ENG 201- Diode Applications
-
Upload
mohamed-khairy -
Category
Documents
-
view
226 -
download
0
Transcript of ENG 201- Diode Applications
-
7/24/2019 ENG 201- Diode Applications
1/44
1
Diode Applications(ENG-201)Dr. Hamdy Abd Elhamid
mailto:[email protected]:[email protected] -
7/24/2019 ENG 201- Diode Applications
2/44
Outline
1- Rectifiers:- Half-Wave,
- Full Wave,
- Bridge .
2- Signal Clipping
- Positive Clipping- Negative Clipping
3- Clamper
- Positive Clamper
- Negative Clamper
4- Voltage regulators
-
7/24/2019 ENG 201- Diode Applications
3/44
Block diagram of a rectifier and a dc power supply with a load.
-
7/24/2019 ENG 201- Diode Applications
4/44
Half-wave rectifier operation. The diode is considered to be ideal.
-
7/24/2019 ENG 201- Diode Applications
5/44
The effect of the barrier potential on the half-wave rectified outputvoltage is to reduce the peak value of the input by about 0.7 V.
Vp
0
-VP
2
Vi(t)
t
VD
Vp- VD
0 2
Vo(t)
t
-
7/24/2019 ENG 201- Diode Applications
6/44
Average value of the half-wave rectified signal.
V
cos2V
d0dsinV2
1
dtVT
1V
P
0
P
2
0 p
T
0DC
-
7/24/2019 ENG 201- Diode Applications
7/44
Root Mean Square (RMS) Value
4
V
sin4
V
d2cos12
1
2
Vd
2
V
d0dsinV21
dtVT
1V
P
0
P
P
0
P
2
0
2p
T
0
2
rms
2
2
0
2
2
2
2
2
22
1
sin
VDC
Vrms
t0
t1
t2
t3
Vp
VO
t
-
7/24/2019 ENG 201- Diode Applications
8/44
The PIVoccurs at the peak of each half-cycle of the input voltage when the diode isreverse-biased. In this circuit, the PIV occurs at the peak of each negative half-cycle.
-
7/24/2019 ENG 201- Diode Applications
9/44
Half-wave rectifier with transformer-coupled input voltage.
-
7/24/2019 ENG 201- Diode Applications
10/44
Full-wave rectification.
A center-tapped full-wave rectifier. Full-Wave Bridge Rectifier
http://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppthttp://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppthttp://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppthttp://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppt -
7/24/2019 ENG 201- Diode Applications
11/44
Basic operation of a center-tapped full-wave rectifier. Note that the current through theload resistor is in the same direction during theentire input cycle, so the output voltagealways has the same polarity.
A center-tapped full-wave rectifier.
-
7/24/2019 ENG 201- Diode Applications
12/44
Average Value
V2
cos
V
dsinV
1
dtVT
1V
P
0
P
0 p
T
0DC
2
V
sin2
V
d2cos12
1
V
dsinV
1
dtVT
1V
P
0
P
P
0
2
p
T
0
2
rms
2
2
0
2
2
2
22
1
RMS Value
-
7/24/2019 ENG 201- Diode Applications
13/44
Center-tapped full-wave rectifier with a transformer turns ratio of 1. Vp(pri) is the peak value of the primaryvoltage.
Center-tapped full-wave rectifier with a transformer turns ratio of 2.
-
7/24/2019 ENG 201- Diode Applications
14/44
Full-Wave Bridge Rectifier
http://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppthttp://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppthttp://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppthttp://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppt -
7/24/2019 ENG 201- Diode Applications
15/44
15
Full-Wave Bridge Rectifier
http://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppthttp://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppthttp://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppthttp://c/Documents%20and%20Settings/Dr%20Hamdy/Local%20Settings/Temp/Lecture%205%20Bridge%20rectifier.ppt -
7/24/2019 ENG 201- Diode Applications
16/44
16
Bridge operation during a positive half-cycle of the primary and secondary voltages.
