The following summarizes the major points made in Chapter 18.

1. The power supply of an electronic system is used to convert the ac energy provided by the wall outlet to dc energy.
   
   
2. There are two basic types of power supplies: linear and switching. Basic linear power supply circuits are the focus of this chapter.
   
   
3. A basic linear power supply consists of a transformer, a rectifier, a filter, and a voltage regulator. (See Figure 18.1.) The ac input is applied to the transformer. The rectifier is a diode circuit that converts ac to pulsating dc. The filter reduces the variations in the output voltage from the rectifier. The voltage regulator maintains a relatively constant output voltage from the power supply.
   
   
4. There are three types of rectifiers: the half-wave, full-wave, and bridge rectifiers.
   
   
5. A half-wave rectifier is simply a diode that is placed in series between a transformer and its load.
   
   
6. The diode in the half-wave rectifier eliminates either the negative or positive alternations of the transformer output. A positive half-wave rectifier eliminates the negative alternations of the transformer output. As a result, the rectifier output contains only positive alternations. A negative half-wave rectifier eliminates the positive alternations of the transformer output. As a result, the rectifier output contains only negative alternations.
   
   
7. The direction of the rectifier diode determines the output polarity for half-wave rectifiers. Positive and negative half-wave rectifiers are compared in Figure 18.6.
   
   
8. The average load voltage (V_ave) produced by a rectifier is the dc average of the circuit output pulses. V_ave is found as
   
   
9. The analysis of a half-wave rectifier is demonstrated in Example 18.2.
   
   
10. Peak inverse voltage (PIV) is the maximum amount of reverse bias that will be applied to a diode in a given circuit. For a half-wave rectifier, PIV = V_S(pk).
    
    
11. A full-wave rectifier produces a single-polarity output by converting negative alternations to positive alternations (or vice versa). A full-wave rectifier requires the use of a center-tapped transformer. The operation of a full-wave rectifier is illustrated in Figure 18.10. The analysis of a full-wave rectifier is demonstrated in Example 18.3.
    
    
12. The output polarity of a full-wave rectifier is determined by the direction of the diodes.
    
    
13. The PIV produced by a full-wave rectifier is approximately twice the peak load voltage. PIV = V_S(pk) – 0.7 V.
    
    
14. The bridge rectifier is a 4-diode full-wave rectifier. It is the most commonly used because it does not require the use of a center-tapped transformer. Using transformers with equal secondary voltages, it produces nearly twice the peak load voltage, average load voltage, and average load current of a full-wave center-tapped rectifier.
    
    
15. The bridge rectifier works on the principle of alternating the conduction of diode pairs. The operation of a bridge rectifier is illustrated in Figure 18.15. The analysis of a bridge rectifier is demonstrated in Example 18.4.
    
    
16. Figure 18.18 provides a comparison of half-wave, full-wave, and bridge rectifiers.
    
    
17. The output from a rectifier is normally connected to a filter. (See Figure 18.19.) A filter is a circuit that significantly reduces the variations in the pulsating dc output from the rectifier. The most commonly used filter is the capacitive filter.
    
    
18. The small change in voltage that remains in the output from a filter is referred to as ripple voltage (V_R).
    
    
19. A capacitive filter works on the principle of switching time constants. (See Figure 18.20.) The capacitor charges through the diode(s). The charge circuit has a short time constant. The capacitor discharges through the load. The discharge circuit has a long time constant.
    
    
20. A brief surge current is generated through a filtered rectifier when power is first applied to the circuit.
    
    
21. The greater the value of a filter capacitor, the greater the magnitude and duration of the surge current. Therefore, surge current places a practical limit on the value of any filter capacitor.
    
    
22. When a filter is connected to the output of a half-wave rectifier, the PIV applied to the rectifier diode doubles to 2V_S(pk).
    
    
23. Adding a filter to a full-wave or bridge rectifier does not affect the PIV applied to the rectifier diodes.
    
    
24. Surge current problems can be eliminated by using a filter that contains an inductor placed in series between the rectifier output and the load. (See Figure 18.27.)
    
