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
DC Analysis of Diode Circuits

We’ll now move on to the DC analysis of diode circuits. Let’s consider this very simple diode circuit:

We will assume that the diode is forward biased. Using KVL VDD=IR+VD From the characteristic equation for the diode

Assuming n, IS, and VT are known, we have two equations for the two unknown quantities VD and I. Substituting (2) into (1):

which is a transcendental equation for VD. There is no simple analytical solution to this equation. So how do we solve such a circuit problem? Over the next couple of pages we’ll mention five methods.
1. Graphical Analysis. Begin with the diode i-v characteristic curve:

2.
From (1), we can rearrange the equation in terms of I to also plot above. That is, from (1)

which is an equation for a straight line ( y b mx = + ):

We call this straight line the load line.
Now, plot both of these curves on the same graph:

The point where these two curves intersect is the simultaneous solution to the two equations (1) and (2). This graphical method is an impractical solution method for all but the simplest circuits. However, it is useful for a qualitative understanding of these circuits. For example, what happens when:
(a) VDD increases?

(b) R increases?
(c)
3. Simulation packages. SPICE, Agilent’s Advanced Design System (ADS), etc. Here is a simple example using ADS:
4.
3. Numerical methods. Use Mathematica, Matlab, Mathcad, etc.
Here is a simple example from Mathcad:

4. Iterative analysis. See example 3.4 in the text.
5. Approximate analysis. This is by far the most widely used approach for hand calculations.
Approximate Diode Circuit Solutions
There is often a need for us to perform design with pencil and paper. Remember: simulation packages don’t design for you, they only analyze circuits. There’s a big difference between design and analysis!
There are two very important approximate diode models that allow easier paper designs:
1. Constant-Voltage-Drop (CVD) Model.
2. Piecewise Linear (PWL) Model.

Constant-Voltage-Drop (CVD) Model In this model, the characteristic curve is approximated as:


In words, this model says that if the diode is forward biased, then the voltage drop across the diode is VD. If not forward biased, the diode is then reversed biased and the current is zero and VD can be any value < VD.
VD is often set to 0.7 V for silicon diodes, as shown above, while set to 0.2 V for Schottky diodes, for example. The CVD circuit model for diodes is

This is probably the most commonly used diode model for hand calculations.
Example N3.1. Determine the current I in the circuit below using the CVD model and assuming a silicon diode.

Using the CVD model, the equivalent approximate circuit is:


Assuming the diode is forward conducting (i.e., “on”) with VD = 0.7 V and using KVL in this circuit:

The positive value of this current indicates our original assumption that the diode is “on” is correct.

Since I is negative, then D must be reversed biased. This means our initial forward conducting assumption was incorrect. Rather, in this situation I = 0 and VD = 0.5 V.

Piecewise Linear (PWL) Diode Model

This is a “battery plus internal diode resistance model.” It is one step better than the CVD model by incorporating a slope to the interpolative line:

The finite slope to this curve means that the diode has a nonzero internal resistance, which we will label as rD. The equivalent circuit for the PWL diode model is then


Example N3.2. Determine the current I in the circuit below using the PWL diode model shown in text Figure.
From Fig., we can determine VD0 and rD for the particular diode whose characteristic equation is shown:


The equivalent circuit using the PWL model of the diode is then


Assuming the diode is “on,”, then by KVL:
This is close to the 1.3 mA we computed in the last example using the cruder CVD model. Again, the positive value of this current indicates that we made the correct choice that the diode is “on.”
What’s the forward voltage drop across the diode?

Is this enough to turn the diode on? Yes, referring to the equivalent circuit above



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 5778
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 5471
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 3906
study materials
i want to study materials of digital communication.


Posted By :-
 titon
Feb 6, 3:43:05 PM 4 10970
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 8130
study materials
can i get some study materials by online


Posted By :-
 shyama.km
Sep 4, 9:05:49 AM 0 5484
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 4210
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 4696
electronics and communication
i am in 4th year


Posted By :-
 gauravjai24.ece.uit@gmail.com
Jun 10, 6:02:44 AM 0 4565
bjt
about bipolar device


Posted By :-
 vikashgupta160489
Feb 13, 2:11:36 PM 2 9469
h parameters of transister
i want h parameters of transister


Posted By :-
 vijaybaviskar007
Feb 11, 7:52:45 AM 3 14251
very good tutorials
the explanations r very easy to understand


Posted By :-
 blues2torn@rediffmail.com
Dec 7, 8:38:09 PM 0 4696
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 5018
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 6920
Thanks for nice tutorials
Thanks for nice tutorials


Posted By :-
 my.gateprep
Nov 26, 8:29:06 AM 0 4631

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.  170