Examcrazy Logo
HOME  SITEMAP CONTACT US LOGIN
HOME Engineering AIEEE GATE IES DRDO-SET BSNL-JTO
MBA in India CAT How to Prepare for Exams Technical Freshers Jobs
  Follow us|  twitter  Orkut  facebook
Diode Tutorials
   Ideal Diodes
   Applications of Diodes
   Physical Operation of Diodes
   DC Analysis of Diode Circuits
   Small-Signal Diode Model and Its Application
   Zener Diodes
   Diode Rectifier Circuits (Half Cycle, Full Cycle, and Bridge)
   Peak Rectifiers
   Limiting and Clamping Diode Circuits. Voltage Doubler. Special Diode Types
Free Electronics Tutorials
   Diode Tutorials
   BJT Tutorials
   MOSFET Tutorials
   Electronics II Tutorials
   Applied Electromagnetics Tutorials
   Microwave Tutorials
GATE preparation tips
   GATE Books & How to prepare
   Objective Solving Tricks
   Other GATE links
   IES exam preparation
   All about DRDO-SET
More Engineering Links
   Directory of coaching Institutes
   Govt engg college rankings
   Private engg college rankings
   Admission notifications for Mtech/PhD
   All Engineering Colleges in India
Peak Rectifiers

The output of the rectifier circuits discussed in the last lecture is pulsating significantly with time. Hence, it’s not useful as the output from a DC power supply.
One way to reduce this ripple is to use a filtering capacitor. Consider the half-cycle rectifier again, but now add a capacitor in parallel with the load:

We expect that as soon as we turn on the source, the capacitor will charge up on “+” cycles of vI and discharge on the “-” cycles.
To smooth out the voltage, we need this discharge to occur slowly in time. This means we need to choose C large enough to make this happen, presuming that R is a given quantity (the Thévenin resistance of the rest of the circuit). The output voltage vO will then be a smoothed-out signal that pulsates with time:

Notice the diode current and the capacitor voltage. They display behavior much different than what one would find in an AC circuit.
Analysis of Peak Rectifier Circuits
We’ll require that RC T ō= , which means that the time constant of the RC circuit must be much greater that the period
of the input sinusoidal signal:

Now, our quest is to approximately determine the ripple voltage
vrassuming t>>T

When D is off, and assuming it is an ideal diode

[If D is not ideal then v0(t)~(v0-0.7)e-t/r.]
At the end of the discharge time, td, the output voltage equals

Substituting for vO from (1) at this time td leads to

This equation has the two unknowns Vr and td, assuming ō isknown. If we can determine td, then we can find Vr. Finding tdcan be done numerically by equating (1) to the expression forthe input voltage

and solving for the time td when the two are equal as

This needs to be done numerically since (5) is a “transcendentalequation.”Alternatively, if Ät is small compared to T (true when T ō , asassumed), then from (3)

Again, because T ō then we can truncate the series expansionof the exponential function to two terms (see Lecture 4) giving

This simple equation gives the ratio of the ripple voltage to the peak voltage of the input sinusoidal signal for the half-cyclerectifier. It’s worth memorizing, or knowing how to derive.Often R and T are fixed quantities. So from (7)

to obtain a small ripple voltage we need a large C in this case.
Conduction Interval
Lastly, the conduction interval Ät is defined as the time intervalin which the diode is actually conducting current. This timeperiod is sketched in the preceding two figures. The diode conducts current beginning at time td and ending at T,within each period. Using equation (4) at time td

We expect the conduction interval to be small. So truncating theseries expansion of cosine to two terms, (9) gives

The factor t łÄ is sometimes called the conduction angle, č. For Vr Vp this conduction angle (and conduction interval) will besmall, as expected.
Discussion
To reiterate, the objective of the peak rectifier is to charge theshunt C when D is on, and slowly discharge it during thosetimes when D is off.When does D conduct? During the Ät periods in the previousfigure. Also seeNote that this peak rectifier is not a linear circuit. iD is a very complicated waveform and not a sinusoid, as seen earlier in
There are no simple exact formulas for the solution tothis problem. The text only shows approximate solutions for peak iD:

Example N8.1 (similar to text example 3.9). A half-cycle peakrectifier with R = 10 kŁ is fed by a 60-Hz sinusoidal voltagewith a peak amplitude of 100 V.(a) Determine C for a ripple voltage of 2 Vpp. From (8):
or c=83.3uf
For a “factor of safety” of two, make C twice as large. Remember, a bigger C translates to smaller ripple. (b) Determine the peak diode current. Using (11):

When specifying a diode for your circuit design, you would need to find one that could safely handle this amount of current.Example N8.2. A half-cycle peak rectifier with R = 10 kŁ is fedby a 60-Hz triangula voltage with a peak amplitude of 100 V.

