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TUTORIAL 3 Q1 Draw and label a block diagram the elements of a DC power supply which receives an input from the 240 V; 50 Hz mains and produces an output of regulated 5 V DC. Describe briefly the function of each element. Illustrate your description with suitable figures.

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TUTORIAL 3 – VOLTAGE REGULATORS Solution

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TUTORIAL 3 SOLUTION (cont’d) Function of each element Transformer reduces (steps down) the 240 VAC to a suitably low AC value (See figure)

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TUTORIAL 3 Function of each element Rectifier converts the low VAC received from the transformer to pulsating VDC (See figure) SOLUTION (cont’d)

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TUTORIAL 3 SOLUTION (cont’d)

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TUTORIAL 3 Function of each element Smoothing circuit, also known as filter, minimizes the ripples appearing in the voltage waveform at the output of the rectifier. The output of this circuit is as smoothened waveform as in the following figure. SOLUTION (cont’d)

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TUTORIAL 3 SOLUTION (cont’d)

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Regulator maintains a constant output DC voltage (within certain percentage) despite variations, within certain limit, in either the line voltage (VAC), load or both. TUTORIAL 3 Function of each element SOLUTION (cont’d)

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TUTORIAL 3 Q2 Explain the following terms as applied to a voltage regulator; a)line regulation b)load regulation

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TUTORIAL 3 SOLUTION a)Line regulation as applied to a voltage regulator is a measure of its ability to maintain a constant output voltage despite variation in the input voltage. It is the change of output voltage per unit change in the input voltage and is normally expressed in percentage form, thus;

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TUTORIAL 3 b)Load regulation as applied to a voltage regulator is a measure its ability to maintain a constant output voltage despite variation in the load connected its terminal, and is normally express in percentage form, thus; SOLUTION (cont’d)

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TUTORIAL 3 Q3 The output voltage of a regulator is 30 V when not connected to any load. The rated maximum output current of the regulator is 1 A. It was found that output voltage at the maximum output current was 29.4 V. Determine the load regulation of the regulator.

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TUTORIAL 3 SOLUTION

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TUTORIAL 3 Q4 A voltage regulator is rated at a nominal output voltage of 12 V for the corresponding input voltage of 20 V. It is found that its output voltage decreases to V when the input voltage decreases to 16 V. Determine the line regulation of the regulator.

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TUTORIAL 3 SOLUTION

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TUTORIAL 3 Q5 Draw and label a block diagram showing the elements of a basic series regulator.

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TUTORIAL 3 SOLUTION

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TUTORIAL 3 Q6 The regulator in the following figure is to produce a nominal output voltage, V o = 18.6 V and a maximum load current I L(max) = 1 A. It is known that, the zener diode current I Z shall not drop to less than 15 mA, the current I 1 = 1 mA and the input voltage V i may vary between 22 V to 30 V. Determine the values of R 1, R 2 and R 3.

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TUTORIAL 3 Q6 (cont’d)

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TUTORIAL 3 SOLUTION Substituting values;

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TUTORIAL 3 Neglecting I ; SOLUTION (cont’d)

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TUTORIAL 3 Since it follows that; SOLUTION (cont’d)

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TUTORIAL 3 Neglecting I + ; Substituting values; SOLUTION (cont’d)

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TUTORIAL 3 Q7 For the shunt regulator shown in the following figure; a)find V o ; b)if I L and Vo are constant, find the change in I C1 if V i changes by 1 V; c)if the maximum input voltage V i = 25 V, find I L if the load resistance, R L is shorted

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TUTORIAL 3 Q7 (cont’d)

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TUTORIAL 3 a) SOLUTION

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TUTORIAL 3 If I L and V o are constant, I 3 will also be constant. Hence; b) SOLUTION (cont’d)

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TUTORIAL 3 When R L is shorted, V o = 0. Therefore; c) SOLUTION (cont’d)

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TUTORIAL 3 Q8 Describe the operation of the following regulator;

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TUTORIAL 3 If the load resistance R L suddenly decreases, the output voltage V o will also decrease. The decrease in V o will be followed by a decrease in V 4. The output of the op-amp V OA decreases because V OA = A O (V 4 – V Z ) and V Z being constant. SOLUTION

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TUTORIAL 3 The drop in V OA reduces the V BE bias voltage of Q 1 and hence reduces I C1. The reduction in I C1 means more of I R1 can flow through R L and thereby increases the output voltage V o. This increase compensates for the previous drop in V o. SOLUTION (cont’d)

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TUTORIAL 3 SOLUTION (cont’d)

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TUTORIAL 3 Q9 Draw and label a block diagram showing the elements of a basic shunt regulator.

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TUTORIAL 3 The block diagram of a basic shunt regulator; SOLUTION (cont’d)

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TUTORIAL 3 Q10 Describe the operation of the following regulator;

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TUTORIAL 3 DESCRIPTION TO FOLLOW SOLUTION

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