Don’t let an unexpected voltage spike or power outage wipe out all of the progress you’ve made on your design. With an uninterruptible power supply (UPS), you can save your project from disaster. We’ll tell you exactly why and when to use a UPS, then break down which type best fits your needs.
What is an Uninterruptible Power Supply?
The purpose of a UPS is to provide emergency power (usually by a lead/acid battery) to a load when it senses that the input power source has failed. They are different from emergency power systems or standby generators because they provide near-instantaneous protection from power interruption by using a battery (which can be a supercapacitor or flywheel).
The battery itself usually has a short runtime (about 5-20 minutes), but it should be enough to either save all that precious data/progress that you have made, gracefully shut everything down, or fix the problem that caused the outage.
A UPS can be used to protect hardware like data centers, computers, and other electrical equipment where an unexpected surge/sag can cause serious problems like data loss, business disruption, and even injuries or fatalities.
Types of Uninterruptible Power Supplies
There are three types of uninterruptible power supplies: static, dynamic (rotary), and hybrid. Static uses power electronic converters, dynamic uses electromagnetic engines (generators and motor), and hybrid uses – you guessed it – a combination of both static and dynamic. Let’s take a look at how these topologies are commonly used for electronics.
1. Offline/Standby Uninterruptible Power Supply
The offline/standby UPS is the most basic out of the three. It provides light surge protection and battery back-up. During normal operations, it gets its power from its main power source (generally an AC outlet). Once it senses that the main power source goes beyond acceptable limits or fails, it switches to the “offline/standby” battery where it will then go to the DC/AC inverter – as such, there will be a small transfer time between the main power source and battery.
What’s usually in a standby/offline uninterruptible power supply?
Most standby/offline UPS have a switch to either run on the main power source or the battery component. The majority of the bulk is in the battery component, as the main power supply goes to the AC/DC rectifier that charges the battery. After that it goes into a DC/AC inverter to output into the load.
Figure 1: Offline/Standby UPS (green represents the flow of process).
2. Online/Double Conversion Uninterruptible Power Supply
The online/double conversion UPS differs from the offline/standby as the DC/AC inverter is always connected on. This means there will be no transfer time between the main power source and battery, providing greater protection against spikes, sags, electrical noise, and complete power failure.
What’s usually in an online/double conversion uninterruptible power supply?
The main power source in double conversion UPS goes into the AC/DC rectifier even during normal operations, so it must go through a DC/AC inverter every time, hence the term “double conversion.”
Figure 2: Online/Double Conversion UPS (green represents the flow of process).
3. Line-Interactive Uninterruptible Power Supply
The line-interactive UPS has a similar design to the offline/standby, but with properties of an online/double conversion as well. The line-interactive design can handle small under-voltages and over-voltages (about 20% from its standard voltage) by using a multi-tap variable voltage autotransformer or buck-boost converter. Even during these small under/over-voltages, the battery is not being used and is still being charged until there is a big under/over-voltage.
What’s usually in a line interactive uninterruptible power supply?
The design is similar to offline/standby, but it either has an autotransformer or a buck-boost converter on the main line. This will either boost the voltage for under-voltages or buck the voltage for over-voltages.
Figure 3: Line-interactive UPS (green represents the flow of progress).
Uninterruptible Power Supply Comparison
We created a simple table that breaks down the pros and cons of each of each type of uninterruptible power supply.
Bottom line:
Offline/standby UPS is the most basic, and they are good for applications like home computers, printers, or scanners.
Online UPS is the most reliable and offers the best protection, making them ideal for motor applications or situations where you can’t afford any transfer time. Best uses are for data centers or intensive care units.
Line-interactive UPS would be suitable for light sag and surges, plus it has lower electric consumption. If you want a reliable, efficient, and cost-effective UPS, the line-interactive is the way to go.
* To search for a specific type of UPS (Line-interactive, Online, Offline), use the parametric search bar on the UPS page, navigate to the UPS Type section and search for the desired UPS type.