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ELECTRONIC DEVICESAssist. prof. Laura-Nicoleta IVANCIU, Ph.D.
C3 – DR switching circuits
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2Laura-Nicoleta IVANCIU, Electronic devices
vD < 0.7 V iD = 0
D – (off) D – (on)
vD < 0.7 V vD > 0.7 V
vD = 0.7 V iD > 0
C3 – DR switching circuits
T
D
nVv
SD eIi ≅
Constant voltage drop model
Exponential model
Previously on ED (C2):
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3Laura-Nicoleta IVANCIU, Electronic devices
C3 – DR switching circuits
Contents
Two-port DR networks. DR switching circuits. Voltage transfer characteristic (VTC) Two-port DR networks analysis Applications of two-port DR networks
Half-wave rectifier Pulses selector Voltage limiter Maximum multi-port networks Minimum multi-port networks
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4Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks. DR switching circuits.
Two-port network = circuit w/ two ports – input, output
Two-port DR network = DR circuit w/ two ports – input, output
Switching two-port DR network = DR circuit w/ two ports, D – (on), (off)
The analysis of switching two-port DR networks works with theconstant voltage drop model of the diode.
C3 – DR switching circuits
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5Laura-Nicoleta IVANCIU, Electronic devices
Voltage transfer characteristic
Voltage transfer characteristic (VTC)
graphical illustration of vO (vI)
C3 – DR switching circuits
Steps for deducing the VTC: Take into account all possible situations that result from the
combination of diode states (on, off) For each situation,
draw the equivalent circuitfind vOdetermine the range of vI
Plot the VTC.
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6Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks analysis
Deduce and plot VTC vO (vI)
C3 – DR switching circuits
Step 1. Write down KVL and Ohm’s law for the circuit (circuit’s equations)
Example
Step 2. Draw the equivalent circuits for D-(on) and D-(off)Step 3. Find vO and the range for vI by replacing the diode’s equations in the circuit’s equations. Step 4. Write down the complete expression of VTC vO (vI) and plot it, for D-(on) and D-(off).
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7Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks analysis
Deduce and plot VTC vO (vI)
C3 – DR switching circuits
Step 1. Write down KVL and Ohm’s law for the circuit (circuit’s equations)
Example
Rivvvv
DO
ODI
==++− 0
! Always valid, regardless of the state of the diode!
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8Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks analysisC3 – DR switching circuits
Step 2. Draw the equivalent circuits for D-(on) and D-(off)
Example
D – (off) D – (on)
Deduce and plot VTC vO (vI)
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9Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks analysisC3 – DR switching circuits
Step 3. Find vO and the range for vIby replacing the diode’s equations in the circuit’s equations.
Example
D – (off)
Deduce and plot VTC vO (vI)
Rivvvv
DO
ODI
==++− 0
0=Ov
OID vvv −=
V7.0<Iv
0== Riv DO
7.0<Dv 7.0<− OI vv
7.00 <−Iv
V7.0<DvA0=Di{
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10Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks analysisC3 – DR switching circuits
Step 3. Find vO and the range for vIby replacing the diode’s equations in the circuit’s equations.
Example
D – (on)
Deduce and plot VTC vO (vI)
Rivvvv
DO
ODI
==++− 0
{ A0>Di
V7.0=Dv
07.0 =++− OI vv
Rvi O
D =
V7.0>Iv
7.0−= IO vv
0>Ov
07.0 >−Iv
0>RvO
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11Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks analysisC3 – DR switching circuits
Step 4. Write down the complete expression of VTC vO (vI) and plot it, for D-(on) and D-(off).
