Control transformers (STU)

AEE produces control transformers, also referred to as STU-trafo, ranging from 40VA to 1600VA. The fully custom-made control transformers can be manufactured in single pieces, small runs but also in series, completely according to your specifications. Installation in a cabinet or panel integration is also possible.


A control transformer is a transformer with separate windings that supplies power for an auxiliary power chain. To power the auxiliary power chain, a control transformer is often connected between two phases of a three-phase network. The transformer allows a differing voltage in the auxiliary power chain for electronic components. The design of these transformers is in accordance with EN 61558-2-2. Our control transformers are also available with UL certification (see UL transformers for the specifications)



The control transformers are single phase with separate windings, standard 50/60 Hz, insulation class E and suitable for an ambient temperature of up to 45°C. AEE also supplies designs with a primary voltage of 400V and 690V.


All control transformers are available with a Lloyds quality mark.


Properties of the control transformers:

  • Single-phase transformers with separate windings
  • Standard frequency 50/60Hz
  • Air-cooled
  • Insulation class E
  • Protection class IP00
  • Version type, from EI60 to EI192 long side
  • Designed with touch-safe terminals
  • Reliable and long service life


Control transformers can easily be overloaded briefly by 10-15%.