Running Head: Filtered Full Wave Bridge Rectifier – Part I
Rectifier Fundamentals
Filtered Full Wave Bridge Rectifier
Part I – Impact of Filter Capacitance 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 capacitor affects the ripple voltage across the load (and current
through it).
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Filtered Full Wave Bridge Rectifier – Part I
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 I
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
1 – 1uF, 10uF, 100uF capacitors
Part 1 – Filter Capacitor Impact 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
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Filtered Full Wave Bridge Rectifier – Part I
2. Create the following full wave bridge rectifier circuit in multisim:
3. Wire inputs AI 0 across output AO 0 (measuring our source voltage with Channel 0) and
AI 1 across the load resistor (measuring the load voltage with Channel 1).
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.
4. Open the function generator and oscilloscope.
 Set the frequency to 60Hz
 Set the amplitude to 10Vpp
 Select the Sine waveform
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Filtered Full Wave Bridge Rectifier – Part I
5. Run the simulation and adjust the scope settings such that one cycle of the source is
clearly visible.
6. Perform the following
 Measure and compare the frequency of Channel 0 and Channel 1
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Filtered Full Wave Bridge Rectifier – Part I



Measure the peak to peak voltage of Channel 1. This is the ripple voltage across
the load (V(Ripple) p-p)
Measure the peak voltage of Channel 1
Calculate the peak load current
7. Construct the real circuit and connect your myDAQ as configured in the simulation.
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.

Using the scope Log function (located in lower right corner of the scope
instrument panel) save your data
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Filtered Full Wave Bridge Rectifier – Part I
9. In the simulation, connect a 1uF capacitor in parallel with the load resistor R1.
10. Rerun the simulation



Measure the peak to peak voltage of Channel 1.
Measure the peak voltage of Channel 1
Calculate the peak load current
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Filtered Full Wave Bridge Rectifier – Part I
11. In the real circuit, place a 1uF capacitor in parallel with the load resistor R1.
12. Run the circuit and compare to your simulation.

Using the scope Log function (located in lower right corner of the scope
instrument panel) save your data
13. In the simulation replace the 1uF capacitor with a 10uF capacitor and rerun the
simulation.
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Filtered Full Wave Bridge Rectifier – Part I



Measure the peak to peak voltage of Channel 1.
Measure the peak voltage of Channel 1
Calculate the peak load current
14. In the real circuit, replace the 1uF capacitor with a 10uF capacitor.
15. Run the circuit and compare to your simulation.

Using the scope Log function (located in lower right corner of the scope
instrument panel) save your data
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Filtered Full Wave Bridge Rectifier – Part I
16. In the simulation replace the 10uF capacitor with a 100uF capacitor and rerun the
simulation.



Measure the peak to peak voltage of Channel 1.
Measure the peak voltage of Channel 1
Calculate the peak load current
17. In the real circuit, replace the 10uF capacitor with a 100uF capacitor.
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Filtered Full Wave Bridge Rectifier – Part I
18. Run the circuit and compare to your simulation.

Using the scope Log function (located in lower right corner of the scope
instrument panel) save your data
19. Press Stop on the generator. Carefully watch the scope screen as you press Run on the
generator. You should notice that for the first several cycles the source waveform
becomes distorted, and the load voltage is less than expected.
It is during this period that the circuit is experiencing “surge current” where the capacitor
presents an extremely low impedance as it attempts to charge itself from a nearly
completely discharged state.
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Filtered Full Wave Bridge Rectifier – Part I
By increasing the size of the capacitor, not only have we increased the discharge time
(smoothing the load voltage and current), we have also increased the charge time making
it easier to see the surge current in action.
During this time the circuit current exceeds the capability of the myDAQ (resulting in the
distorted source voltage). It is important to take surge current into account when
designing a power supply, so that you do not exceed the maximum current capacities of
other elements in the supply such as the rectifier diodes.
We will see this effect in Part II - Impact of Load Impedance on Filtering as well.
20. Explain the effect of capacitor size on ripple voltage across the load. What creates a more
stable load voltage and current, a large capacitor or a small one? Explain.
21. Explain the effect of capacitor size on surge current. What is the danger of surge current?
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