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Diode Equivalent Circuit Models Explained
- 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
- 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
- 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