PCB transformers are used on print boards for electronics, control transformers with block terminals and control cabinets. High frequency transformers are used in power supplies.
Information about application for EI transformers can be found here.

Small transformers conform to EN 61558:

Types EI, M, PM, UI
Cut cores from 0,1 VA up to 5 kVA
Open and potted version for PCB or with block terminals
HF-transformers ETD, EE, EF, EFD, RM, PM for PCB or SMD from 0,1 VA up to 3000 VA and a frequency up to 500 kHz