Online UPS

At present every organization needs 100 percent availability of power. But it is very tough to maintain zero downtime of the power supply. Some of the organizations like hospitals, information security, etc. are serving critical services where the absence of power supply is not acceptable even for 5 minutes. To solve this problem many organizations use their power backup generators. But these backup generators run on fossil fuels like diesel and petrol that cause environmental pollution. One alternative of these power generators is “Online UPS”.

What is Online UPS?

We are already aware of the word UPS that simply represents “Uninterrupted Power Supply”. If don’t, let me remind you, in your old personal computer there is a power backup unit that provides a power supply in absence of mains power. When an incoming power failure occurs then only backup batteries connect to the inverter circuit to generate AC power by using DC power. But “Online UPS” is slightly different from this conventional uninterrupted power supply unit. In an Online UPS, the backup batteries are always connected to the inverter circuitry (DC to AC converter circuit), as of result, it is not necessary to have a power transfer switch or a relay unit (power transfer switch is responsible to connect backup batteries to inverter circuit only on the absence of the main power). In Online UPS when mains power failures, the rectifier circuit (AC to DC converter circuit) just drops out of the circuit and the batteries keep the flow of power steady and unchanged.

Online UPS working diagram

Online UPS working diagram

When mains power comes back, the rectifier circuit resumes carrying most of the load and also starts charging the backup batteries. In most Online UPS, charging current is limited by the high power rectifier circuit to prevent overcharging or heating to backup batteries. The most important significance of the Online UPS over other UPS is its ability to provide an “Electrical Firewall” or “Electrical Surge Protector” between the incoming utility power and sensitive electronic equipment at the load end.

What is inside this gadget?

An Online UPS contains several electronic circuit units. We will see each and every important unit of this gadget. Have a look at below technical parts:

  1. Rectifier
  2. Inverter circuit
  3. Static switch
  4. Display panel
  5. Cooling unit
  6. Backup batteries
internal circuit of an Online UPS

Internal circuit of an Online UPS


The rectifier unit carries out several key functions. The first is to convert the input power from Alternating current (A.C.) to Direct Current (D.C.). And the second important role is to recharge the backup batteries, while DC power routes to the inverter too.

Depending on the load handling capacity of the online UPS, the rectifier unit also incorporates the battery charger. The rectifier circuit can accept the wide input voltage fluctuations or it can handle overload or surges without having to engage the backup batteries.

Inverter circuit:

This unit performs the same operation as household inverters. Inverter circuit converts switched DC power from a rectifier or backup batteries to again an AC output that powers the sensitive electronic gadgets.

The whole conversion process (from AC to DC and again DC to AC) and filtering smooth out events such as spikes, surges, and electrical noise impulses that is ensuring the final smooth, controlled, and regulated pure sine wave (AC power) to sensitive loads. In this way, Online UPS protects electronic gadgets.

Static switch:

Despite the all safety features, there is one possibility of failure is present. And that is the failure of UPS or uninterrupted power supply. In that scenario a static switch automatically connects the load to the mains supply, bypassing the rectifier, batteries, and inverter circuit.

Display panel:

The display panel represents the battery charging level, load status, and more details. In the initial days, these display panels were contained different color LEDs to display the backup battery power level, rectifier, and inverter circuit states. But as of now many Online UPS manufacturers are using LCD to display the state of the gadget. This unit has a single PCB that contains an LCD, pushbuttons, few IC’s and other components.

Cooling unit:

It contains several DC fans with a proper heat sink that sucks the hot air from the Online UPS and dissipates it into the outer atmosphere. We can say that it is a mini exhaust fan for this gadget. The cooling unit is an important part of Online UPS. If this unit does not perform its work efficiently then the overall performance or load handling capacity of online UPS gets reduced. Why? Can you guess? Yes! The heat generated by the solid-state components reduces their performance.

Backup batteries:

An Online UPS needs multiple batteries either in series, parallel, or both types of connection. These rechargeable batteries are specifically designed to work in the close and confined area. Backup batteries are generally made of Li-ion and these are having a high ampere-hour rating to provide long backup time to sensitive loads.

Backup batteries

Backup batteries

Working of Online UPS:

We can divide the working process of the Online UPS into the following steps:

  1. During abnormality or even in normal condition of main power supply, the inverter supplies energy from the mains through the rectified AC (DC power), which charges the backup batteries continuously.
  2. When the main power fails, the inverter still supplies energy to the loads by using the backup batteries.
  3. As per the result, there is no transition time between normal to store energy mode.
  4. In general Online UPS provides total independence between input and output voltage amplitude and frequency. So high output voltage quality can be achieved.
  5. When an overload occurs, the bypass switch connects the load directly to the mains supply, to provide a guarantee to the continuous power supply to the load.


Online UPS systems are ideally being used in environments with sensitive equipment like research laboratories, hospitals, security systems like Intruder alarm system, etc. It also stabilizes the voltage fluctuations as a Voltage stabilizer.

Thanks for reading. See you soon with another exploration!

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One Comment

  1. […] we know, power is required for every gadget. Most of the intruder alarm system worked with Online UPS that provide zero downtime to your entire security system. Most offices use backup power generators […]

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