Full-wave Bridge Rectifier 1j4z54
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Electrical and Electronic Engineering
THE FULL-WAVE DIODE BRIDGE RECTIFIER
11/30/2011
Page 1 of 26
Contents Introduction ...................................................................................................................................... 3 Questions 1 to 10 - Calculations and simulated measurements ...................................................... 4 Full-wave diode bridge rectifier ....................................................................................................... 6 Question 11 – Ripple Voltage and output voltage harmonics. ........................................................ 8 Question 12 - Line Current Harmonics ........................................................................................... 13 Analysis for Question 11 - Ripple Voltage ...................................................................................... 18 Analysis for Question 12 - Line Current Harmonics ....................................................................... 20 Question 13 – Voltage Regulator Design........................................................................................ 22 Conclusion ...................................................................................................................................... 23 References ...................................................................................................................................... 24 Appendices ..................................................................................................................................... 25
Page 2 of 26
Introduction A bridge rectifier is a circuit design that converts an alternating current into direct current. This report looks at the full-wave diode bridge rectifier. The full-wave diode bridge rectifier consists of a combination of four diodes connected in square configuration. Typically this combination produces a pulsed DC output. The ‘humped’ characteristic of this pulsed output can be improved by connecting a capacitor across the load. This capacitor is often called the smoothing capacitor and this report will analysis the effects of adding this smoothing capacitor to a full-wave diode bridge rectifier.
Aim Use the program PSPICE to simulate and investigate the characteristics and operation of a full-wave bridge rectifier.
Objectives
Design a full-wave bridge rectifier circuit in the program PSPICE using suitable diodes.
Simulate the circuit and take a series of measurements and compare them to calculated values.
Determine and analyse the ripple voltage produced by the circuit with two different variations of smoothing capacitors.
Measure and analyse the harmonics for each capacitor variation up to 800Hz.
Determine the line current harmonics with the circuit configured with different loads and capacitors. Compare the results to the European Directive related the line current harmonics.
Page 3 of 26
Questions 1 to 10 - Calculations and simulated measurements 1) √
√
2)
Measured dc value from PSPICE Simulation = 2.19 A (Refer to Appendix 1) 3)
Measured dc output value from PSPICE Simulation = 45.7 W (Refer to Appendix 1) 4) √
√
Measured RMS output voltage from PSIPICE Simulation = 21.5 V (Refer to Appendix 1) 5)
√ 6)
Page 4 of 26
7)
8)
9) √
√
10) = 3.54 A √
Page 5 of 26
Full-wave diode bridge rectifier Figure 1.1 - Circuit design for full-wave bridge rectifier taken from PSPICE simulation
The diode selected for the circuit was the 1N5401. This diode was selected because it has current rating of 3.0 A and the calculated output current was 2.25 A so the 1N5401 was sufficient to handle the calculated current.
Page 6 of 26
Figure 1.2 - A graph to show the rectified output from the full-wave diode bridge rectifier.
The blue trace is the output power (W) measured at the load, with peak of 117 W. The green trace is the voltage output (V) measured at the load, with a peak of 34.5 V. The yellow trace is the RMS value of the output voltage measured at the load, with a value of 22.3 V. The red trace is the current output measured at the load, with a value of 2.19 A. Page 7 of 26
Question 11 – Ripple Voltage and output voltage harmonics. Figure 1.3 - Full-wave diode bridge rectifier circuit including 600uF smoothing capacitor.
A capacitor has been placed across the load to smooth the output from the full-wave bridge rectifier. The results are shown in Figures 1.4 to 1.9 on the next few pages. Calculation for ripple voltage,
Page 8 of 26
Figure 1.4 - A graph from the simulation of full-wave bridge rectifier with 600uF smoothing capacitor to show the smoothed output
Page 9 of 26
Figure 1.5 - A graph to show the voltage harmonics from the simulation of the Full-Wave Bridge Rectifier with a 600uF smoothing capacitor
Green Trace = Voltage Harmonics up to 800 kHz. Figure 1.6 - Table of results from circuit simulation with 600 uF capacitor connected in the circuit.
Harmonic Order Voltage Peak (V)
1st 9.75
2nd 1.8
3rd 0.86
4th 0.25
5th 0.052
6th 0.149
7th 0.205
8th 0.211 Page 10 of 26
Refer to Appendix 2 for the circuit design used to evaluate the 2200uF smoothing capacitor placed in the circuit. Figure 1.7 – A graph from the simulation of full-wave bridge rectifier with 2200uF smoothing capacitor to show the smoothed output.
