Basics of Rectifiers

1. Basic of Rectifiers
Rajesh B. Lohani
Dept. of E & TC
Goa College of Engineering
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References
Electronic Device Theory Robert Boylestead and Nashelsky
Electronic Devices and Circuits by Allan Mottershead
Integrated Electronics by Millman Halkias
Weber State University.
EMT212/4 – Analogue Electronic II
Courtesy : Google images
The presentation focus on the basics of rectifier.

2. Learning Objectives
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i) Understand the basic operation of rectifier circuits.
ii) Analyze the different types of rectifiers.

3.  A rectifier is a circuit which converts the Alternating Current
(AC) input power into a Direct Current (DC) output power.
 Diode and SCR are primarily used in rectifier circuits.

4. Difference between AC and DC signals.
AC (Alternating current) DC (Direct Current)
AC signal Flows one way, then
the other way, continually
reversing direction.
Direct Current signal
always flows in the same
direction, but it may
increase and decrease.
Continually changing between
positive (+) and negative (-).
A DC signal is always
positive (or always
negative), but it may
increase and decrease.
Rate of changing direction is
called the frequency of the AC
and it is measured in hertz (Hz).
Frequency is zero.
Average value of signal is zero. It will always have average
value.

5. step #1: increase / decrease rms magnitude
of AC wave using transformer
step #2: convert full-wave AC to half-wave
DC (still time-varying and periodic)
step #3: employ low-pass filter to reduce
ripple component by > 90%
step #4: employ voltage regulator to
eliminate ripple
step #5: supply dc load
.

6. The Half-Wave Rectifier
 Half-wave rectifier – has one
diode and utilizes only alternate
half-cycles of the input signal.
 Constant voltage drop model
is employed.
 What if for Small inputs?
 Regardless of the model employed,
one should note that the rectifier
will not operate properly when
input voltage is small (< 1V)
 Those cases require a precision
rectifier (diode with op amps).
PIV = Vm
Ripple frequency = 50 Hz

7. Full-Wave Rectifier
Center-tapping of the transformer
PIV = 2Vm
Ripple frequency = 100 Hz
6-0-6 means RMS value
6-0-6

8. Full-Wave Rectifier
When instantaneous source voltage is positive, D1
conducts while D2 blocks…
when instantaneous source voltage is negative, D2
conducts while D1 blocks

9.  An alternative implementation of the full-wave
rectifier is bridge rectifier
 Does not require center-tapped transformer
 Four diodes instead of two
Bridge Rectifier
PIV = Vm
Ripple frequency = 100 Hz

10. The Rectifier with a Filter Capacitor
 Filters are required to remove the ripple components so as to get
regulated dc output voltage free from unwanted ac components.
Why is this example unrealistic?
 Because for any practical application, the converter would supply a load
(which in turn provides a path for capacitor discharging)
The PIV for the above capacitor filter is 2Vm.
 Mainly passive components like Capacitors, Inductors
and their combination are used in filter circuits.

11. The Rectifier with a Filter Capacitor
with load

12. Relationship between
Peak-to-peak and rms
value.

14. Disadvantages of Half Wave Rectifier
•Ripple production is more
•Harmonics are generated
•Utilization of transformer is very low
•Efficiency of rectification is low
Advantages of Half Wave Rectifier
•Affordable
•Simple connections
•Easy to use as the connections are simple
•Number of components used are less
Applications of Half Wave Rectifier
•Power rectification
•Signal demodulation: for demodulating the AM signals.
•Signal peak detector: for detecting the peak of the incoming waveform.
Rectifier Efficiency
Rectifier efficiency is the ratio of output DC power to the
input AC power. For a half wave rectifier, rectifier
efficiency is 40.6%.
Half-waveRectifier:
Takeaways

15. Disadvantages of Full Wave Rectifier
Expensive and complicated circuit.
Advantages of Full Wave Rectifier
The rectifier efficiency of a full wave rectifier is
high (81.2%.)
The power loss is very low
Number of ripples generated are less
Applications of Full Wave Rectifier
1. For supplying polarized voltage in welding and for this bridge rectifiers are used.
2. For detecting amplitude of modulated radio signals.
Full-waveRectifier:
Takeaways

16. 16
Learning Outcomes
 The viewer will be able to classify the different
types of rectifiers.
 Assemble and test the rectifier circuits.
 Select rectifier circuit as per applications.
Constructive criticisms are welcome for further improvement.
You can reach me at: rblohani@gec.ac.in
This presentation has been peer-reviewed by Dr. Samarth Borkar.
Thanks to Mr. Pushpshil Satardekar for support.

17. Dedicated to my loving parents
Late. Janaki B. Lohani and Mr. Basant B. Lohani
(Retd. Principal)
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18. Thank You for your time.