11.1: Theory Overview

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The primary function of a rectifier is to turn an incoming AC waveform into a pulsating DC waveform. This can be achieved by simply blocking one of the two polarities from reaching the load. This is called a half-wave rectifier. A rectifier might be used as part of an AC to DC power supply but might also be used as part of a signal processing system. Ideally, a diode will behave as either an open or a closed switch depending on the polarity of the applied signal. This means that one polarity can be allowed through while the other can be blocked, perfect for this situation. In reality, the diode will require a forward turnon potential which results in a portion of the allowed signal being lost (e.g., the first 0.7 volts will be lost when using a silicon device). This fact makes a simple diode rectifier ineffective when used with very small signal amplitudes. Finally, in order to “fill the gap” where the blocked polarity would have been, a capacitor can be used to store some of the energy at the peak to be released during the gap. The higher the capacitance value, the more effective the smoothing will be.