Page 11 of 26
Figure 1.8 - A graph to show the voltage Harmonics from the simulation of the Full-Wave Bridge Rectifier with a 2200uF smoothing capacitor
Green Trace = Voltage Harmonics up to 800 kHz. Figure 1.9 - Table of results from circuit simulation with 2200 uF capacitor connected in the circuit.
Harmonic Order 1st 2nd 3rd 4th 5th 6th 7th 8th Voltage Peak (V) 5.25 1.49 0.364 0.624 0.52 0.243 0.225 0.295 st The amplitude of the 1 voltage is nearly halved by using a 2200 uF capacitor instead of a 600 uF capacitor. Page 12 of 26
Question 12 - Line Current Harmonics Figure 2.0 - Circuit used to simulate the line currents of a Full-Wave Bridge Rectifier with a 500uF smoothing capacitor and a 10 Ω load.
The measurements for the line current harmonics were taken from the output of the Power Source show with the yellow probe. The results of the measurements with various capacitors and loads connected are show below.
Page 13 of 26
Figure 2.1 - Graph of the output voltage harmonics from the Full-Wave Bridge Rectifier with a 500uF smoothing capacitor and 10 Ω load.
The yellow trace on the graph represents the line current harmonics up to 1 kHz. Figure 2.2 - Table of results from circuit with capacitor value of 500uF and load of 10Ω. Harmonic Number 1st 2nd 3rd 4th 5th 6th Harmonic Frequency (Hz) 40.5 140 239 341 441 560 Harmonic Magnitude (A) 3.21 1.63 0.65 0.48 0.32 0.26 Calculated (mA/W) 27.4 13.9 5.6 4.1 2.7 2.2 Max Permissible (mA/W) n/a n/a 3.4 n/a 1.9 n/a
7th 661 0.24 2.1 1
8th 760 0.20 1.7 n/a
9th 860 0.17 1.5 0.5
10th 940 0.15 1.3 n/a
15th 1460 0.10 0.9 0.26
39th 3800 0.01 0.1 0.098 Page 14 of 26
Figure 2.3 - Graph of the output voltage harmonics from the Full-Wave Bridge Rectifier with a 500uF smoothing capacitor and 50 Ω load.
The yellow trace on the graph represents the line current harmonics up to 1 kHz. Figure 2.4 - Table of results from circuit with capacitor value of 500uF and load of 50Ω. Harmonic Number 1st 2nd 3rd 4th 5th 6th Frequency (Hz) 40.2 140 260 361 441 541 Harmonic Magnitude (A) 1.23 1.02 0.52 0.29 0.23 0.21 Calculated (mA/W) 10.5 8.7 4.4 2.5 2.0 1.8 Max Permissible (mA/W) n/a n/a 3.4 n/a 1.9 n/a
7th 661 0.18 1.5 1
8th 761 0.11 0.9 n/a
9th 840 0.14 1.2 0.5
10th 941 0.10 0.9 n/a
15th 1460 0.07 0.6 0.26
39th 3760 0.02 0.2 0.098 Page 15 of 26
Figure 2.5 - Graph of the output voltage harmonics from the Full-Wave Bridge Rectifier with a 2000uF smoothing capacitor and 10 Ω load.
The yellow trace on the graph represents the line current harmonics up to 1 kHz. Figure 2.6 - Table of results from circuit with capacitor value of 2000uF and load of 10Ω. Harmonic Number 1st 2nd 3rd 4th 5th 6th Harmonic Frequency (Hz) 40.4 139 259 361 440 541 Harmonic Magnitude (A) 5.54 4.46 2.14 1.26 0.89 0.96 Calculated (mA/W) 47.4 38.1 18.3 10.8 7.6 8.2 Max Permissible (mA/W) n/a n/a 3.4 n/a 1.9 n/a
7th 661 0.67 5.7 1
8th 760 0.60 5.1 n/a
9th 841 0.47 4.0 0.5
10th 939 0.51 4.4 n/a
15th 1440 0.24 2.1 0.26
39th 3800 0.02 0.2 0.098 Page 16 of 26
Figure 2.7 - Graph of the output voltage harmonics from the Full-Wave Bridge Rectifier with a 2000 uF smoothing capacitor and 50 Ω load.
