Understanding Diodes: Structure, Characteristics, and Applications in Circuits, Slides of Electronics

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Chapter 3 – Diodes

Introduction

http://engr.calvin.edu/PRibeiro_WEBPAGE/courses/engr311/311_frames.html

The ideal diode: (a) diode circuit symbol; (b) i-v characteristic; (c) equivalent circuit in the reverse direction; (d) equivalent circuit in the forward direction.

The Ideal Diode

The i-v characteristic of a silicon junction diode.

Diode – i-v Characteristic

The diode i-v relationship with some scales expanded and others compressed in order to reveal details.

Diode – i-v Characteristic

(a) The pn junction with no applied voltage (open-circuited terminals). (b) The potential distribution along an axis perpendicular to the junction.

Diode – Physical Structure

The pn junction excited by a constant-current source I in the reverse direction. To avoid breakdown, I is kept smaller than Is. Note that the depletion layer widens and the barrier voltage increases by Vr volts, which appears between the terminals as a reverse voltage.

Diode – Physical Structure

The pn junction excited by a constant-current source supplying a current I in the forward direction. The depletion layer narrows and the barrier voltage decreases by V volts, which appears as an external voltage in the forward direction.

Minority-carrier distribution in a forward-biased pn junction. It is assumed that the p region is more heavily doped than the n region; NA  ND.

Fig. 3.19 Graphical analysis of the circuit in Fig. 3.18.

Fig. 3. 20 Approximating the diode forward characteristic with two straight lines.

Fig. 3.23 Development of the constant-voltage-drop model of the diode forward characteristics. A vertical straight line (b) is used to approximate the fast-rising exponential.

Fig. 3. 24 The constant-voltage-drop model of the diode forward characteristic and its equivalent circuit representation.

Fig. 3. 26 Equivalent circuit model for the diode for small changes around bias point Q. The incremental resistance rd is the inverse of the slope of the tangent at Q , and VD 0 is the intercept of the tangent on the vD axis (see Fig. 3. 25 ).

Fig. 3.27 The analysis of the circuit in (a), which contains both dc and signal quantities, can be performed by replacing the diode with the model of Fig. 3.26, as shown in (b). This allows separating the dc analysis [the circuit in (c)] from the signal analysis [the circuit in (d)].