Transcript Full wave rectifier

C. K. Pithawalla College Of Engineering
And Technology.
Subject: Electronic Devices And Circuits
Topic: Rectifiers
Prepared by(Group no. 3):
1.
2.
3.
4.
5.
Bharuchwala Zainab-140090111006
Sadriwala sherebanu-140090111050
Parekh Janki-140090111033
Rathod Axay-1511909
Kakadiya Kartik-1511915
Rectification:
Rectification is the process of converting the alternating
voltage or current into the corresponding direct(dc)quantity.
•
• The input to a rectifier is ac whereas its output is
undirectional or dc.
• The electronic circuit which carries out rectification is called
as rectifier.
Rectifiers:
Rectifier is an electronic device which is used or converting
an alternating(ac) voltage or current into unidirectional(dc)
voltage or current.
Operation:
• The basic building blocks of regulated power supply are:
1. A step down transformer
2. A rectifier
3. Filter
4. A voltage regulator
• A step down transformer is used to reduce the ac mains voltage to
an adequately small voltage.
• This voltage is converted into a pulsating dc voltage by the
rectifier.
• The pulsating dc voltage at the rectifier output is converted into a
ripple free steady dc voltage by the filter circuit.
• The filtered dc voltage is then applied to a voltage regulator which
tries to keep the dc output voltage constant even if the supply
voltage fluctuations take place.
Classification of rectifiers:
Rectifier
circuits
Full wave
rectifier(FWR)
FWR with
center trapped
transformer
Half wave
rectifier(HWR
)
Full wave
bridge rectifier
Half wave rectifier(HWR):
In half wave rectifier, the rectifier is the only during one half
cycle of the ac supply.
•
•So output is produced only in that half cycle. The output is
suppressed in the other half cycle.
• The conduction takes place only in one half cycle of supply,
hence the name of this circuit is half wave rectifier.
Rectifier circuit:
Wave form for half wave positive half cycle:
Where:
Vdc, Vav - the DC or average output voltage,
Vpeak, the peak value of the phase input voltages,
Vrms, the root-mean-square value of output voltage.
Voltage regulation for HWR:
Where, Vnl = average load voltage at no load
Vfl = average load voltage at full load
Ideally the load regulation should be 0% and practically
it should be as low as possible .
Rectification Efficiency:
Ideally the conversion efficiency should be 100% and practically it
should be as high as possible.
Transformer Utilization Factor:
Disadvantages:
• Due to the unidirectional current flow through the transformer, there is a
possibility of core saturation. To avoid it, transformer size must be increased.
• Ripple factor is high(1.21)
• Larger filter components are required.
Avantages :
• Simple construction.
• Less number of components are required to be used.
• Small size.
Applications:
• In the eliminators for pocket radios or eliminators for walkman or in the low
cost power supply.
Full wave rectifier:
A full-wave rectifier converts the whole of the input waveform to one of
constant polarity (positive or negative) at its output. Full-wave rectification
converts both polarities of the input waveform to pulsating DC (direct
current), and yields a higher average output voltage. Two diodes and
a center tapped transformer, or four diodes in a bridge configuration and
any AC source (including a transformer without center tap), are needed.
Waveforms for full wave rectifier:
The average and root-mean-square no-load output voltages of an ideal single-phase full-wave
rectifier are:
Voltage Regulation:
Rectification efficiency:
The maximum efficiency of a Full Wave Rectifier is 81.2%.
Transformer Utilization Factor
Transformer Utilization Factor, TUF can be used to determine the rating of a
transformer secondary. It is determined by considering
the primary and the secondary winding separately and it gives a value of 0.693.
Disadvantages:
• Since PIV of the diodes is 2 Vm size of the diodes is larger and they are more costly.
• Cost of the center taped transformer is high.
Advantages:
• Low ripple factor as compared to HWR.
• Better rectification efficiency.
• No possibility of transformer core saturation.
Applications:
• Laboratory power supplies.
• High current power supplies.
• Battery charges.
• power supplies for various electronic circuits.
Full wave rectifier with centre taped transformer:
In the case of centre-tap full wave rectifier, only two diodes are used, and
are connected to the opposite ends of a centre-tapped secondary
transformer as shown in the figure below. The centre-tap is usually
considered as the ground point or the zero voltage reference point.
Bridge Rectifier:
• The disadvantages of the full wave rectifier such as high PIV and
compulsory use of center tapped transformer are overcome in the bridge
rectifier.
• A bridge rectifier uses 4 diodes that are connected in the form of a
Wheatstone’s bridge. In a single half cycle only two diodes conduct.
Consider the circuit diagram given below.
Waveform for Bridge rectifier:
Disadvantages:
• The number of diodes used is four instead of two for FWR.
• As two diodes conduct simuntaneously , the voltage drop increases and the
output voltage reduces.
Advantages:
• It requires a small size transformer. Centre tap transformer is not required.
This makes the bridge rectifier cost effective.
• High average output voltage.
Applications:
• Laboratory dc power supplies.
• High current power supplies.
• Battery charger.
• DC power supplies for various electronics circuits
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