The yellow trace on the graph represents the line current harmonics up to 1 kHz. Figure 2.8 - Table of results from circuit with capacitor value of 2000uF and load of 50Ω. Harmonic Number 1st 2nd 3rd 4th 5th 6th Harmonic Frequency (Hz) 40 80 140 260 340 460 Harmonic Magnitude (A) 3.23 2.18 2.22 1.16 1.02 0.71 Calculated (mA/W) 27.6 18.6 19.0 9.9 8.7 6.1 Max Permissible (mA/W) n/a n/a 3.4 n/a 1.9 n/a
7th 560 0.41 3.5 1
8th 640 0.47 4.0 n/a
9th 760 0.40 3.4 0.5
10th 840 0.28 2.4 n/a
15th 1360 0.16 1.4 0.26
39th 3460 0.04 0.3 0.098 Page 17 of 26
Analysis for Question 11 - Ripple Voltage With a capacitor of 600uF connected in parallel with the load the voltage output is transformed from a continuous positive half sine wave as seen in Fig 1.2 to a continuous ripple with a smaller voltage swing (peak to peak) as seen in Fig 1.4. The voltage swing has been reduced from 34.1 V to 20.6 V by introducing a capacitor into the circuit. So the average voltage is higher at 22.3 V with the capacitor connected compared with the average voltage of 25.1 V for the circuit with no smoothing capacitor. The measured value (20.6 V) of the ripple voltage from PSPICE is low compared to the calculated value of 37.2 V this difference could be due to the fact that the equation is fairly simplistic and does not take into all of the factors such as the saw-tooth shape of the waveform. The output from the full-wave capacitor is smoothed by the capacitor because, as the output voltage increases the capacitor is charged and then as the output voltage begins to decrease and return to zero the capacitor discharges the energy it has stored from the voltage previously increasing. This happens every cycle and so the capacitor prevents the output voltage from ever reaching zero therefore making the output become closer to the straight line of an ideal dc output. With a capacitor of 2200 uF connected in parallel with the load the voltage output was smoothed even further. The voltage swing was measured from the PSPICE simulation at 9.5 V, see Fig 1.7. This was fairly close to the calculated value of 10.2 V. This would suggest that the calculation used to calculate the ripple voltage works best when the ripple voltage is relatively small. The larger capacitor smoothes the output more effectively as it is able to store a larger charge on the upward trend of the output then discharge more energy on the downward output trend. Therefore in the graphical sense the larger capacitor is able to fill in more of gap left between the output ‘humps’ of the full-wave bridge rectifier. This larger capacitor brings the output even closer the ideal straight line output. For example in a 10,000 uF capacitor was used the ripple voltage would be reduced even further:
Page 18 of 26
2.24 V is a small ripple voltage but the rectifier output would still not be an ideal dc output. The capacitor would have to be increased to 100,000 uF to produce a ripple voltage of 0.22 V which would be very close to the ideal dc output. But having a capacitor of this high value may have detrimental effects of the other characteristics on the circuit such as increasing the current to intolerable values.
Page 19 of 26
Analysis for Question 12 - Line Current Harmonics The European Directive that governs the amplitudes of line current harmonics is IEC 610003-2, ‘Electromagnetic compatibility (EMC) – Part 3-2 – Limits for harmonic current emissions (equipment input current ≤ 16 A per phase)’. This analysis is based on the fact that the circuit used for this assignment would be in the Class D category because the circuit could be part of circuitry used in Personal Computers and monitors/televisions. In the results for this question (Figures 2.1 to 2.8) the maximum mA/W limit has been placed along with the calculated mA/W limit. Where the specific harmonic complies with the EU directive IEC 61000-3-2 the value has been highlighted green. Where the harmonic value does not comply with IEC 61000-3-2 with the limit has been highlighted red. Of course if just one of the values is above the set limit then circuit will not as legal but the colour coding gives an idea of where the circuit is complying and not complying with IEC 61000-3-2. In all of the circuit configurations simulated all the harmonics (mA/W) were higher than the limit set by the EU directive IEC 61000-3-2. So all of the circuits would fail to comply with the standard and not be deemed legal to be sold within the EU. These high harmonic amplitudes were caused by the combination of the large capacitor and small load resistor. The equations, current in a capacitor, ( )
( )
and ohm’s law
mean that the
current has to be high with a high capacitor and low load resistance. With the load increased to 1000 Ω (See results in Appendix 3) a reduction of the harmonics can be seen and some of the harmonic values would comply with IEC 61000-3-2. In this circuit the high load resistance was limiting the current generated in the harmonics. Why do harmonics occur? Harmonics occur in the line current in the supply because non-linear components (the four diodes) draw current disproportionably to the source voltage therefore causing nonsinusoidal current waveforms to be produced.
