Low-Pass RL Filter
A circuit of Low-Pass RL Filter is shown in Figure (A). Here, coil offers high reactance to high frequencies and low reactance to low frequencies.
Hence, low frequencies up to fc can pass through the coil without much opposition. The output voltage is developed across R.
Figure (B) shows the frequency output response curve of the filter. As seen at fc,
V0 = 0.707 Vi
and its attenuation level is –3 dB with respect to V0 i.e. the voltage at f = 0.
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However, it may be noted that being an RL circuit, the impedance phase angle is +45° (and not –45° as in low-pass RC filter). Again at fc, R = XL.
Using the voltage-divider rule, the output voltage developed across R is given by
Read article – low-pass RC filter
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