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Mains Voltage Power Transformers

Battery Eliminators, Power Packs and Mains Adapters etc. are names given to products that are made to provide a DC supply from the Mains Supply. Even in Equipment like a computer or radio a power supply block is required. Step down 50/60 Hz transformers are used to give isolation from mains and to obtain a lower voltage. SMPS designs are more popular as can give more power in a smaller size and dont heat up.

Amplimo - Toroidal Transformers

 Mains Power Packs with 50Hz Transformers are still popular for audio and some product safety sensitive applications, as they are more isolated, reliable and EMI-RFI  free. 

Power Supplies Section  - ideas on how Transformers are used in making Power Supplies and Battery Chargers.

Low Frequency Power Transformers are used to step down mains voltage of 230V or 110V to safer voltages like 12V and 6V. The core is made of laminations of a Conditioned Alloy of Iron. The windings are Enameled or Insulated Copper Wire. They provide both Isolation and Safety while Scaling the Voltage and Power.

In Switch Mode Power Supplies the Transformers and Cores are High Frequency Coils Transformers in SMPS.

Transformer with Primary and
                      Secondary Windings

Series and Parallel Connections in transformers.

Observe the Dot-Polarity. When windings are in parallel the current capacity doubles. When windings are in series the voltage doubles. (or adds up).

Wrong dot polarity in series connection just cancels the voltage and a small residual imbalance voltage remains. If wrong polarity connection is done in parallel, then a short circuit or overload may occur.

Hysteresis - Charles Proteus Steinmetz - See how he made the Hot Transformers and Motors Run Cool!.

Mains Adapter 230V AC 50 Hz to Rectified DC -  How is a small power transformer used to get DC.

                        and Parallel transformers
Center Tap Transformer

This is when you need to build a symmetrical dual supply like +12V and -12V supply for an opamp design. This is also good for a two diode full wave rectifier. But when you make a dual supply use a bridge and the center tap is ground.

CWS - Magnetics Coils Inductors Transformers

If you use just two diodes then one winding may be loaded more than other. That may not be good for long term transformer life. The core may get magnetized.

A more accurate reference on transformers is  ... Basic Hook Up Data on Transformers from Hammond

Center Tap Transformer

Types of Transformers

Classic Transformer


  • Split bobbin assures product safety
  • Easy Cabinet or Panel mount
  • Wires for connection-termination
  • Mechanically Sturdy, use 'lock nuts'

Terminals Transformer

Terminals Transformer

  • Easy replace on service.
  • Panel-Cabinet Mount.
  • Clamp Serves as Shield.
  • Split Bobbin Insulation.


PCB Transformer

  • Mount on PCB and Solder.
  • More Reliability, no-wires.
  • Winding slip not possible.
  • Make Modular supply card.


Toroidal Transformer

  • High Efficiency
  • Low Heat inside box
  • Low Profile and space
  • Long Life and low EMI

Transformers Made by Hammond Manufacturing