Page 20 of 26
How can the circuit be improved to minimise the harmonic amplitudes? The introduction of a higher load resistance would decrease the harmonic amplitude and also allow a fairly large capacitor to be used meaning the ripple voltage can be made a small as practicable. See Appendix 3 for results of simulating the circuit with a 1000 Ω load resistance. The results in Appendix 3 show very small harmonic magnitudes across the whole frequency range measured. So with a 1000 Ω load resistance the circuit would easily comply with the EU directive 61000-3-2. Another way to improve the full-wave diode bridge rectifier would be to place a ‘choke’ the circuit. This inductor would have high impedance which would limit the ripples produced in the output.
Page 21 of 26
Question 13 – Voltage Regulator Design Figure 2.9 – Circuit design for the voltage regulator. 22.5 V R1
Load 10 Ω 0V
This circuit is designed to output 12 V d.c to the 10 Ω load. The zener diode selected for the circuit is the 1N4740A. This diode has a Zener Voltage of 10 V and a Zener Current value of 25 mA at 10 V. The Bi-polar transisitor choosen was the ZXTN25100BFHTA which has a hfe value of 100 and a max collector current of 3A. The datasheets for the selected zener diode and BJT are referenced in the references section of the assignment. Calculations for cirucit are as follows.
So use 360 Ω from e24 resistor range.
Page 22 of 26
Conclusion
The aim of this assignment was to use the program PSPICE to simulate and investigate the characteristics and operation of a full-wave bridge rectifier.
The results were that the voltage ripple can be reduced by fitting a smoothing capacitor across the load.
By increasing the size of the smoothing capacitor the voltage ripple and voltage harmonics can be reduced further.
For the line current harmonics section of the assignment it was found that none of the four circuits simulated would comply with the EU Directive IEC 61000-3-2.
It was suggested that for a circuit to comply with IEC 61000-3-2 the load resistance needs to be high enough to limit the harmonic magnitudes whilst the capacitor needs to be large to provide a small ripple voltage.
A design of a voltage regulator was produced to supply a steady 12 V d.c output.
To further investigate this circuit an inductor could be added to the circuit either before or after the bridge. This could be then simulated to find if the inductor would improve the line current harmonics and the rectifier output.
Page 23 of 26
References http://en.wikipedia.org/wiki/Rectifier http://en.wikipedia.org/wiki/Capacitor http://www.allaboutcircuits.com/vol_2/chpt_10/7.html http://en.wikipedia.org/wiki/Ripple_(electrical) http://www.epsma.org/pdf/PFC Guide_November 2010.pdf http://www.datasheetcatalog.com/datasheets_pdf/1/N/5/4/1N5401.shtml
Zenor Diode Datasheet http://www.datasheetcatalog.com/datasheets_pdf/1/N/4/7/1N4740A.shtml BJT Datasheet http://parts.digikey.com/1/parts/1009597-transistor-npn-100v-3a-sot23-3-zxtn25100bfhta.html
Page 24 of 26
Appendices Appendix 1 – Graph from PSPICE simulation of full-wave diode bridge rectifier.
Appendix 2 – Full-wave diode bridge rectifier circuit including 2200uF smoothing capacitor.
