What Is a Choke?
A choke, as the name suggests, is an inductor that "chokes" (blocks) unwanted high frequency or the AC component, while readily passing DC.
How Does It Work?
A coil shows low resistance to DC, but as frequency rises its reactance (resistance) grows. This lets the DC component on the supply line pass while the high-frequency noise riding on it is suppressed.
Its Relationship to the Coil
A choke is really a coil used for a specific purpose (blocking noise/AC). "Coil" is the general term, while "choke" emphasizes the function. In power stages it's usually chosen with high inductance and high current.
| Type | Job |
|---|---|
| Power choke | Filtering the supply DC |
| RF choke (RFC) | Isolating RF from the supply line |
| Common-mode choke | Blocking common noise on two lines |
Difference From a Ferrite Bead
A ferrite bead turns noise into heat and damps it and is very small; a choke, as a real inductor, blocks over a wider frequency range and at higher current.
Where Is It Used?
Power-supply input/output filters, RF supply lines, audio amplifiers and EMI-reduction circuits.
Common Mistakes
- Current rating: in a power choke, if the saturation current is exceeded the filtering breaks down.
- Wrong type: a choke not designed for RF is ineffective at high frequency.
- Resonance: an unwanted resonance can form with the filter capacitor.
Frequently Asked Questions
Is a choke the same as a normal coil?+
What is an RFC?+
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