Power transformer » Transformer Articles »What differentiates a switch mode power transformer and a power transformer from other transformers?

What differentiates a switch mode power transformer and a power transformer from other transformers?

Power transformers are essentially A.C (alternating current) devices. They cannot support transformer operation from a fixed D.C. (direct current) voltage source. But they can support transformer operation in transient conditions that permits reversal or resetting of the transformer’s magnetic flux levels.

Switch mode power transformers are called so due to their switching action needed to sustain transformer operation. Switch mode power transformers are used in electronic applications, typically within a switch mode power supply. Switch mode power transformers may have several secondary windings. A switch mode power supply is usually operated from a D.C. source like battery to convert the input D.C. to other output D.C. sources. In the switch mode power transformer, you can control the amount of power delivered to the load circuit of the transformer by controlling the amount of “on time” and “off time” of the switches. Switch mode power transformer features low wastage, high output power, low temperature rise and wide range of working frequency.

The design of switch mode power transformer differs based on the type of circuit used. The three main circuit configurations of switch mode power supply are Buck, Boost, and Flyback. Buck circuit is also called as inverter, D.C. converter, forward converter, or feed forward. The switch mode power transformer used in the Buck Circuit couples energy from the primary side to the secondary side. Buck circuit switch mode power transformer couples energy without storing it. Hence Buck circuit switch mode power transformer acts an ideal transformer. Flyback and boost circuit switch mode power transformers deliberately store energy during the “on time” or charging cycle and then discharge energy during the “off time” or discharging cycle. As the Flyback and boost circuit switch mode power transformers intentionally store energy, the Flyback circuit switch mode power transformers and boost circuit switch mode power transformers do not function as ideal transformers.

Switch mode power transformers are available in a wide variety of shapes and sizes. They ate used for Buck, Flyback, and Boost circuit configuration switch mode power supplies. The different shapes of switch mode power transformer are almost similar to that of an ideal transformer. The different shapes include “core with bobbin” structures and toroids. The “core with bobbin” structures include E core, EI core, EE core, EP core, ER core, ETD core, ERL core, EFD core, RM core, PQ core, POT core, U core, etc.

EI and EE core type switch mode power transformers are used widely. EI and EE core type switch mode power transformers features high working frequency, wide range of working voltages, high output power, and good thermal stability. These types of switch mode power transformers are used in LCD power supply, program controlled switchboard, large power UPS inversion power supply, PC power supply and power supplies of small electronic equipments.

The ER, ETD and ERL core type switch mode power transformers features high output power, low wastage, wide range of working frequency, low temperature rise and stable performance. They are used in color TV power supply, PC switching power supply, program controlled switch board, display unit power supply, DVD power supply and precision equipment power supply.

RM, EP, PQ and EFD core type switch power transformers features low magnetic leakage, low wastage and low distribute capacitance. They are used in program controlled switchboard, facsimile machine, etc.