Rectification and Filtering

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Rectification and Filtering:
In earlier sections, we discussed diodes, capacitors and transformers. In this section we will show how they are used together to convert A.C. to D.C.

Rectification:
In the diagram below, the two diodes are connected so that they only allow the positive pulses through to the capacitor. You should notice that the output at point 'A' is inverted with respect to output 'B'. When we have a center tapped transformer as above, the output is considerably smoother than when the there is only one secondary output (output 'B' wouldn't exist). The combined output is pulsed D.C. It is not A.C. because the voltage doesn't cross the reference (black dashed) line. In this circuit, the solid black circuit line would be the reference point and would be considered to be 'ground' (in reality, it would be connected to ground).

Filtering:
In the flash demo below, along the bottom you can see the AC waveform, the pulsed DC and two 'filtered' output diagrams. The left filtered diagram shows the effects of the smaller (lower value) capacitor. The rightmost filtered diagram shows the effects of the larger capacitor. The capacitors serve to fill in the gaps between the pulsed DC to provide a smoothed DC output. When you use the buttons below the diagrams, the current flow from the output of the power supply will increase or decrease (depending on the direction of the arrow on the button). When the current flow increases, the ripple increases. Notice how the ripple (roughness) with the larger capacitor is less significant at maximum current draw. When you put a load on a DC power supply (that's derived from an AC source), this ripple shows up on the supply. The severity of the ripple depends on the transformer's output capability, the size of the capacitor and the DC current being drawn from the supply.

Please note that, in the real world, the capacitors would work together to act as one larger capacitor. The ripple would be the same at all points after the diodes. The ripple as shown above is as if each capacitor was connected to the circuit independently.

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