This document discusses diode equivalent circuit models, which are used to approximate the nonlinear behavior of real diodes for circuit analysis purposes. It describes three common diode models: the ideal diode model, which represents a diode as a simple switch; the practical (or simplified) model, which includes a 0.7V voltage drop; and the piecewise linear model, which approximates the diode curve as a series of linear segments. The document explains that diode models allow the use of conventional linear circuit analysis by replacing the nonlinear diode with an equivalent linear circuit representation.

1. Diode Equivalent Circuits/
Diode Models
Dr.G.Puvaneswari
Assistant Professor(SG)
ECE, Coimbatore Institute of
Technology, Coimbatore

2. Diode Equivalent Circuits/Diode
Models
• It is a combination of elements that
represents the actual terminal characteristics
of a device in its operating region
• Diode models are the mathematical models
used to approximate the actual behavior of
real diodes for analysis purpose.
• The diode circuits are solved by using diode
models in the place of diodes without
affecting the system behavior

3. Why diode models
• Diode’s V-I characteristics is nonlinear
• nonlinearity complicates the calculations in
circuits involving diodes
• Use of diode models or equivalent circuits
enables the use of conventional circuit
analysis techniques

4. Diode Models
• Three models are used
–Ideal Diode Model
–Simplified
–Piecewise linear model

5. Ideal diode model
• It is the least accurate approximation
• It is represented by a simple switch
• An ideal forward-biased diode acts like a closed (on)
switch
• An ideal reversed-biased diode acts like an open (off)
switch
• The barrier potential, the forward dynamic resistance,
and the reverse current are neglected
• Diode is replaced by simple switch
• These models are used in troubleshooting, to
determine whether the diode is working properly and
where the exact values of voltage or current are not
needed

7. Simplified diode model/Practical
diode model
• The practical model includes the barrier
potential
• It states that a forward-biased silicon diode
under dc condition has a voltage drop (cut-in
voltage) of 0.7 V (for Si diodes) across it at any
level of diode current within the rated values
• It consists of a voltage source representing the
cut-in voltage of the diode and an ideal diode
acting as a switch

8. Simplified equivalent circuit

9. Circuit with ideal diode

10. Forward bias
• forward current is determined as follows by
applying Kirchhoff’s voltage law

11. Reverse bias
• diode is assumed to have zero reverse current

12. Piecewise model
• This model approximates the characteristics of the
device by straight-line segments
• But straight-line segments do not result in an exact
duplication of the actual characteristics, especially in
the knee region
• This model approximates the diode characteristic
curve as a series of linear segments
• In mathematics, piecewise means taking a function
and breaking it down into several linear segments

13. Piecewise Approximation

14. • This model contains a voltage source representing
the cut-in voltage and diode resistance (rav)
• Battery (0.7V) specifies the voltage across the device
must be greater than the threshold battery voltage
before conduction through the device in the
direction
• When conduction is established the resistance of the
diode is the specified value of rav.

15. • approximate level of rav can be determined
from a specified operating point on the
specification sheet
• For a silicon semiconductor diode, if IF =10 mA
at VD =0.8 V, for silicon that a shift of 0.7 V is
required before the characteristics rise

16. Summary

17. References
• Robert L. Boylestead and Louis Nasheresky
"Electron Devices and Circuits: Theory and
Practice", Prentice Hall of India, 11th Edition,
2013.
• “Fundamentals of Analog Circuits” by Thomas
Floyd