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Numerous AC diode applications have been examined in this chapter. A single diode may be used to create half-wave rectification, producing pulsating DC from AC. This is achieved by simply blocking one of the two polarities with a diode. A more efficient form of rectification is full-wave rectification. In this scheme, one of the two polarities is effectively flipped. This may be achieved via a two diode circuit that employs a split secondary transformer or via a four diode bridge circuit using a non-tapped secondary. The addition of a split secondary to the bridge circuit enables a dual polarity output.
In order to smooth the pulsating DC into a relatively constant level, a filter capacitor is added in parallel with the load. The larger the capacitor, the greater the filtering and smoothing action, however, this will also increase peak charging current. A Zener diode may be employed to further stabilize the output voltage.
Clippers are used to limit the range of an input signal. They may be designed to clip the positive portion, the negative portion or both polarities of the input waveform. The positive and negative clip levels may be adjusted independently.
Clampers are used to create a DC level shift that is dependent on the peak level of the input waveform. The shift may be positive or negative, and may also include an optional bias. The operation of the clamper hinges upon the charge versus discharge time constants for a series capacitor and associated diode.
3.5.1: Review Questions
1. List the advantages and disadvantages of half-wave versus full-wave rectifiers.
2. Discuss the advantages and disadvantages of a full-wave bridge rectifier versus a two diode center-tapped rectifier.
3. What is the purpose of the capacitor in a rectifier/power supply circuit?
4. Under what load conditions will a Zener regulator fail to maintain regulation of the output voltage?
5. What is ripple? How might it be reduced?
6. What is the function of the DC source(s) in a biased clipper?
7. What is the function of the capacitor in a clamper circuit?