Download Rectifier Fundamentals Filtered Full Wave Bridge

Running Head: Filtered Full Wave Bridge Rectifier – Part II
Rectifier Fundamentals
Filtered Full Wave Bridge Rectifier
Part II – Impact of Load Impedance on Ripple Voltage
In this lab you will build circuits used to convert alternating current to pulsating direct current
using semiconductor diodes.
In this section we will look at a full wave bridge rectifier circuit with a capacitor (called a filter
capacitor) used to smooth out the pulsating direct current created by our rectifier circuit. We will
observe how the size of the load impedance affects the ripple voltage across the load (and current
through it).
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Filtered Full Wave Bridge Rectifier – Part II
Document content developed by:
Alexander McGlashan
Niagara College of Applied Arts and Technology
School of Technology, Department of Photonics
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Filtered Full Wave Bridge Rectifier – Part II
Purpose
In this section we will look at a full wave bridge rectifier circuit with a capacitor (called a filter
capacitor) used to smooth out the pulsating direct current created by our rectifier circuit.
Parts Required:
1 – 15kΩ resistor
4 – 1N400x rectifier diodes
Part II – Impact of Load Impedance on Ripple Voltage
As the size of the capacitor is increased, (and load impedance remains constant) the RC
discharge time increases. This results in a reduced ripple voltage (smoother load current).
1. In multisim open a new NI myDAQ design (or your saved design from Part I)
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Filtered Full Wave Bridge Rectifier – Part II
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2. Create the following full wave bridge rectifier circuit in multisim:
AI 0 is our source
AO 0 Channel 0 (scope)
AO 1 Channel 1 (scope)
Note that oscilloscope channels are frequently grounded together. With such an
oscilloscope we would have to measure the two signals independently with one channel
(one at a time). The myDAQ allows us to measure both signals at the same time.
3. Create the following table in your log book:
Load Resistor
15kΩ
Simulated Values
V(Ripple) p-p
I(Ripple) p-p
Open Load (no
resistor)
4. Open the function generator and oscilloscope.
 Set the frequency to 60Hz
 Set the amplitude to 10Vpp
 Select the Sine waveform
Real Values
V(Ripple) p-p
I(Ripple) p-p
Filtered Full Wave Bridge Rectifier – Part II
5. Run the simulation and adjust the scope settings such that one cycle of the source is
clearly visible.
Note that for Channel 1 we have set the Vertical Position to -5V and the Scale to
500mV/Div in order to zoom in on the ripple voltage.
6. Perform the following and record in your log book:
 Measure and compare the frequency of Channel 0 and Channel 1
 Measure the peak to peak voltage of Channel 1. This is the ripple voltage across
the load (V(Ripple) p-p)
 Calculate the variation in load current (I(Ripple) p-p)
7. Construct the real circuit and connect your myDAQ as configured in the simulation.
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Filtered Full Wave Bridge Rectifier – Part II
8. Make sure the Instrument Control for both the generator and scope are set to myDAQ
(not simulate). Run the circuit and compare to your simulation.
Record in your logbook:
 Measure the peak to peak voltage of Channel 1. This is the ripple voltage across
the load (V(Ripple) p-p)
 Calculate the variation in load current (I(Ripple) p-p)
9. In the simulation, change the load resistor R1 to a 10kΩ resistor.
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Filtered Full Wave Bridge Rectifier – Part II
10. Rerun the simulation
Record in your log book:
 Measure the peak to peak voltage of Channel 1. This is the ripple voltage across
the load (V(Ripple) p-p)
 Calculate the variation in load current (I(Ripple) p-p)
11. In the real circuit, replace the load resistor R1 with a 10kΩ resistor.
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Filtered Full Wave Bridge Rectifier – Part II
12. Run the circuit and compare to your simulation.
Record in your log book:
 Measure the peak to peak voltage of Channel 1. This is the ripple voltage across
the load (V(Ripple) p-p)
 Calculate the variation in load current (I(Ripple) p-p)
13. In the simulation, change the load resistor R1 to a 2.2 kΩ resistor.
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Filtered Full Wave Bridge Rectifier – Part II
14. Rerun the simulation
Record in your log book:
 Measure the peak to peak voltage of Channel 1. This is the ripple voltage across
the load (V(Ripple) p-p)
 Calculate the variation in load current (I(Ripple) p-p)
15. In the real circuit, replace the load resistor R1 with a 2.2 kΩ resistor.
16. Run the circuit and compare to your simulation.
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Filtered Full Wave Bridge Rectifier – Part II
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Record in your log book:
 Measure the peak to peak voltage of Channel 1. This is the ripple voltage across
the load (V(Ripple) p-p)
 Calculate the variation in load current (I(Ripple) p-p)
17. Create the following table in your log book:
V(Ripple) p-p
(After Approx. 30sec)
V(Load) peak
V(Source) peak
VFmax (Diode)
Calculate from
Results
Open Load Simulated
Open Load Real
18. In the simulation, remove the load resistor R1 (creating an open load or “unloaded”
condition).
19. Rerun the simulation
Observe that as time progresses the voltage across the capacitor approaches the
theoretical maximum voltage (note that the maximum voltage in our example is greater
than the normally cited value of source voltage less 1.4V for the diode voltage drops.
Typically a load resistor is continually drawing current from the source and capacitor
preventing this action from occurring.
In our example the current is so low that the forward voltage drop across each resistor (in
the simulation) is closer to 150mV instead of the typical 700mV.
Filtered Full Wave Bridge Rectifier – Part II
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Record your results in the table.
20. In the real circuit, remove the load resistor R1 and confirm the results of the simulation.
You may find that the voltage across the capacitor is lower in the real circuit.
 Record your results in the table
21. Explain the effect of load impedance on ripple voltage across the load. What creates a
more stable load voltage and current, a large resistor or a small one? Explain.
Expected Results
Load Resistor
15kΩ
10kΩ
2.2kΩ
Simulated Values
V(Ripple) p-p
1.268 Vp-p
1.659 Vp-p
3.161 Vp-p
V(Ripple) p-p
I(Ripple) p-p
84.53 uAp-p
165.9 uAp-p
1437 uAp-p
V(Load) peak
Real Values
V(Ripple) p-p
1.283 Vp-p
1.667 Vp-p
2.083 Vp-p
V(Source) peak
440 uVp-p
60 mVp-p
VFmax (Diode)
Calculate from
Results
(After Approx. 30sec)
Open Load Simulated
Open Load Real
I(Ripple) p-p
85.53 uAp-p
166.7 uAp-p
946.8 uAp-p
4.67 Vp-p
4.16 Vp-p
5.00 Vp-p
5.00 Vp-p
165 mV
420 mV