A larger inductor can also be used to remove more of an AC signal, which can be useful when trying to attenuate low frequencies. However, all AC frequencies are attenuated by some degree so that the ratio of the DC component of the output to the AC component can be significantly improved even though some AC signal is still allowed to pass. This means that higher frequencies are attenuated more highly by the inductor lower frequencies are attenuated less. Inductive reactance (XL) is measured in Ohms, and is proportional to the frequency of the AC signal as well as the inductance of the inductor: Inductor filters operate based on the principle of inductive reactance, which is the opposition to an AC current by an inductor. The L-filter then improves the output of the bridge rectifier by using an inductor to smooth out the waveform. The bridge rectifier produces a pulsed DC signal the negative half-cycles of the sine wave from the transformer are inverted so that the current only travels in one direction. The transformer (XFMR1) reduces the voltage of the signal to the desired level. The signal goes through multiple changes as it passes through the circuit:

This complete circuit includes an AC source input, step-down transformer, diode bridge rectifier circuit, inductor filter, and a resistive load. Inductor Filter (L-Filter) Circuit Diagram The inductor introduces impedance to the flow of AC called inductive reactance. The AC component, however, is impacted significantly by the inductor. The DC component is allowed to flow like a short circuit, without any attenuation by the inductor. Since inductors operate by opposing any change in voltage, the inductor will only oppose the AC component of the rectifier’s output.

Any voltage that is dropped across the inductor will therefore not be measured by the load (V out). This means that the output signal passes directly through the inductor.

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Bridge rectifier pi filter design