4-38 The schematic drawing in view A is that of a shunt-type regulator. It is called a shunt-type regulator because the regulating device is connected in parallel with the load resistance. The schematic drawing in view B is that of a series regulator. It is called a series regulator because the regulating device is connected in series with the load resistance. Figure 4-32 illustrates the principle of series voltage regulation. As you study the figure, notice that the regulator is in series with the load resistance (R_{L}) and that the fixed resistor (R_{S}) is in series with the load resistance. Figure 4-32.—Series voltage regulator. You already know the voltage drop across a fixed resistor remains constant unless the current flowing through it varies (increases or decreases). In a shunt regulator, as shown in figure 4-33, output voltage regulation is determined by the current through the parallel resistance of the regulating device (R_{V}), the load resistance (R_{L}), and the series resistor (R_{S}). For now, assume that the circuit is operating under normal conditions, that the input is 120 volts dc, and that the desired regulated output is 100 volts dc. For a 100-volt output to be maintained, 20 volts must be dropped across the series resistor (R_{S}). If you assume that the value of R_{S} is 2 ohms, you must have 10 amperes of current through R_{V} and R_{L}. (Remember: E = IR.) If the values of the resistance of RVand R_{L} are equal, 5 amperes of current will flow through each resistance (R_{V} and R_{L}). Figure 4-33.—Shunt voltage regulator. Now, if the load resistance (R_{L}) increases, the current through R_{L} will decrease. For example, assume that the current through R_{L} is now 4 amperes and that the total current through R_{S} is 9 amperes. With this

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