What is Transformer Rectifier and Its Applications

In the year 1958, electronics & crane aerospace have led the way to consistent aircraft AC to DC power conversion development. The TRUs (Transformer Rectifier Units) supply an efficient, affordable, as well as consistent power change while meeting at present the latest rigid power quality necessities. Worldwide, when the leading supplier of transformer rectifier units & auto-transformer rectifiers used for commercial aircraft. They offer field-proven, extremely consistent solutions that range from 125 to 250 amps.

What is a Transformer Rectifier?

A transformer rectifier definition is a transformer that contains thyristors otherwise diodes within the same tank and also includes voltage regulation. These transformers are used for the industrial process. This process can be done b using a significant DC supply. The industrial process using transformer rectifiers mainly includes electrolysis, dc traction, large variable-speed drive trains, smelting operations, etc. The application of this transformer rectifier will drive the design considerations which include the following.

  • Thyristors use the connection like bridge-type used for higher voltages
  • The interphase connection is used for applications like low-voltage and high current
  • Number of pulses (6, 12 and higher with phase-shifting)
  • Harmonic issues and eddy current.

Voltage regulation can be attained through on-load tap otherwise no-load changers on the high voltage region. Fine levels of this regulation can be obtained with the help of saturable reactors in the secondary region. The units of regulation can be fixed otherwise separate.

Most Important Features

The features of the transformer rectifier include the following.

  • Oil and air-cooled
  • Different kinds of controls like Manual – Variac or Tap control, constant current, current-voltage, auto reference as well as selection control.
  • Controlling of solar power
  • Current interrupter using GPS interface
  • SCADA for remotely controlling and monitoring
  • Remote Monitoring via GSM data logger
  • Data logger
  • Remote controlling and monitoring via PLC
  • Time Totalizer or Hours Run Meter
  • O/p current is 10A to 400 A
  • O/p voltage is 28 V DC
  • Rectification of 12 pulses otherwise 24 pulse
  • Field-proven and long life fan
  • Un-regulated designs for reliability & simplicity
  • Harmonic distortion is low with hygienic input power

Transformer Rectifier Working Principle

A TRU or transformer rectifier unit unites both the transformer & rectifier functions into a single unit. The main function of TRU is to convert AC to DC. This conversion is known as rectification. The different forms of TRU mainly include selenium oxide, mercury arc valves, silicon-based and semiconductor diodes.

Apart from altering alternate current to direct current, this current is used as the power source. These rectifiers detect flames & radio signals & flames. In addition, these can be used in a wide range of applications like providing power to radios, TVs, computers & other devices which need a stable DC supply.


Furthermore, these rectifiers provide the extremely polarized voltage which is required for welding. In such conditions, the supply is essential to control the output current of the circuit. This is accomplished by restoring the diodes using a bridge rectifier which can carry output voltage that can be controlled through switches.

Rectifiers are extremely helpful in industries that need high current. Therefore, machinists should be sure to utilize the right type of rectifier within their exact setting.

Transformer Rectifier Unit Circuit Diagram

A TRU is used to change AC to smooth DC. The circuit diagram of the transformer rectifier which is used within the battery charger of a car is shown below.

This TRU device uses 240 VAC & changes it into around 14 VDC for the battery charging. This process can be attained through a transformer. At first, it step-downs the voltage from AC to a reasonable stage and after that converts it through an assembly of a bridge rectifier into DC.


Most huge AC generator systems of aircraft contain committed transformer rectifier units, which function on a similar principle, even though they are somewhat extra complicated.

The TRU that is fixed to an aircraft can be normally supplied by 115 V 400 Hz 3-phase AC, and it is stepped-down via a 3-phase star-star wound transformer converts into 28 VDC using an assembly of the six-rectifier bridge. After that, the TRU’s o/p is fed to the DC bus bars of aircraft.

The basic protections of each TRU mainly include overheat and reverse current.

Different Types

The classification of TRU (transformer rectifier unit) can be done based on the input and output supply. They are

AC Operated TRU

The input supply of AC operated TRU is three-phase otherwise single-phase, whereas the output supply is up to 100 V DC & 1200 Amps DC.

DC Operated CPPSM Unit

The input supply of DC Operated CPPSM Unit is up to 48V DC, whereas the output supply is up to up to 50 V DC & 50 Amps DC.

AC / DC Operated Rectifier Unit

The input supply of AC / DC Operated Rectifier Unit is a single phase or 3- phase AC supply otherwise up to 48 V DC supply, whereas the output supply is up to 50 V DC & 50 Amps DC.

Hazardous Area Application

The input supply of hazardous area application is a single phase or 3- phase otherwise up to 48 V DC supply, whereas the output supply is up to 100 V DC and 100 Amps DC.


The transformer rectifier applications mainly include the following

  • Aircraft DC Bus Power
  • Business aircraft
  • Helicopters used for commercial purpose
  • Local & business jets
  • Aircraft used in military

Thus, this is all about the transformer rectifier unit. From the above information finally, we can conclude that these are used in aircraft buses, commercial aircraft, military transport, used in the military for trainers and fighters, etc. Here is a question for you, what is a half-wave rectifier transformer?