diodes 1. basic diode concept. 2. load-line analysis of diode circuit. 3. zener-diode voltage...
TRANSCRIPT
Diodes
1. Basic diode concept.
2. Load-line analysis of diode circuit.
3. Zener-diode voltage regulator circuit.
4. Ideal-diode model.
5. Applications of diodes.
BASIC DIODE CONCEPTS
A pn junction
Drift and diffusion currents in a pn junction
Figure 9.7
Forward- and reverse-biased pn junctions
Figure 9.8, 9.9
Semiconductor diode i-v characteristic
Semiconductor diode circuit symbol
Figure 9.10
The i-v characteristic of the semiconductor diode
Shockley Equation
1exp
T
DsD nV
vIi
q
kTVT
k = 1.38 × 10–23 J/K is Boltzmann’s constant and q = 1.60 × 10–19 C is the magnitude of the electrical charge of an electron. At atemperature of 300 K, we have mV 26TV
Exercise 10.1
At a temperature of 300K, a certain junction
diode has iD = 0.1mA for vD = 0.6V. Assume
that n is unity and use VT = 0.026V. find the
value of the saturation current Is.
1exp
T
DsD nV
vIi
A
nVv
iIs
TD
D
15
4
10502.9
1)026.0/6.0exp(10
1)/exp(
LOAD-LINE ANASYSIS OF DIODE CIRCUITS
LOAD-LINE ANALYSIS OF DIODE CIRCUITS
DDSS vRiV By applying KVL, we get
But two unknowns, we need one more equation relating iD and vD to solve the problem.
Example 10.1If the circuit of Figure 10.5 has Vss = 2V,
R = 1k, and a diode with the characteristic shown in Figure 10.7, find the diode voltage and current at the operating point.
Example 10.2Repeat Example 10.1 if Vss = 10V, R = 10k
Vss=10, R=10k
Vss = 2, R = 1k
Vss = i R + VD
ZENER-DIODE VOLTAGE-REGULATOR CIRCUITS
What is a Zener diode?
Zener Diodes
Diodes that are intended to operate in the breakdown region are called Zener diodes.
Breakdown
region
ZENER-DIODE VOLTAGE-REGULATOR
CIRCUITSA voltage regulator circuit provides a nearly constant voltage to a load from a variable source.
0 DDSS vRiV
Example 10.3
The voltage-regulator circuit of Figure 10.9
has R = 1k and use a Zener diode having the
characteristic shown in Figure 10.10. Find the
output voltage for Vss = 15V. Repeat for Vss =
20V.
R = 1k
Vss + i R +VD = 0i = 0, VD = -Vss
VD = 0, i = Vss/R
IDEAL-DIODE MODEL
IDEAL-DIODE MODEL
The ideal diode acts as a shortcircuit for forward currentsand as an open circuit withreverse voltage applied.
Figure 9.11
Large-signal on/off diode model
Figure 9.12, 9.13, 9.14
Circuit containing ideal diode Circuit of Figure 9.12, assuming that the ideal diode conducts
Figure 9.13
Circuit of Figure 9.12, assuming that the ideal diode does not conduct
Figure 9.14
Figure 9.15, 9.16, 9.17
Figure 9.17
Figure 9.16
Summary of Guidelines to analysis ideal-diode
circuits
APPLICATION OF DIODES
Figure 9.45
DC power supply
RECTIFIER CIRCUITS
Half-Wave Rectifier Circuits
Figure 9.20, 9.21
Ideal diode rectifier input and output voltages
As Vs reaches VB, then diode starts to conduct
r
L
V
TIC
2r
mL
VVV
Vr/ 2
Full-Wave Rectifier Circuits
Full-wave rectifier
Figure 9.42
Operation of bridge rectifier
Figure 9.49
(a) A Zener diode voltage regulator;
(b) (b) simplified circuit for Zener regulator