Page 25 of 26
Appendix 3 - Table of results from circuit with capacitor value of 600uF and load of 1kΩ. Harmonic Number 1st 2nd 3rd 4th 5th 6th 40 260 340 380 460 540 Harmonic Frequency (Hz) Harmonic Magnitude (A) 0.694 0.134 0.153 0.101 0.1 0.103 Calculated (mA/W) 5.9 1.1 1.3 0.9 0.9 0.9 Max Permissible (mA/W) n/a n/a 3.4 n/a 1.9 n/a
7th
8th
9th
10th
15th
39th
580
660
740
800
1140
3040
0.06 0.5 1
0.08 0.7 n/a
0.07 0.6 0.5
0.04 0.3 n/a
0.03 0.3 0.26
0.01 0.1 0.098
Page 26 of 26
THE FULL-WAVE DIODE BRIDGE RECTIFIER
11/30/2011
Page 1 of 26
Contents Introduction ...................................................................................................................................... 3 Questions 1 to 10 - Calculations and simulated measurements ...................................................... 4 Full-wave diode bridge rectifier ....................................................................................................... 6 Question 11 – Ripple Voltage and output voltage harmonics. ........................................................ 8 Question 12 - Line Current Harmonics ........................................................................................... 13 Analysis for Question 11 - Ripple Voltage ...................................................................................... 18 Analysis for Question 12 - Line Current Harmonics ....................................................................... 20 Question 13 – Voltage Regulator Design........................................................................................ 22 Conclusion ...................................................................................................................................... 23 References ...................................................................................................................................... 24 Appendices ..................................................................................................................................... 25
Page 2 of 26
Introduction A bridge rectifier is a circuit design that converts an alternating current into direct current. This report looks at the full-wave diode bridge rectifier. The full-wave diode bridge rectifier consists of a combination of four diodes connected in square configuration. Typically this combination produces a pulsed DC output. The ‘humped’ characteristic of this pulsed output can be improved by connecting a capacitor across the load. This capacitor is often called the smoothing capacitor and this report will analysis the effects of adding this smoothing capacitor to a full-wave diode bridge rectifier.
Aim Use the program PSPICE to simulate and investigate the characteristics and operation of a full-wave bridge rectifier.
Objectives
Design a full-wave bridge rectifier circuit in the program PSPICE using suitable diodes.
Simulate the circuit and take a series of measurements and compare them to calculated values.
Determine and analyse the ripple voltage produced by the circuit with two different variations of smoothing capacitors.
Measure and analyse the harmonics for each capacitor variation up to 800Hz.
Determine the line current harmonics with the circuit configured with different loads and capacitors. Compare the results to the European Directive related the line current harmonics.
Page 3 of 26
Questions 1 to 10 - Calculations and simulated measurements 1) √
√
2)
Measured dc value from PSPICE Simulation = 2.19 A (Refer to Appendix 1) 3)
Measured dc output value from PSPICE Simulation = 45.7 W (Refer to Appendix 1) 4) √
√
Measured RMS output voltage from PSIPICE Simulation = 21.5 V (Refer to Appendix 1) 5)
√ 6)
Page 4 of 26
7)
8)
9) √
√
10) = 3.54 A √
Page 5 of 26
Full-wave diode bridge rectifier Figure 1.1 - Circuit design for full-wave bridge rectifier taken from PSPICE simulation
The diode selected for the circuit was the 1N5401. This diode was selected because it has current rating of 3.0 A and the calculated output current was 2.25 A so the 1N5401 was sufficient to handle the calculated current.
Page 6 of 26
Figure 1.2 - A graph to show the rectified output from the full-wave diode bridge rectifier.
The blue trace is the output power (W) measured at the load, with peak of 117 W. The green trace is the voltage output (V) measured at the load, with a peak of 34.5 V. The yellow trace is the RMS value of the output voltage measured at the load, with a value of 22.3 V. The red trace is the current output measured at the load, with a value of 2.19 A. Page 7 of 26
Question 11 – Ripple Voltage and output voltage harmonics. Figure 1.3 - Full-wave diode bridge rectifier circuit including 600uF smoothing capacitor.
A capacitor has been placed across the load to smooth the output from the full-wave bridge rectifier. The results are shown in Figures 1.4 to 1.9 on the next few pages. Calculation for ripple voltage,
Page 8 of 26
Figure 1.4 - A graph from the simulation of full-wave bridge rectifier with 600uF smoothing capacitor to show the smoothed output
Page 9 of 26
Figure 1.5 - A graph to show the voltage harmonics from the simulation of the Full-Wave Bridge Rectifier with a 600uF smoothing capacitor
Green Trace = Voltage Harmonics up to 800 kHz. Figure 1.6 - Table of results from circuit simulation with 600 uF capacitor connected in the circuit.
Harmonic Order Voltage Peak (V)
1st 9.75
2nd 1.8
3rd 0.86
4th 0.25
5th 0.052
6th 0.149
7th 0.205
8th 0.211 Page 10 of 26
Refer to Appendix 2 for the circuit design used to evaluate the 2200uF smoothing capacitor placed in the circuit. Figure 1.7 – A graph from the simulation of full-wave bridge rectifier with 2200uF smoothing capacitor to show the smoothed output.
