use of broadband transformers

1. CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
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“CONSTRUCTION AND USE OF
BROADBAND TRANSFORMERS”
Under the guidance of :
Mr. Debashis Jena

2. CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
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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

3. CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
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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

4. Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
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5. CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
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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

6. CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
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Typical characteristic curve of Insertion loss Vs Frequency

7. CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
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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

8. CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
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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

9. CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
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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

10. CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
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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

11. Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
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12. Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
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13. CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
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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.

14. CONSTRUCTION AND USE OF BROADBAND TRANSFORMERS
Technical Seminar Presentation 2004 N. SAI KIRAN KUMAR EE200118248
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THANK YOU