| 摘要 |
<p>A transformer 10 comprises a primary winding 12 and secondary winding 14 disposed around a core 16. The primary and secondary windings have a different number of turns and are connected in series between the input 18 and output 20 phase terminals of the transformer. A switch means 44, 46, 48 is associated with the primary winding for selectively connecting or disconnecting it from the phase supply terminal. The core may be a toroidal core and may have a plurality of primary windings, each having a different number of turns. A control circuit is suitably provided for independently switching the or each primary winding into, or out of, the transformer. The control circuit may comprise a first switch 44 interposed between the primary winding and the input phase terminal, a second switch 46 in a shunt around the primary winding, a resistor 42 wired in series between the primary winding and the phase output terminal, and a third switch 48 in a shunt around the resistor.</p> |
