ECO6907 Datasheet | Philips Semiconductors

APPLICATION NOTE Design of HF wideband power transformers ECO6907 w w w t a .D S a e h U 4 t e .c m o w w w .D a S a t e e h U 4 t m o .c Philips Semiconductors Design of HF wideband power transformers CONTENTS 1 2 3 3.1 3.2 4 4.1 4.2 5 5.1 5.2 6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.8.1 6.8.2 7 7.1 7.2 8 INTRODUCTION TRANSFORMER SPECIFICATION INFLUENCE OF THE CORE ON PERFORMANCE Primary Inductance Core Losses INFLUENCE OF THE TRANSMISSION LINE ON PERFORMANCE Resistive Loss and Power Handling Mismatch loss PENSATION TECHNIQUES pensation at Low Frequencies pensation at High Frequencies TRANSFORMER CONFIGURATION Phase Reversing Transformer Balanced to Unbalanced Transformer Symmetrical 1 : 4 Impedance Transformer Asymmetrical 1 : 4 Impedance Transformer Symmetrical 9 : 1 Impedance Transformer Asymmetrical 1 : 9 Impedance Transformer Single-ended Hybrid Push-pull Hybrid Impedance Step-up Type Impedance Step-Down Type PRACTICAL EXAMPLES 12.5 Ω Balanced to 50 Ω Unbalanced Transformer 50 Ω Unbalanced to 5.55 Ω Balanced Transformer REFERENCES Application Note ECO6907 1998 Mar 23 Philips Semiconductors Design of HF wideband power transformers 1 INTRODUCTION Application Note ECO6907 Transmission line power transformers can be used to perform a variety of functions, among which are phase reversal, balanced to unbalanced coupling, impedance transformation and hybrid functions. Such transformers find many applications in wide-band power amplifiers for both s.s.b. transmitters in the h.f. region and f.m. transmitters in the lower v.h.f. region. The properties of a practical h.f. power transformer are discussed here and their effect on transformer performance is analysed. Since losses must be kept low, in practice the transformer will use a ferrite core. Further, we have limited the discussion to cores without an air-gap since these have a low stray magnetic field, a high permeability, and can cover the power range (up to 80 W) dealt with here. Data...