-
7/24/2019 ENG 201- Diode Applications
17/44
Vp
0
-VP
2
Vi(t)
t
Vp- VD
0 2
Vo(t)
t
17
DC Value =???
-
7/24/2019 ENG 201- Diode Applications
18/44
18
Peak inverse voltages across diodes D3and D4in a bridge rectifier duringthe positive half-cycle of the secondary voltage.
-
7/24/2019 ENG 201- Diode Applications
19/44
19
Power supply filtering.
Download datasheet
-
7/24/2019 ENG 201- Diode Applications
20/44
20
Operation of a half-wave rectifier with a capacitor-input filter. The currentindicates charging or discharging of the capacitor.
Vr(pp)=
-
7/24/2019 ENG 201- Diode Applications
21/44
21
Half-wave ripple voltage (green line).
Vr(pp)=
-
7/24/2019 ENG 201- Diode Applications
22/44
22
Vr and VDCdetermine the ripple factor.
Vp(rect) : unfiltered peak rectified voltage
Vr(pp) : peak to peak ripple voltage
VDC : average value of ripple voltage
rhwrVr(pp)
VDC
1
2 3fRLC
rfwrVr(pp )
VDC
1
4 3fRLC
-
7/24/2019 ENG 201- Diode Applications
23/44
23
Effects of RLand C
C=1000F C=470F
C=100F
R=1500
R=1000
R=500
(a) RLfixed (b) Cfixed
-
7/24/2019 ENG 201- Diode Applications
24/44
Type of
Rectifier
PIV
Half Wave Peak value of the input secondary voltage, Vs(peak)
Full Wave :
Center-Tapped
2Vsecondary(peak)- V
Full Wave:Bridge
Vsecondary(peak)- V
-
7/24/2019 ENG 201- Diode Applications
25/44
25
Diode Limiters (Clipper)
Clippers are networks that employ diodes to clip
away a of an input signalwithout distorting the
remaining part of the applied waveform.
-
7/24/2019 ENG 201- Diode Applications
26/44
26
Diode Limiters (Clipper)
in
L
L
out
VRR
R
V
1
-
7/24/2019 ENG 201- Diode Applications
27/44
27
Example
What would you expect to see displayed on an oscilloscope connected across RL in thelimiter shown in above figure.
VVk
kV
RR
RV in
L
L
out 09.9101.1
0.1
1
Assume approximate diode is used, Vd = 0.7 V
-
7/24/2019 ENG 201- Diode Applications
28/44
28
Biased Limiters (Clippers)
A positive limiter
A negative limiter
-
7/24/2019 ENG 201- Diode Applications
29/44
29
Modified Biased Limiters (Clippers)
-
7/24/2019 ENG 201- Diode Applications
30/44
30
Summary
Limiters(Clippers)
In this examples
VD= 0
In analysis, VD
= 0
or VD= 0.7 V can
be used. Both are
right assumption.
-
7/24/2019 ENG 201- Diode Applications
31/44
31
Diode Clampers
Positive clamper operation.
Negative clamper operation
-
7/24/2019 ENG 201- Diode Applications
32/44
32
Diode Clamper (Square wave)
Diode Clamper
Diode ON stateDiode OF state Output
VVc= 0 ; Vc= V; Vo= 0.7 V but
ideal Vo= 0V
-V - Vc- Vo = 0; Vc = V
Vo= -2 V
-
7/24/2019 ENG 201- Diode Applications
33/44
33
Summary of Clamper Circuits
-
7/24/2019 ENG 201- Diode Applications
34/44
34
Voltage Multipliers
Voltage Doubler
Voltage Tripler
Voltage Quadrupler
Voltage multiplier circuits use a combination of diodes and capacitors
to step up the output voltage of rectifier circuits.
