In a transformer, what happens to the output current when the output voltage is lower than the input voltage?

In a transformer, when the output voltage is lower than the input voltage, the behavior of the output current is closely related to the principle of conservation of power and the relationship of voltage and current in transformer operation. A transformer operates on the principle that power (voltage multiplied by current) in the primary winding is equal to power in the secondary winding under ideal conditions, disregarding losses (which is a more complex discussion but illustrates a key point).

If the output voltage is reduced compared to the input voltage, the transformer adjusts to maintain the balance of power transfer. This means that for a given amount of power being delivered by the transformer, a decrease in output voltage will result in an increase in output current. This relationship is underscored by the transformer equations involving turns ratio and the properties of inductance.

In practical terms, if you draw more power from the transformer at the secondary side by lowering the voltage, the output current must increase proportionally to provide the same power level. For example, if the output voltage is halved, the output current must double to maintain power equivalence (ignoring losses), thereby demonstrating that a decrease in voltage allows for an increase in output current.

This principle is fundamental in understanding transformer operation, especially in applications where