(a) Determine C for a ripple voltage of 2 Vpp. If you go back and look at the derivation of (8) you’ll find that there were no approximations made that required a sinusoidal waveform. Consequently, (8) applies to this triangular waveform as well, provided T ō . Hence, as before 83.3 C = ģF. (b) Determine the diode conduction time, Ät. Referring to this sketch of the region near the positive peak voltage for vI:

Because the rising portion of the waveform is a straight line:

To find Ät, equate

Therefore, for a triangular waveform

In this particular case,

Compare this time to a sinusoidal waveform:

This time is much longer than for the triangular waveform. Consequently, we would expect max D i for D to be much larger for the triangular waveform than for the sinusoid!
Full-Cycle Peak Rectifiers
In a similar fashion, we can also add a shunt C to full cycle and bridge rectifiers to convert them to peak rectifiers. For example, for a full-cycle peak rectifier:

The output voltage has less ripple than from a half-cycle peakrectifier (actually one half less ripple).

The “ripple frequency” is twice that of a half-cycle peak rectifier. Using the same derivation procedure as before with thehalf cycle, but with 2 T T . gives from (7)

Lastly, it can be shown that the id|max for the full-cycle peakrectifier:

is approximately one-half that of the half-cycle peak rectifierwhen Vr V p .


Discuss about DIODE here
   START NEW THREADS
Discussion Board for DIODE
You can discuss all your issues on DIODE here
Thread / Thread Starter Last Post Replies Views
Type of diode
I need short notes for all type of diode.


Posted By :-
 imteyaz86
Oct 27, 11:50:24 AM 0 5941
signals and system
hi i am venkatesh which author use in signal and system for gate


Posted By :-
 venkatesh.dace2
Oct 13, 4:38:08 PM 0 5623
Thank u
i need some links to download free ebooks multiple choice for my gate preparation - V.Vivek Sharma.


Posted By :-
 vvivekxp@yahoo.com
Oct 4, 9:56:42 AM 0 4035
study materials
i want to study materials of digital communication.


Posted By :-
 titon
Feb 6, 3:43:05 PM 4 11285
More examples of non linear circuit analysis
Notes are very simple to understand the concepts.


Posted By :-
 ruby2810
Sep 9, 3:17:49 PM 0 8410
study materials
can i get some study materials by online


Posted By :-
 shyama.km
Sep 4, 9:05:49 AM 0 5630
hiii plz give me basic information about electromegnetics
i have a dout between combination of electrostatics and megnetostatics


Posted By :-
 pandya.saga
Jul 29, 2:38:13 PM 0 4336
hi
pls send me a link on answered problems on electronic devices and circuit theory by boylestad and nashelsky.. ty


Posted By :-
 flux089
Jul 25, 11:21:28 PM 0 4832
electronics and communication
i am in 4th year


Posted By :-
 gauravjai24.ece.uit@gmail.com
Jun 10, 6:02:44 AM 0 4699
bjt
about bipolar device


Posted By :-
 vikashgupta160489
Feb 13, 2:11:36 PM 2 9723
h parameters of transister
i want h parameters of transister


Posted By :-
 vijaybaviskar007
Feb 11, 7:52:45 AM 3 14587
very good tutorials
the explanations r very easy to understand


Posted By :-
 blues2torn@rediffmail.com
Dec 7, 8:38:09 PM 0 4816
ECE
the explanation was nice...more of these explanations on other topics would be of much help and is expected urgently...


Posted By :-
 pallavi.sist@gmail.com
Dec 2, 10:32:29 PM 0 5142
e.d.c
i want to simple way abt all the diode n jfet


Posted By :-
 vijayjyani@gmail.com
Jun 4, 10:25:28 AM 1 7099
Thanks for nice tutorials
Thanks for nice tutorials


Posted By :-
 my.gateprep
Nov 26, 8:29:06 AM 0 4767

To start your new thread you must login here.
New user signup at ExamCrazy.com Exam Crazy
To reply/post a comment you need to login, Use your user name and password to login if you are already registered else register here

EXISTING USER LOGIN
(Members Login)
Username:
Password:
NEW USER REGISTERATION FORM
Login-Id
Email-ID
Password
Confirm-Password
Full-Name

  About us | Privacy Policy | Terms and Conditions | Contact us | Email: support@Examcrazy.com  
Copyright © 2014 Extreme Testing House, India. All rights reserved.  1212