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Complete Electronics Self-Teaching Guide with Projects by Harry Kybett, Earl Boyson

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Diodes in AC Circuits Produce Pulsating DC

1 You can use diodes for several purposes in AC circuits, where their characteristic of conducting in only one direction is useful.

Questions
Assume that you apply + 20 volts DC at point A of the circuit, as shown in Figure 11.1.
A. What is the output voltage at point B? _____
B. Suppose that you now apply + 10 volts DC at point B. What is the voltage at point A? _____
Answers
A. 20 volts DC (Ignore, for now, the voltage drop of 0.7 volt across the diode.)
B. 0 volts (The diode is reverse-biased.)

2 Figure 11.2 shows the circuit in Figure 11.1 with a 20 Vpp AC input signal centered at + 20 volts DC.

Questions
A. What are the positive and negative peak voltages of the input signal? _____
B. What is the output waveform of this circuit? _____
Answers
A. Positive peak voltage is 20 volts + 10 volts = 30 volts. Negative peak voltage is 20 volts − 10 volts = 10 volts.
B. The diode is always forward-biased, so it always conducts. Thus, the output waveform is exactly the same as the input waveform.

3 Figure 11.3 shows a circuit with 20 Vpp AC input signal centered at 0 volts DC.

Questions
A. What are the positive and negative peak voltages of the input signal? _____ ...

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