Exercise 1: EXERCISE OBJECTIVE DISCUSSION. a. circuit A. b. circuit B. Festo Didactic P0 75

Transcription

1 Exercise 1: EXERCISE OBJECTIVE DISCUSSION a. circuit A. b. circuit B. Festo Didactic P0 75

2 individual diodes are designated D instead of CR, with the diode circle symbol omitted.) The input terminals are sometimes marked with a sine wave symbol that indicates the ac input side of the bridge. 76 Festo Didactic P0

3 The output terminals are typically marked with plus (+) and minus ( ) symbols that indicate the positive and negative dc output sides of the bridge. a. sine wave symbols. b. plus (+) and minus ( ) symbols. When the bridge is in operation, one pair of diodes conducts at a time. One diode pair is D1 and D3, and the other pair is D2 and D4. Because of the diode pairing, both alternations of the ac input signal are converted to pulsating dc, which As shown, the positive input alternation causes diodes D1 and D3 to be forward biased. Festo Didactic P0 77

4 Because diodes D2 and D4 are reverse biased and do not conduct, they are not shown. During positive alternations of the ac input, diodes D1 and D3 are a. forward biased and permit current through D3, R1, and D1. b. through D2, the load resistor (R1), and back to the transformer through D4. During the negative alternation, diodes D1 and D3 are reverse biased and do not conduct, so they are not shown. When diodes D2 and D4 are forward biased during negative ac input alternations, the dc output is a a. negative pulse. b. positive pulse. Both the positive and negative alternations of the input ac voltage are converted to pulsating dc. The pulsating dc output results from the diode pairs steering the current through the load resistance in the same direction during positive and negative ac input alternations. 78 Festo Didactic P0

5 Because there are two dc pulses for one complete cycle of the input ac waveform, the output pulse During positive and negative alternations of the ac input, the current a. different directions. b. the same direction. a. equal to the ac input frequency. b. two times the ac input frequency. output voltage (V o(pk) ) equals the peak input voltage (V i(pk) ) minus the forward voltage drop (V F ) of the two conducting diodes: V o(pk) = V i(pk) 2(V F ) = V i(pk) 2(0.6) = V i(pk) 1.2 (approximately) The output rms voltage (V o(rms) ) equals times the peak output voltage (V o(pk) ). V o(rms) = x V o(pk) Festo Didactic P0 79

6 The output average voltage (V o(avg) ) equals times the peak output voltage (V o(pk) ). V o(avg) = x V o(pk) If the peak output voltage is 10.0 V o(pk), calculate the average output voltage (V o(avg) ). V o(avg) = V (Recall Value 1) PROCEDURE Locate the FULL-WAVE RECTIFICATION WITH POWER SUPPLY FILTERS circuit block, and connect the circuit shown. Resistor R1 is the a. b. load resistor. 80 Festo Didactic P0

7 and 2 probes to X10. Connect the oscilloscope channel 1 probe to the top GEN terminal and its ground clip to the bottom GEN terminal. Festo Didactic P0 81

8 Connect the channel 2 probe to the top terminal of the T1 secondary coil and its ground clip to the bottom terminal. Adjust the generator for a 20 V pk-pk, 100 Hz sine wave at the T1secondary coil, which is shown on oscilloscope channel 2. Compare the transformer secondary peak-to-peak voltage on channel 2 to the primary voltage on channel 1. Observe that the transformer primary and secondary signals are in phase. 82 Festo Didactic P0

9 Does the transformer primary-to-secondary have a step-down or step-up voltage relationship? a. step-down b. step-up Observe the output across R1 by connecting the channel 2 probe to the positive (+) output ( ) test point of the bridge. NOTE: same time because grounding both the transformer secondary coil and the negative ( ) bridge output Festo Didactic P0 83

10 a. yes b. no Measure the frequency (f) of the dc output pulsations across the R1 load resistance on channel 2 of the oscilloscope. f = Hz (Recall Value 1) Measure the peak dc output voltage (V o(pk) ). V o(pk) = V (Recall Value 2) Calculate the dc average output voltage (V o(avg) ). Use the following equation with your measured value of V o(pk) ( V [Step 12, Recall Value 2]). V o(avg) = x V o(pk) V o(avg) = V (Recall Value 3) 84 Festo Didactic P0

11 Set your multimeter to dc volts. Measure the circuit average dc output voltage across R1. The meter common connects to the negative ( ) output terminal. V o(avg) = V (Recall Value 4) The transformer secondary coil output was set to 20 V pk-pk, or a peak voltage of 10 V pk. Value 2). V pk (Step 12, Recall The difference is due to the a. transformer coil voltage drop. b. forward voltage drop of the two diodes. Adjust the ac input signal at the output of the generator to 10 V pk-pk on channel 1. Set the channel 2 coupling to ground and adjust the channel 2 ground sweep on the second horizontal line from the bottom of the oscilloscope screen. Festo Didactic P0 85

12 Observe the signal across D2 by connecting the channel 2 probe to the top terminal of the T1 secondary coil and the ground clip to the negative ( ) bridge output terminal, as shown. Set the channel 2 coupling to dc. The channel 1 and 2 oscilloscope waveforms should appear as shown. When diode D2 is conducting, its voltage drop (shown by the channel 2 waveform) is the same as the a. negative (highlighted) portions of the waveform. b. positive portion of the waveform. On the oscilloscope screen, measure the voltage drop across D2 (V D2 ) when it is conducting. Measure V D2 from the ground reference line. V D2 = V (Recall Value 5) 86 Festo Didactic P0

13 During the negative (highlighted) portion of the channel 2 waveform, D2 is a. reverse biased. b. forward biased. D2 is forward biased during which alternation of the ac input waveform on channel 1? a. negative b. positive What other diode in this circuit is forward biased during the negative alternation of the input waveform? a. D1 b. D3 c. D4 The positive voltage portion of the oscilloscope channel 2 waveform is across a. diode D1 and load resistor R1. b. load resistor R1. c. diode D4. During the positive portion of the input waveform, D1 is a. reverse biased. b. forward biased. Festo Didactic P0 87

14 What other diode in this circuit is forward biased during the positive alternation of the input waveform? a. D2 b. D3 c. D4 Connect the channel 2 probe to the positive (+) terminal of the bridge. a. D3, R1, and D1. b. D2, R1, and D4. a. D3, R1, and D1. b. D2, R1, and D4. CONCLUSION voltage. The output dc ripple frequency is two times the ac input frequency. diodes at a time. The two conducting diodes steer the voltage so that the load current is always in the same direction. The peak dc output voltage is less than the peak ac input voltage by the forward voltage drop of the two conducting diodes. The average output voltage is times the peak output voltage. 88 Festo Didactic P0

15 REVIEW QUESTIONS 1. a. D1 with D2, and D3 with D4 b. D1 with D4, and D3 with D2 c. D1 with D3, and D2 with D4 d. All diodes: D1, D2, D3, and D4 2. a. positive ac input alternations into a pulsating dc output. b. negative ac input alternations into a pulsating dc output. c. negative and positive ac input alternations into a pulsating dc output. d. a pulsating dc input into an ac output. 3. a. only during negative input alternations. b. only during positive input alternations. c. only when the peak ac voltage is above 2 V. d. during positive and negative input alternations. 4. a. double the input frequency. b. the same as the input frequency. c. half of the input frequency. d. a function of the load resistance. 5. a. b. The peak dc output voltage is less than the peak ac input voltage by the forward voltage drop of the two conducting diodes. c. The average dc output voltage is times the peak output voltage. d. All of the above Festo Didactic P0 89