Page 11 of 26
Figure 1.8 - A graph to show the voltage Harmonics from the simulation of the Full-Wave Bridge Rectifier with a 2200uF smoothing capacitor
Green Trace = Voltage Harmonics up to 800 kHz. Figure 1.9 - Table of results from circuit simulation with 2200 uF capacitor connected in the circuit.
Harmonic Order 1st 2nd 3rd 4th 5th 6th 7th 8th Voltage Peak (V) 5.25 1.49 0.364 0.624 0.52 0.243 0.225 0.295 st The amplitude of the 1 voltage is nearly halved by using a 2200 uF capacitor instead of a 600 uF capacitor. Page 12 of 26
Question 12 - Line Current Harmonics Figure 2.0 - Circuit used to simulate the line currents of a Full-Wave Bridge Rectifier with a 500uF smoothing capacitor and a 10 Ω load.
The measurements for the line current harmonics were taken from the output of the Power Source show with the yellow probe. The results of the measurements with various capacitors and loads connected are show below.
Page 13 of 26
Figure 2.1 - Graph of the output voltage harmonics from the Full-Wave Bridge Rectifier with a 500uF smoothing capacitor and 10 Ω load.
The yellow trace on the graph represents the line current harmonics up to 1 kHz. Figure 2.2 - Table of results from circuit with capacitor value of 500uF and load of 10Ω. Harmonic Number 1st 2nd 3rd 4th 5th 6th Harmonic Frequency (Hz) 40.5 140 239 341 441 560 Harmonic Magnitude (A) 3.21 1.63 0.65 0.48 0.32 0.26 Calculated (mA/W) 27.4 13.9 5.6 4.1 2.7 2.2 Max Permissible (mA/W) n/a n/a 3.4 n/a 1.9 n/a
7th 661 0.24 2.1 1
8th 760 0.20 1.7 n/a
9th 860 0.17 1.5 0.5
10th 940 0.15 1.3 n/a
15th 1460 0.10 0.9 0.26
39th 3800 0.01 0.1 0.098 Page 14 of 26
Figure 2.3 - Graph of the output voltage harmonics from the Full-Wave Bridge Rectifier with a 500uF smoothing capacitor and 50 Ω load.
The yellow trace on the graph represents the line current harmonics up to 1 kHz. Figure 2.4 - Table of results from circuit with capacitor value of 500uF and load of 50Ω. Harmonic Number 1st 2nd 3rd 4th 5th 6th Frequency (Hz) 40.2 140 260 361 441 541 Harmonic Magnitude (A) 1.23 1.02 0.52 0.29 0.23 0.21 Calculated (mA/W) 10.5 8.7 4.4 2.5 2.0 1.8 Max Permissible (mA/W) n/a n/a 3.4 n/a 1.9 n/a
7th 661 0.18 1.5 1
8th 761 0.11 0.9 n/a
9th 840 0.14 1.2 0.5
10th 941 0.10 0.9 n/a
15th 1460 0.07 0.6 0.26
39th 3760 0.02 0.2 0.098 Page 15 of 26
Figure 2.5 - Graph of the output voltage harmonics from the Full-Wave Bridge Rectifier with a 2000uF smoothing capacitor and 10 Ω load.
The yellow trace on the graph represents the line current harmonics up to 1 kHz. Figure 2.6 - Table of results from circuit with capacitor value of 2000uF and load of 10Ω. Harmonic Number 1st 2nd 3rd 4th 5th 6th Harmonic Frequency (Hz) 40.4 139 259 361 440 541 Harmonic Magnitude (A) 5.54 4.46 2.14 1.26 0.89 0.96 Calculated (mA/W) 47.4 38.1 18.3 10.8 7.6 8.2 Max Permissible (mA/W) n/a n/a 3.4 n/a 1.9 n/a
7th 661 0.67 5.7 1
8th 760 0.60 5.1 n/a
9th 841 0.47 4.0 0.5
10th 939 0.51 4.4 n/a
15th 1440 0.24 2.1 0.26
39th 3800 0.02 0.2 0.098 Page 16 of 26
Figure 2.7 - Graph of the output voltage harmonics from the Full-Wave Bridge Rectifier with a 2000 uF smoothing capacitor and 50 Ω load.