Example
Deduce and plot VTC vO (vI)
slope = 1
Application:
Voltage rectifier=OvV7.0<Iv
V,7.0−Iv V7.0>Iv
,0
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12Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks analysisC3 – DR switching circuits
Example
slope = 1
Waveforms
=OvV7.0<Iv
V,7.0−Iv V7.0>Iv
,0
-2
0
2
inpu
t vol
tage
[V]
t
-2
0
2ou
tput
vol
tage
[V]
t
1.3V
0.7V
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13Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks analysisC3 – DR switching circuits
Influence of VTh and VD,on
Waveforms
-50
0
50
t
-0.5
0
0.5
t
vI [V]
vO [V]
-2
-1
0
1
2
t
-10
-5
0
5
10
t
If the input voltage is large enough (>> 0.7 V) VTh can be considered 0 V VD,on can be neglected, meaning that for D – (on), vO = vI
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14Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks analysisC3 – DR switching circuits
Example iD
vD
a) How does the output voltage look like if the input is a sine wave, 3 V amplitude and 2 V offset?b) What is the peak forward current through diode for R = 2 kΩ?
c) What is the peak reverse voltage vDR across D (vDR=- vD)?d) Repeat a) and b) if the offset of the input voltage becomes -4 V.e) Repeat the above points, assuming the diode is reversed in the circuit.
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15Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks analysisC3 – DR switching circuits
Other series connections
Reverse the diode
Change the places of D and R (output voltage collected from D)
Never connect a voltage source so that during normal operation, the source can be short-circuited.
!Forbidden connection!
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16Laura-Nicoleta IVANCIU, Electronic devices
Two-port DR networks analysisC3 – DR switching circuits
Loaded two-port networks
What are the effects of RL on the VTC and on the output voltage?
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17Laura-Nicoleta IVANCIU, Electronic devices
Applications of two-port DR networks
Half-wave rectifier
C3 – DR switching circuits
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18Laura-Nicoleta IVANCIU, Electronic devices
Applications of two-port DR networks
Pulses selector
C3 – DR switching circuits
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19Laura-Nicoleta IVANCIU, Electronic devices
Applications of two-port DR networks
Voltage limiters (clamp networks)
simple
double
Reverse engineering: Use the waveforms to deduce and plot VTC vO (vI).
C3 – DR switching circuits
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20Laura-Nicoleta IVANCIU, Electronic devices
Applications of two-port DR networks
Maximum multi-port networks
>>
V7.0A
BA
vvv
V7.0);(),( 21 −=−− BO vvonDoffD
0);(),( 21 =−− OvoffDoffD
)V0;V7.0;V7.0max( −−= BAO vvv
V7.0);(),( 21 −=−− AO vvoffDonD
>>
V7.0B
AB
vvv
<<
V7.0V7.0
B
A
vv
C3 – DR switching circuits
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21Laura-Nicoleta IVANCIU, Electronic devices
Applications of two-port DR networks
Maximum multi-port networks
vO= max(vA – 0.7 V; vB – 0.7 V; 0)
vO= max(vA; vB; 0) neglecting 0.7 V
What is the peak value of the current through each circuit element if R=5 kΩ?
What is the range of values for R, if the peak forward current through each diode is 200 mA?
C3 – DR switching circuits
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22Laura-Nicoleta IVANCIU, Electronic devices
Applications of two-port DR networks
Minimum multi-port networks
vO= min(vA+ 0.7 V; vB+ 0.7 V; VPS)
vO= min(vA; vB; VPS) neglecting 0.7 V
Plot vO(t).
C3 – DR switching circuits
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23Laura-Nicoleta IVANCIU, Electronic devices
Applications of two-port DR networks
Back-up supply from a 9 V battery
)V3.11;V3.8max(=PSV
C3 – DR switching circuits
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24Laura-Nicoleta IVANCIU, Electronic devices
SummaryAlthough the war is not over, today we won the battle against:
Two-port DR networks. DR switching circuits. Voltage transfer characteristic (VTC) Two-port DR networks analysis Applications of two-port DR networks
Next week: Full-wave DR rectifiers. DC switching circuits. DRC rectifiers. LEDs.
To do: Homework 1
C3 – DR switching circuits