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| SEC. 24-1 SUPPLY
CHARACTERISTICS Load regulation indicates how much the output voltage changes when the load current changes. Line regulation indicates how much the load voltage changes when the line voltage changes. The output resistance determines the load regulation. SEC. 24-2 SHUNT REGULATORS The zener regulator is the simplest example of a shunt regulator. By adding transistors and an op amp, we can build a shunt regulator that has excellent line and load regulation. The main disadvantage of a shunt regulator is its low efficiency, caused by power losses in the series resistor and shunt transistor. SEC. 24-3 SERIES REGULATORS By using a pass transistor instead of a series resistor, we can build series regulators with higher efficiencies than shunt regulators. The zener follower is the simplest example of a series regulator. By adding transistors and an op amp, we can build series regulators with excellent line and load regulation, plus current limiting. SEC. 24-4 MONOLITHIC LINEAR REGULATORS IC voltage regulators have one of the following voltages: fixed positive, fixed negative, or adjustable. IC regulators are also classified as standard, low-power, and low-dropout. The LM78XX series is a standard line of fixed regulators with output voltages from 5 to 24 V. SEC. 24-5 CURRENT BOOSTERS To increase the regulated load current of an IC regulator such as a 78XX device, we can use an outboard transistor to carry most of the current above 1 A. By adding another transistor, we can have shortcircuit protection. SEC. 24-6 DC-TO-DC CONVERTERS When we want to convert an input dc voltage to an output dc voltage of another value, a dc-to-dc converter is useful. Unregulated dc-to-dc converters have an oscillator whose output voltage is proportional to the input voltage. Typically, a push-pull arrangement of transistors and a transformer can step this voltage up or down. Then, it is rectified and filtered to get an output voltage different from the input voltage. SEC. 24-7 SWITCHING REGULATORS A switching regulator is a dc-to-dc converter that uses pulse-width modulation to regulate the output voltage. By switching the pass transistor on and off, the switching regulator can attain efficiencies from 70 to 95 percent. The basic topologies are the buck (stepdown), boost (step-up), and buck-boost (inverting). This type of regulator is very popular in computer and portable electronic systems. |