The yellow trace on the graph represents the line current harmonics up to 1 kHz. Figure 2.8 - Table of results from circuit with capacitor value of 2000uF and load of 50Ω. Harmonic Number 1st 2nd 3rd 4th 5th 6th Harmonic Frequency (Hz) 40 80 140 260 340 460 Harmonic Magnitude (A) 3.23 2.18 2.22 1.16 1.02 0.71 Calculated (mA/W) 27.6 18.6 19.0 9.9 8.7 6.1 Max Permissible (mA/W) n/a n/a 3.4 n/a 1.9 n/a
7th 560 0.41 3.5 1
8th 640 0.47 4.0 n/a
9th 760 0.40 3.4 0.5
10th 840 0.28 2.4 n/a
15th 1360 0.16 1.4 0.26
39th 3460 0.04 0.3 0.098 Page 17 of 26
Analysis for Question 11 - Ripple Voltage With a capacitor of 600uF connected in parallel with the load the voltage output is transformed from a continuous positive half sine wave as seen in Fig 1.2 to a continuous ripple with a smaller voltage swing (peak to peak) as seen in Fig 1.4. The voltage swing has been reduced from 34.1 V to 20.6 V by introducing a capacitor into the circuit. So the average voltage is higher at 22.3 V with the capacitor connected compared with the average voltage of 25.1 V for the circuit with no smoothing capacitor. The measured value (20.6 V) of the ripple voltage from PSPICE is low compared to the calculated value of 37.2 V this difference could be due to the fact that the equation is fairly simplistic and does not take into all of the factors such as the saw-tooth shape of the waveform. The output from the full-wave capacitor is smoothed by the capacitor because, as the output voltage increases the capacitor is charged and then as the output voltage begins to decrease and return to zero the capacitor discharges the energy it has stored from the voltage previously increasing. This happens every cycle and so the capacitor prevents the output voltage from ever reaching zero therefore making the output become closer to the straight line of an ideal dc output. With a capacitor of 2200 uF connected in parallel with the load the voltage output was smoothed even further. The voltage swing was measured from the PSPICE simulation at 9.5 V, see Fig 1.7. This was fairly close to the calculated value of 10.2 V. This would suggest that the calculation used to calculate the ripple voltage works best when the ripple voltage is relatively small. The larger capacitor smoothes the output more effectively as it is able to store a larger charge on the upward trend of the output then discharge more energy on the downward output trend. Therefore in the graphical sense the larger capacitor is able to fill in more of gap left between the output ‘humps’ of the full-wave bridge rectifier. This larger capacitor brings the output even closer the ideal straight line output. For example in a 10,000 uF capacitor was used the ripple voltage would be reduced even further:
Page 18 of 26
2.24 V is a small ripple voltage but the rectifier output would still not be an ideal dc output. The capacitor would have to be increased to 100,000 uF to produce a ripple voltage of 0.22 V which would be very close to the ideal dc output. But having a capacitor of this high value may have detrimental effects of the other characteristics on the circuit such as increasing the current to intolerable values.
Page 19 of 26
Analysis for Question 12 - Line Current Harmonics The European Directive that governs the amplitudes of line current harmonics is IEC 610003-2, ‘Electromagnetic compatibility (EMC) – Part 3-2 – Limits for harmonic current emissions (equipment input current ≤ 16 A per phase)’. This analysis is based on the fact that the circuit used for this assignment would be in the Class D category because the circuit could be part of circuitry used in Personal Computers and monitors/televisions. In the results for this question (Figures 2.1 to 2.8) the maximum mA/W limit has been placed along with the calculated mA/W limit. Where the specific harmonic complies with the EU directive IEC 61000-3-2 the value has been highlighted green. Where the harmonic value does not comply with IEC 61000-3-2 with the limit has been highlighted red. Of course if just one of the values is above the set limit then circuit will not as legal but the colour coding gives an idea of where the circuit is complying and not complying with IEC 61000-3-2. In all of the circuit configurations simulated all the harmonics (mA/W) were higher than the limit set by the EU directive IEC 61000-3-2. So all of the circuits would fail to comply with the standard and not be deemed legal to be sold within the EU. These high harmonic amplitudes were caused by the combination of the large capacitor and small load resistor. The equations, current in a capacitor, ( )
( )
and ohm’s law
mean that the
current has to be high with a high capacitor and low load resistance. With the load increased to 1000 Ω (See results in Appendix 3) a reduction of the harmonics can be seen and some of the harmonic values would comply with IEC 61000-3-2. In this circuit the high load resistance was limiting the current generated in the harmonics. Why do harmonics occur? Harmonics occur in the line current in the supply because non-linear components (the four diodes) draw current disproportionably to the source voltage therefore causing nonsinusoidal current waveforms to be produced.
