Voltage regulation

Chapter Voltage regulation

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • If a supply must have a minimum of ripple, two or three capacitor/choke pairsmight be cascaded, or connected one after the other (Fig. 21-11). Each pair is called asection. Multisection filters can consist of either capacitor-input or choke-input sec-tions, but the two types are never mixed.392 Power supplies21-11Two choke-input filter sections in cascade.Voltage regulationA full-wave rectifier, followed by a choke-input filter, offers fairly stable voltage undervarying load conditions. But voltage regulator circuitry is needed for electronic de-vices that are finicky about the voltage they get.Zener diodesYou learned about Zener diodes in the last chapter. If a reverse-biased Zener diode isconnected across the output of a power supply, as shown back in Fig. 20-7, the diodewill limit the output voltage of the supply by “brute force” as long as it has a high enoughpower rating.Zener/transistor regulationA Zener-diode voltage regulator is not very efficient if the load is heavy. When a supplymust deliver high current, a power transistor is used along with the Zener diode to ob-tain regulation (Fig. 21-12). This greatly reduces the strain on the Zener diode, so thata lower-power (and therefore less costly) diode can be used.Integrated circuitsIn recent years, voltage regulators have become available in integrated-circuit (IC)form. You just connect the IC, perhaps along with some external components, at theoutput of the filter. This method provides the best possible regulation at low and mod-erate voltages. Even if the output current changes from zero to maximum, the outputvoltage stays exactly the same, for all practical purposes.Regulator tubesOccasionally, you’ll find a power supply that uses a gas-filled tube, rather than solid-statecomponents, to obtain regulation. The tube acts something like a very-high-power Zener