High Frequency Transformers (Audio Frequency Transformer and Intermediate Frequency Transformer)

(1) Audio Frequency (AF) Transformer

• Audio frequency range is 20 Hz to 20 kHz
• These transformers are especially designed for connecting different telephone systems to each other keeping their respective power supplies ‘isolated’.

Following are the functions of Audio Frequency (AF) transformer

1. To block DC component of an audio signal.
2. To provide impedance maching
3. To block Radio Frequency (RF) interference
4. To split or combine audio singals
5. Can be used as driving transformers

Uses of Audio Frequency (AF)

1. Use of RF transformer for impedance matching or as driver transformer.
2. Connecting different telephone systems
3. Used for changing voltage with little or no distortion of wave forms for isolating DC in one circuit from another for changing impedances of loads and for reversing phases etc.
4. AF transformers are used in Radio TV receivers
5. In music systems
6. In mixing consoles
7. In professional audio systems
8. In impedance matching

(2) Intermediate Frequency (IF) Transformer

• Transformers used for radio receivers , amplifiers , TV receivers are IF transformers.
• By connecting capacitors across both the windings these are tuned.
• Cores used – Ferrite cores.
• Advantage of Ferrite cores- Low hysteresis loss, and high permeability ; low eddy current loss.
• How ferrite core is made? – Ferrite is a powder metallic alloy with grains of ferrous metal compressed and held together by an insulating binder forms a core.
• This ferrite material is of F_e3O₄ ferric oxide combined chemically with zinc or manganese or nickel.
• If transfer is shown by a sketch and schematic diagram as in figure.

• Both windings are turned to the same frequency for tunning a screw is provided.