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How can the circuit be improved to minimise the harmonic amplitudes? The introduction of a higher load resistance would decrease the harmonic amplitude and also allow a fairly large capacitor to be used meaning the ripple voltage can be made a small as practicable. See Appendix 3 for results of simulating the circuit with a 1000 Ω load resistance. The results in Appendix 3 show very small harmonic magnitudes across the whole frequency range measured. So with a 1000 Ω load resistance the circuit would easily comply with the EU directive 61000-3-2. Another way to improve the full-wave diode bridge rectifier would be to place a ‘choke’ the circuit. This inductor would have high impedance which would limit the ripples produced in the output.
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Question 13 – Voltage Regulator Design Figure 2.9 – Circuit design for the voltage regulator. 22.5 V R1
Load 10 Ω 0V
This circuit is designed to output 12 V d.c to the 10 Ω load. The zener diode selected for the circuit is the 1N4740A. This diode has a Zener Voltage of 10 V and a Zener Current value of 25 mA at 10 V. The Bi-polar transisitor choosen was the ZXTN25100BFHTA which has a hfe value of 100 and a max collector current of 3A. The datasheets for the selected zener diode and BJT are referenced in the references section of the assignment. Calculations for cirucit are as follows.
So use 360 Ω from e24 resistor range.
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Conclusion
The aim of this assignment was to use the program PSPICE to simulate and investigate the characteristics and operation of a full-wave bridge rectifier.
The results were that the voltage ripple can be reduced by fitting a smoothing capacitor across the load.
By increasing the size of the smoothing capacitor the voltage ripple and voltage harmonics can be reduced further.
For the line current harmonics section of the assignment it was found that none of the four circuits simulated would comply with the EU Directive IEC 61000-3-2.
It was suggested that for a circuit to comply with IEC 61000-3-2 the load resistance needs to be high enough to limit the harmonic magnitudes whilst the capacitor needs to be large to provide a small ripple voltage.
A design of a voltage regulator was produced to supply a steady 12 V d.c output.
To further investigate this circuit an inductor could be added to the circuit either before or after the bridge. This could be then simulated to find if the inductor would improve the line current harmonics and the rectifier output.
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References http://en.wikipedia.org/wiki/Rectifier http://en.wikipedia.org/wiki/Capacitor http://www.allaboutcircuits.com/vol_2/chpt_10/7.html http://en.wikipedia.org/wiki/Ripple_(electrical) http://www.epsma.org/pdf/PFC Guide_November 2010.pdf http://www.datasheetcatalog.com/datasheets_pdf/1/N/5/4/1N5401.shtml
Zenor Diode Datasheet http://www.datasheetcatalog.com/datasheets_pdf/1/N/4/7/1N4740A.shtml BJT Datasheet http://parts.digikey.com/1/parts/1009597-transistor-npn-100v-3a-sot23-3-zxtn25100bfhta.html
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Appendices Appendix 1 – Graph from PSPICE simulation of full-wave diode bridge rectifier.
Appendix 2 – Full-wave diode bridge rectifier circuit including 2200uF smoothing capacitor.
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Appendix 3 - Table of results from circuit with capacitor value of 600uF and load of 1kΩ. Harmonic Number 1st 2nd 3rd 4th 5th 6th 40 260 340 380 460 540 Harmonic Frequency (Hz) Harmonic Magnitude (A) 0.694 0.134 0.153 0.101 0.1 0.103 Calculated (mA/W) 5.9 1.1 1.3 0.9 0.9 0.9 Max Permissible (mA/W) n/a n/a 3.4 n/a 1.9 n/a
7th
8th
9th
10th
15th
39th
580
660
740
800
1140
3040
0.06 0.5 1
0.08 0.7 n/a
0.07 0.6 0.5
0.04 0.3 n/a
0.03 0.3 0.26
0.01 0.1 0.098
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