Question 5.6: Briefly describe the circuit action for each of the circuits...

Figure 5-9a shows how zener diodes and ordinary silicon diodes can produce several dc output voltages given a 20-V power supply. The bottom diode produces an output of 10 V. Each silicon diode is forward biased, producing outputs of 10.7 V and 11.4 V, as shown. The top diode has a breakdown voltage of 2.4 V, giving an output of 13.8 V. With
other combinations of zener and silicon diodes, a circuit like this can produce different dc output voltages. If you try to connect a 6-V relay to a 12-V system, you will probably damage the relay. It is necessary to drop some of the voltage. Figure 5-9b shows one way to do this. By connecting a 5.6-V zener diode in series with the relay, only 6.4 V appears across the relay, which is usually within the tolerance of the relay’s voltage rating. Large electrolytic capacitors often have small voltage ratings. For instance, an electrolytic capacitor of 1000 µF may have a voltage rating of only 6 V. This means that the maximum voltage across the capacitor should be less than 6 V. Figure 5-9c shows a workaround solution in which a 6-V electrolytic capacitor is used with a 12-V power supply. Again, the idea is to use a zener diode to drop some of the voltage. In this case, the zener diode drops 6.8 V, leaving only 5.2 V across the capacitor. This way, the electrolytic capacitor can filter the power supply and still remain with its voltage rating.