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An RF choke (radio frequency choke) is a type of inductor, but it differs in its application, function, and design. An RF choke uses frequency selectivity to allow the passage of low-frequency DC signals while blocking high-frequency AC signals such as radio frequency. To do this, the RF choke has a high impedance over the range of frequencies it’s designed to suppress. 

 

A wide variety of industries use RF chokes, including telecommunications, aerospace, medical, utility, for use in computer systems, cables, and motor drives.

What Are RF Chokes Used For?

RF chokes are used for:

  • Dimming and pulsing
  • Microprocessor control
  • Functions in applications that use:
    • Line filtering
    • DC output filtering

RF chokes are used in:

  • Computer cables for:
    • Oil and gas control systems
    • Elevators and conveyors
    • Robotics equipment
    • Pumping equipment
    • HVAC equipment
  • USB cables
  • Machine tool drives
  • Variable frequency motor drives

 

The reasons to use RF chokes are to:

  • Protect insulation from damage caused by step rises in circuit current. 
  • Break down voltage to keep it from exceeding system voltages

How Are RF Chokes Made?

RF Chokes are normally made using iron powder or ferrite beads and a coil of insulated wires that are wound in complex patterns on a donut-shaped magnetic core. The reason for the complex winding is to reduce the choke’s self-capacitance.

 

Larger RF chokes have lower cutoff frequencies, while smaller chokes have higher cutoff frequencies. 

How Do You Choose an RF Choke?

It’s important to choose the correct RF choke for your use. Otherwise, DC signals won’t pass with minimal attenuation, and they won’t have enough capacitance to counteract the RF choke wiring’s high-frequency skin effect. 

 

To choose an appropriate RF choke:

 

  1. Ensure its DC current capability matches the required bias current.
  2. Select a sufficiently high inductance value.
  3. Select an impedance that is much larger than the load resistance.
  4. Decide the maximum allowable DC resistance (usually between 1 and 10 Ohms).
  5. Pick as small a package as your application can handle.
  6. Look for a low Q inductor.
  7. See that the core material is useable in the frequency range you need.

 

When you follow these steps, you’ll get an RF choke that meets your needs without altering behavior and impedances due to parasitic elements of applied power.

Where Do You Get RF Chokes?

If you need guidance on finding the right RF choke for your specific application, or if you need a custom-manufactured RF choke, Schott Magnetics can help.

 

Since 1951, we have specialized in the custom design and contract manufacturing of a wide range of high-quality components, including RF chokes. 

Contact the experts at Schott Magnetics to tap into our knowledge and experience to get exactly what you need.

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