RL Circuit - Parallel Circuit

Parallel Circuit

The parallel RL circuit is generally of less interest than the series circuit unless fed by a current source. This is largely because the output voltage is equal to the input voltage —as a result, this circuit does not act as a filter for a voltage input signal.

With complex impedances:

\begin{align} I_R &= \frac{V_{in}}{R} \\ I_L &= \frac{V_{in}}{j\omega L} = -\frac{jV_{in}}{\omega L} \end{align}

This shows that the inductor lags the resistor (and source) current by 90°.

The parallel circuit is seen on the output of many amplifier circuits, and is used to isolate the amplifier from capacitive loading effects at high frequencies. Because of the phase shift introduced by capacitance, some amplifiers become unstable at very high frequencies, and tend to oscillate. This affects sound quality and component life (especially the transistors), and is to be avoided.

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