-
7/24/2019 ENG 201- Diode Applications
35/44
35
Voltage Doubler
35
Positive Half-Cycle
o D1conducts
o D2is switched off
o Capacitor C1charges to Vm
Negative Half-Cycleo D1is switched off
o D2conducts
o Capacitor C2charges to Vm
Vout = VC2= 2Vm
-
7/24/2019 ENG 201- Diode Applications
36/44
36
Zener Diodes
The zener diode
silicon pn-junction device-designed for operate inthe reverse-biased region
Schematic diagram shown that this particular zener
circuit will work to maintain 10 V across the load
Zener diode symbol
-
7/24/2019 ENG 201- Diode Applications
37/44
37
Zener Diodes
Breakdown voltageset by controlling the doping level during manufacture
When diode reached reverse breakdownvoltage remains constant- current changedrastically
If zener diode isFBoperates the same as a rectifier diode
A zener diodeis much like a normal diodebut if it is placed in the circuit in reverse
bias and operates in reverse breakdown.
Note that its forward characteristics are just like a normal diode.
1.8V200V
-
7/24/2019 ENG 201- Diode Applications
38/44
38
Zener Diodes
The reverse voltage (VR) is increasedthe reverse current (IR) remains extremely
small up to the kneeof the curve
Reverse currentcalled the zener current, IZ
At the bottom of the knee- the zener breakdown voltage (VZ) remains constant
although it increase slightly as the zener current, IZincrease.
IZKmin. current required to maintain voltage regulation
IZMmax. amount of current the diode can handle without being damage/destroyed
IZTthe current level at which the VZrating of diode is measured (specified on adata sheet)
The zener diode maintains a constant voltage for value of reverse current rating
from IZKto IZM
-
7/24/2019 ENG 201- Diode Applications
39/44
39
Zener Diodes(Zener Equivalent Circuit)
Since the actual voltage is not ideally vertical, the change in zener current
produces a small change in zener voltage
By ohms law:
Normaly -Zz is specified at IZT
Z
I
Z
V
Z
Z
Z
I
VZ
Zener impedance
-
7/24/2019 ENG 201- Diode Applications
40/44
40
Zener Diodes Applications
Zener diode can be used as
1. Voltage regulator for providing stable reference
voltages
2. Simple limiters or clippers
-
7/24/2019 ENG 201- Diode Applications
41/44
41
Zener Regulation with a Variable Load
The zener diode maintains a nearly constant voltage across RL
as long as the zener
current is greater than IZKand less than IZM
When the o/p terminal of the zener diode is open (RL=)-load current is zero and all of
the current is through the zener When a load resistor (R) is connected, current flow through zener & load RL, IL, IZ
The zener diode continues to regulate the voltage until IZ reaches its min value , IZK At this point, the load current is max. , the total current throughRremains
essentially constant.
-
7/24/2019 ENG 201- Diode Applications
42/44
10/26/201542
Example .Fig. (x) shows the zener regulator. Calculate (i) current through the series
resistance (ii) minimum and maximum load currents and (iii) minimum and maximum
zener currents. Comment on the results.
Solution.
-
7/24/2019 ENG 201- Diode Applications
43/44
10/26/201543
Example .A zener regulator has VZ = 15V. The input voltage may vary from 22 V to 40 V
and load current from 20 mA to 100 mA. To hold load voltage constant under all
conditions, what should be the value of series resistance ?
Solution. In order that zener regulator may hold output voltage constant under alloperating conditions, it must operate in the breakdown region. In other words,
there must be zener current for all input voltages and load currents. The worst
case occurs when the input voltage is minimum and load current is maximum
because then zener current drops to a minimum.
-
7/24/2019 ENG 201- Diode Applications
44/44
Zener Limiting
Zener diode also can be used in ac applications to limit voltage swings to desired level
a) To limit the +ve peak of a signal voltage to the selected zener voltage- Duringve alternation, zener arts asFBdiode & limits theve voltage to -0.7V
b) Zener diode is turn around
-Theve peak is by zener action & +ve voltage is limited to +0.7V
c) Two back-to-back zeners limit both peaks to the zener voltage7V
-During the +ve alternation, D2 is functioning as the zener limiterD1 is functioning
as aFBdiode.-During theve alternation-the roles are reversed