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What is the working principle of transformer? How does the transformer change the voltage?
2019-03-14 14:17:06


I. Working Principle of Transformer

The following diagram is a schematic diagram of the transformer. In the diagram, the left side is the primary winding and the right side is the secondary winding. Both primary and secondary windings are wound on the core.

The transformer can only input AC voltage. AC voltage is input from both ends of primary winding of transformer and output from secondary winding.

After the AC voltage is input to the primary winding, AC passes through the primary winding, which generates alternating magnetic field. The magnetic field lines of the primary winding mostly consist of iron cores.

Because the secondary winding is also wound on the iron core or magnetic core, the variable magnetic force line passes through the secondary winding and generates induced electromotive force at both ends of the secondary winding. The voltage produced by the secondary winding is different from the input voltage (if the transformer is 1:1, the voltage is the same), and its frequency and variation law are the same as the input AC voltage.

This is the basic principle of transformer: according to the principle of electromagnetic induction, when a conductive object is in a changing magnetic field, it can induce current in the conductive body.

2. How to Change Voltage of Transformer

There is a special parameter for transformer to change voltage: voltage ratio.

The ratio of transformer to voltage represents the relationship between the number of turns of primary winding and the number of turns of secondary winding. From the transformer ratio, we can see whether a transformer is a step-up transformer or a step-down transformer, or a 1:1 transformer.

Voltage ratio = primary winding turns / secondary winding turns.

Voltage ratio less than 1 is a boost transformer, indicating that the number of primary winding turns is less than that of secondary winding turns.

Voltage ratio greater than 1 is a step-down transformer, which indicates that the number of primary winding turns is greater than that of secondary winding turns.

According to the working principle of transformer, current flows in from primary winding and out from secondary winding. Because the current direction of the input AC is constantly changing, there will be a magnetic field that changes synchronously with the current. Because the size and direction of the magnetic field are constantly changing, the current is induced in the secondary coil. Because the voltage on each coil is equal, the more coils the secondary coil has, the higher the output voltage from the secondary coil.

If the primary coil has more coils than the secondary coil, the voltage on the secondary coil will be reduced, which is a step-down transformer. Conversely, if the primary coil has fewer coils than the secondary coil, the voltage on the secondary coil will rise, which is a step-up transformer.