construction and use of broadband transformers 1

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N. SAI KIRAN KUMAR EE200118248

CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS

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“CONSTRUCTION AND USE OF

BROADBAND TRANSFORMERS”

Under the guidance of :

Mr. Debashis Jena

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I INTRODUCTION

• Wound magnetic devices that are designed to transfer energy over a wide frequency range

• Most broadband transformers are wound on ferrite toroids or rods

• Used in telecomm equipment

• Balun or binocular cores are used for broadband transformers that must accommodate RF power

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TYPES

Two types:

Conventional type and transmission-line type

Conventional type

Permits to obtain any transformation ratio we need

Transmission-line

With twisted or parallel windings and produce specific integers of impedance transformation, such as 4:1, 9:1 and 16:1

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Determining- the -Minimum- Number - of - Turns

Square root of the impedance ratio

Primary reactance is usually around 5 times the primary impedance

With a 200 ohms to 50 ohm transformer, we would allow a reactance of 1,000 ohms, required inductance of around 88 uH

Turns = 1,000 X SQRT (L in mH / AL factor)

= 1,000 X SQRT (0.088 / 68) = 36 turns

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Typical characteristic curve of Insertion loss Vs Frequency

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TRANSFORMERS ON BALUN CORES

Balun cores are made from ferrite.

The permeability of the material core is s 850 to 900 for applications from 1.8 to 30 MHz.

Are created by using two rows of ferrite toroids, side by side

Cores are glued together by means of quick setting epoxy cement to form two separate tubes of toroids

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Examples of broadband RF Transformers. The low Z-winding is generally a single, U-shaped turn of wire.The larger winding has as many turns as are needed to provide the desired impedance transformation

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FREQUENCY BASED BROADBAND TRANSFORMERS

Low and Medium Frequency

Manganese zinc ferrites, such as Fair-Rite 77 or 78 materials, are very suitable

Core geometry should be such as to minimize the Rdc/L ratio

Parameter that is most critical is the shunt reactance (ωL)

High Frequency

Uses nickel zinc ferrites as the preferred core material

Band pass lies wholly above 500 kHz

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USES OF BROADBAND-TRANSFORMER

Used at the output of an active mixer

For matching a 50-ohm antenna to a grounded gate RF amplifier in a receiver or converter

Applied in push-pull RF power amplifier that uses two broadband transformers

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CONCLUSION

Can be designed to provide dc isolation, impedance matching and specific current or voltage ratios

Balun transformers are used in test equipment, mixers, receivers, transmitters and antenna circuits

Coverage from 1.8 to 30 MHz.

Efficiencies in the high 90% range.

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THANK YOU!!!

construction and use of broadband transformers 1

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