    
25. LC filters provide the best overall protection from surge currents and excessive ripple but are the most expensive to use.
    
    
26. A clipper is a circuit used to eliminate a portion of an ac signal.
    
    
27. A series clipper contains a diode that is positioned in series between the source and the load. The circuit input passes through to the output when the diode is forward biased (conducting). When the diode is reverse biased by the input signal, it does not conduct. In this case, there is no voltage developed across the load.
    
    
28. A negative series clipper eliminates the negative portion of its input signal. A positive series clipper eliminates the positive portion of its input signal. (See Figure 18.29.)
    
    
29. A shunt clipper contains a diode that is in parallel with the load. When the diode is reverse biased (not conducting), the output waveform resembles the input waveform. When the diode is forward biased (conducting), the load is shorted. Therefore, the voltage across the load equals the drop across the diode.
    
    
30. Shunt clipper operation is illustrated in Figure 18.30. The series current-limiting resistor (R_S) is included to prevent the diode from shorting the signal source to ground when forward biased.
    
    
31. The analysis of a shunt clipper is demonstrated in Examples 18.6 and 18.7.
    
    
32. A biased clipper is a shunt clipper that uses a dc voltage source to bias the diode. This allows the circuit to clip the input at values other than the diode V_F.
    
    
33. A comparison of the various clipper circuits is provided in Figure 18.36.
    
    
34. Clippers are commonly used to protect a circuit from transients.
    
    
35. A transient is an abrupt current or voltage spike that has an extremely short duration. Transients can seriously damage any circuit not designed to handle them.
    
    
36. Several transient protection circuits are shown in Figure 18.37.
    
    
37. A clamper (or dc restorer) is a circuit used to change the dc reference of an ac signal.
    
    
38. A positive clamper shifts its entire input signal above a dc reference voltage.
    
    
39. A negative clamper shifts its entire input signal below a dc reference voltage.
    
    
40. Clamper input/output relationships are illustrated in Figure 18.38.
    
    
41. A clamper changes the peak and dc average values of its input waveform. However, it does not affect the waveform's rms and peak-to-peak values.
    
    
42. Clampers work on the principle of switching time constants. The capacitor charge time is extremely short when compared to the input cycle time. The capacitor discharge time is extremely long when compared to the input cycle time.
    
    
43. Clamper operation is illustrated in Figure 18.40.
    
    
44. Biased clampers allow us to shift a waveform above (or below) a dc reference other than the approximate value of 0 V.
    
    
45. Several biased clampers are shown in Figure 18.42.
    
    
46. Zener clampers use a zener diode in series with the pn-junction diode to establish a dc reference voltage (that is approximately equal to V_Z).
    
    
47. A voltage multiplier provides a dc output voltage that is some multiple of its peak input voltage.
    
    
48. A half-wave voltage doubler provides a dc output that is approximately twice its peak input voltage. The name is derived from the fact that the output capacitor is charged during one-half of the circuit input cycle.
    
    
49. The operation of a half-wave voltage doubler is illustrated in Figure 18.44.
    
    
50. A full-wave voltage doubler uses two capacitors to produce an output that is approximately twice its peak input voltage. The name is derived from the fact that the two series capacitors are charged during alternate half-cycles of the circuit input cycle.
    
    
51. The configuration of a full-wave voltage doubler allows a filter capacitor to be placed across the two series capacitors. This filter capacitor reduces the ripple in the circuit output.
    
    
52. Full-wave voltage doubler operation is illustrated in Figure 18.46.
    
    
53. A voltage tripler produces a dc output voltage that is approximately three times its peak input voltage. Voltage tripler operation is illustrated in Figure 18.47.
    
    
54. A voltage quadrupler produces a dc output voltage that is approximately four times its peak input voltage. A voltage quadrupler can be made using two half-wave voltage doublers as shown in Figure 18.48.

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