<P> One common kind of decoupling is to protect a powered circuit from signals in the power supply . Sometimes, for various reasons, a power supply supplies an AC signal superimposed on the DC power line . Such a signal is often undesirable in the powered circuit . A decoupling capacitor can prevent the powered circuit from seeing that signal, thus decoupling it from that aspect of the power supply circuit . </P> <P> To decouple a subcircuit from AC signals or voltage spikes on a power supply or other line, a bypass capacitor is often used . A bypass capacitor can shunt energy from those signals, or transients, past the subcircuit to be decoupled, right to the return path . For a power supply line, a bypass capacitor from the supply voltage line to the power supply return (neutral) would be used . </P> <P> High frequencies and transient currents can flow through a capacitor to circuit ground instead of to the harder path of the decoupled circuit, but DC cannot go through the capacitor and continues on to the decoupled circuit . </P> <P> Another kind of decoupling is stopping a portion of a circuit from being affected by switching that occurs in another portion of the circuit . Switching in subcircuit A may cause fluctuations in the power supply or other electrical lines, but you do not want subcircuit B, which has nothing to do with that switching, to be affected . A decoupling capacitor can decouple subcircuits A and B so that B doesn't see any effects of the switching . </P>

What is required in a circuit to have a capacitance load