17.7 Choke

17.7 Choke

It is a coil of thick copper wire wound closely in a large number of turns over a soft iron laminated core. A choke is often modeled as a series RL-circuit, consisting of a resistor $R$, having very small value of resistance, in series with an inductor $L$, of quite large inductance $X_{L} = 2\pi f L$, as shown in Fig. 17.7(e). The inductance $L$ of the choke coil is also very high due to the high permeability of iron core on which choke coil is wound. As the resistance $R$ of a choke coil is negligibly small, therefore, the power factor ($\cos\theta$) of the choke coil is almost zero. Thus, the phase difference $\theta$ between the current and voltage for a choke coil is nearly equal to $90^{\circ}$. So practically, no power is dissipated as heat by a choke coil. Also choke is used to block high frequency AC while allowing DC and low frequency AC to pass. Choke coils are used to filter out high frequency AC noise from electronic circuits, ensuring a cleaner DC output. They are essential in switch-mode power supplies, helping to regulate voltage and filter out switching noise. Choke coils prevent unwanted RF signals from leaking out of circuits, protecting other sensitive components. Chokes in fluorescent lights generate transient voltages across the tube, making it conducive to the breakdown voltage of the gas inside. Choke coils can limit the rate of current changes in circuits, preventing damage to insulation from sudden surges.

(Fig. 17.7(e): A choke)

Do you know?

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Why capacitor and inductor behaves differently for AC and DC? For DC supply, when $f = 0$, then $X_{L} = 2\pi fL = 0$, thus, inductor acts as conductor for DC For AC supply when $f = 0$ Then $X_{C} = 1/2\pi fC = 1/0 = \infty$ Thus, capacitor blocks DC but allows AC to pass through it.