3.1) The Ideal Diode

전자회로 I

Chapter 3

Diodes

3.1) The Ideal Diode

Current-Voltage Characteristic

Figure 3.1 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.

Chapter 3

Lecture Homepage : http://signal.korea.ac.kr

Signal Processing Lab., http://signal.korea.ac.kr Dept. of Elec. and Info. Engr., Korea Univ.

2016년 6월 27일 4 pages

3.1) The Ideal Diode

Current-Voltage Characteristic

Figure 3.2 The two modes of operation of ideal diodes and the use of an external circuit to limit the forward current (a) and the reverse voltage (b).

3.1) The Ideal Diode

A Simple Application : The Rectifier

Figure 3.3 (a) Rectifier circuit. (b) Input waveform. (c) Equivalent circuit when v_I  0. (d) Equivalent circuit when v_I = 0. (e) Output waveform.

Chapter 3

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2016년 6월 27일 6 pages

3.1) The Ideal Diode

Another Application: Diode logic Gates

Figure 3.5 Diode logic gates: (a) OR gate; (b) AND gate (in a positive-logic system).

Y = A + B + C Y = A B C  

3.2) Terminal Characteristics of Junction Diodes

Figure 3.7 The i–v characteristic of a silicon junction diode.

Figure 3.8 The diode i–v relationship with some scales expanded and others compressed in order to reveal details.

Chapter 3

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2016년 6월 27일 8 pages

3.2) Terminal Characteristics of Junction Diodes The Forward-Bias Region

(3.1)

) 1 (



 I

e

i

 In the forward region the i - v relationship is closely approximated by

25mV V

of value the C) (20 re temperatu room

At

coulomb 10

1.60 charge

electronic of

magnitude the

q

C in re temperatu 273

kelvins in

re temperatu absolute

the T

vin joules/kel 10

1.38 constant s

Boltzmann' k

T

19 - -23

































(3.2)

q

V

 kT

 The voltage V_T in Eq. (3.1) is a constant called the thermal voltage and is given by

(3.3)

/V_T v S

e I i _

 For appreciable current I in the forward direction, specifically for I >> I_S, Eq. (3.1) can be approximated by the exponential relationship

3.2) Terminal Characteristics of Junction Diodes The Forward-Bias Region

(3.4)

ln

S

T

I

V i v 

 This relationship can be expressed alternatively in the logarithmic form

VT

V

e

I

I

1

2



VT

V S

e I

I

_

VT

V S

e I

I

_

 Let us consider the forward i – v relationship in Eq. (3.3) and evaluate the current I₁ corresponding to a diode voltage V₁ :

 Similarly, if the voltage is V₂, the diode current I₂ will be

 These two equations can be combined to produce

1 2 1

2

ln

I V I

V

V _{ }

Chapter 3

Lecture Homepage : http://signal.korea.ac.kr

Signal Processing Lab., http://signal.korea.ac.kr Dept. of Elec. and Info. Engr., Korea Univ.

2016년 6월 27일 10 pages

3.2) Terminal Characteristics of Junction Diodes The Forward-Bias Region

Figure 3.9 Illustrating the temperature dependence of the diode forward characteristic. At a constant current, the voltage drop decreases by approximately 2 mV for every 1C increase in temperature.

3.2) Terminal Characteristics of Junction Diodes The Reverse-Bias Region

I

i  

 The reverse-bias region of operation is entered when the diode voltage v is made negative. Equation (3.1) predicts that if v is negative and a few times larger than V_T (25mV) in magnitude, the exponential term becomes negligibly small compared to unity, and the diode current becomes

• That is, the current in the reverse direction is constant and equal to I_S. This constancy is the reason behind the term saturation current.