Energy passes through a changing magnetic field.
A transformer has windings linked by magnetic flux, usually guided by a core. An alternating voltage on the primary winding produces changing flux that induces a voltage in the secondary.
An ordinary transformer needs changing flux for sustained operation. It is not a device for converting steady DC directly to a different DC voltage.
Follow the energy transfer.
- Primary windingReceives the AC supply.
- Magnetic coreLinks the windings through changing flux.
- Secondary windingSupplies the connected load.
The turns ratio sets the ideal voltage ratio.
With ten times as many primary turns as secondary turns, 240 V AC on the primary gives 24 V AC on the secondary.
The relationship is V₂ ÷ V₁ = N₂ ÷ N₁. Increasing the number of secondary turns relative to primary turns increases the secondary voltage. The frequency stays the same.
Changing voltage does not create power.
In the ideal model, input and output power are equal. Reducing voltage allows a corresponding increase in current capability for the same power, subject to the transformer’s rating. Real transformers have losses and heat up.
A transformer’s VA rating and its voltage ratings describe different limits. A correct voltage ratio alone does not establish suitability for a load.
Where a transformer fits in a lift.
Transformers may supply control or auxiliary circuits, especially in older equipment. A transformer output is still AC; rectification is a separate function when DC is needed.
Modern electronic supplies may contain a transformer operating at a much higher frequency than the incoming mains. That is still induction, used within a larger conversion circuit.
A closer look
An autotransformer has a shared winding and does not provide galvanic isolation between its input and output. Even a separate-winding transformer must have the appropriate construction and ratings for its intended isolation duty.
Check your understanding
Does stepping 240 V AC down to 24 V AC also turn it into DC?
Reveal the explanation
No. A transformer changes the AC voltage level. A rectifier is needed to convert AC to DC.