Definition
A transformer in which the output (secondary) voltage is lower than the input (primary) voltage. This is achieved by having fewer turns of wire on the secondary winding than on the primary winding. The voltage decrease is accompanied by a corresponding increase in available current, so the total power remains essentially the same (minus small losses).
Plain English
An electrical device that takes a higher voltage in and gives a lower voltage out. The trade-off is that the lower-voltage side can supply more current.
Context Anchor
Seen in aircraft electrical system descriptions, power supplies, and maintenance discussions where one part of the system needs a lower voltage than another part provides.
Derivation
The name describes the action: it 'steps down' the voltage to a lower level. The opposite device is a step-up transformer.
Why Pilots Care
Ensures that sensitive avionics receive the correct lower voltage to operate safely without damage from higher aircraft system voltage.
Intuition Check
Do not read “step-down” as meaning the transformer reduces everything about the electricity. It lowers voltage; it does not create extra electrical power.
Example Sentence 1
The 26-volt instrument bus is fed through a step-down transformer from the aircraft's 115-volt AC system.
Example Sentence 2
Mechanics test the step-down transformer to confirm it delivers steady reduced voltage to the cockpit displays.