battery goes to the sine wave inverter where DC is converted to AC. From this AC we mainly get power to the PC or other devices. Though the output power comes from DC, its time difference never changes. So its frequency always remains unchanged.

5. Best for Devices:

Mains supply current is basically 100% sine wave. The output of IPS looks a lot like a step waveform. To the lack of pure sine wave loss of inductive load occurs on IPS. This is why we often hear that the IPS regulator is often damaged.

The mechanism of IPS is much less expensive and complex than that of UPS.



This is about what is UPS (uninterruptible power supply), a block diagram of UPS with an explanation, and the types of UPS. We hope you understand the concept of UPS better. Furthermore, for any queries or electronics projects related to this topic, please give your feedback by commenting in the comment section below.


Leave a Reply

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