CONTROLABLE SWITCHING DEVIES

1
CHAPTER SEVEN (New textbook)
CONTROLABLE SWITCHING DEVIES DESIGNED BY DR.
SAMEER KHADER PPU E-learning Project
2
CONTENT
Introduction, Classification Applications,
Thryristor Circuits
Triac Circuits
Diac Circuits
Practical Firing ( Triggering) Circuits
Thyristor Commutation (turning-off)
3
Chapter 7-A Thyristor Circuits
1- Construction Four PNPN layers with special
doping in each layer, with purpose to obtain
different electron and holes in these layers.
Each one has different potential voltage
Th.
N
N
P
P
A
K

K
A
G
Principle of operation The thyristor
construction Presents three diodes In series (
two forward biased and the third reverse
biased). The thyristor will conduct only if D2
forward biased, therefore current will flow from
A to K. This case could be achieved by different
ways as follow
G
A
K
D3
D1
D2
G
(1F)
4
Methods for Switching- on the thyristor
The switching process of the thyristor is called
Firing, because after Switching process is
ceased, WHERE the firing signal may can removed
with purpose to reduce the gate loss .There're
several methodS Applied to realize this purpose
1-Gate-firing method by supplying the
gate terminal with positive voltage ( this is the
most applied method - major method). 2-by
suddenly increasing the Anode voltage 3-by
increasing the thyristor temperature over
predetermined limit. 4- Photo effect
method, which used in photo devices ( Photo
thyristor)
Thyristor I-V curve
Gate-firing method the firing circuit is shown
below

(Expl.)
(Performance)
(Conclusion)
(Parameters)
5
Thyristor Main Parameters Therere several
parameters related to static dynamic
performance of the thyristor, these parameters
are as follow 1-VAK- thyristor voltage at
steady state ?2 V 2-VBO- -break over voltage ,
voltage after which thyristor will turning on at
constant gate current 3-VBR-
break down voltage in reverse biasing
state 4-IH- thyristor holding current this a
minimized load current keeping the thyristor in
conducting state ( if the current goes
down the thyristor will switch-off) 5- IL-
thyristor latching current this a minimized
load current keeping the thyristor in
conducting state after removing the gate signal
6-VGT- minimum gate voltage required to firing
the thyristor at given loadind condition
, VGT ? 0.812V 7-IGT- minimum gate
current., IGmax- maximum gate current 8-di/dt-
speed of (increasing/decreasing) of thyristor
current 9-dv/dt - speed of (increasing/decreas
ing) of thyristor voltage .

6
Thyristor Dynamic Performances
V-source
V-source
V-gate
V-gate
P-load
P-load
V-thyris
(Math Modeling)
(Gate Circuits)
7
2-Phase Control Gate Firing Circuits
1- RC relaxation oscillator
R-load
AC -circuit
DC -circuit
R-load
R1
R1
Th1
Th1
Th2
Th2
C
C
R2
R2
V-source
V-source
V-gate
V-gate
V-thyris
V-thyris
P-load
P-load
(Math Modeling)
8
Mathematical . Modeling
1- Gate firing circuit using RC relaxation
oscillator 2- Gate firing circuits using RC
circuit and called Phase control These circuits
may can use to fire thyristor in AC or DC
circuit in both sources the connected elements
must be with the following relations with purpose
to realized successful operation R2ltltR1 and
R-load ltlt R1 DC source VBOTh2 lt Vs and
IH2 lt Vs/R1 AC source VBOTh2 lt Vm and
IH2 lt Vm/R1 Vs(?t)Vm.sin (?t)
The thyristor Th2 will conduct when VcVBOTh2
This could be occurred at ttp this time
called (firing instant)
The firing angle of previous firning circuits in
AC circuit can Determine as follow
9?lt?lt90 ? ( without C)
9
I-V curve
10
Conclusion

• In DC source, tp- presents delay time , so by
  increasing Ig the thyristor allow more current
  to follow therefore increasing the load power
• In AC source, tp- presents delay angle which
  corresponds to ?tp.360/T, so by increasing Ig,
  ? decreases, thus load power increases
  P(?)Pmax . Cos(?), where Pmax-maximum allowable
  power.
• ? may can change from 0 to 90? ( without C) or
  to 145 ? (with C)
• The thyristor gate voltage must be gt 0.85 V
  at least
• VBR gt Vm ILmin gt IL at firing( remains
  conduct) and ILmin lt IH ( swith off) .
• By increasing di/dt at given Ig the thyristor
  capable to carry additional current ILoad .
• By increasing Ig, VBO ( ac circuits), which
  means that the thyristor
• is fired at earliest time , therefore
  increasing the load voltage and power .
• The gate pulse must removed after successfully
  firing the thyristor , with aim to reduce the
  gate losses .

11
Chapter 7-B Triac Circuits
1- Triac ( Triode Alternating Current Switch )
presents two parallel connected thyristors with
common gate, which energized with positive and
negative voltage. The main purpose of the Triac
is to control the RMS load voltage, therefore
there're several applications such as
Lighting control ( dimmer circuits) -
Temperature control
Torque speed control of induction machines.
2- Symbol
3- I-V Curve
3- Circuit application
12
Triac Firing Circuits
1- Phase angle control without diode
2- Phase angle control with diode
Load
Triac voltage
Triac voltage
300.0 V
200.0 V
200.0 V
A r2_2
100.0 V
100.0 V
0.000 V
-100.0 V
0.000 V
-200.0 V
-100.0 V
Load current
Load current
-300.0 V
0.000ms
15.00ms
30.00ms
45.00ms
-200.0 V
3.000 A
35.00ms
50.00ms
65.00ms
80.00ms
2.000 A
1.000 A
2.500 A
A r2i
0.000 A
1.500 A
-1.000 A
0.500 A
-2.000 A
-0.500 A
-3.000 A
0.000ms
15.00ms
30.00ms
45.00ms
-1.500 A
-2.500 A
Gate voltage
Gate voltage
1.500 V
35.00ms
50.00ms
65.00ms
80.00ms
1.000 V
2.500 V
0.500 V
1.500 V
0.000 V
A d1_k
-0.500 V
0.500 V
-1.000 V
-1.500 V
0.000ms
15.00ms
30.00ms
45.00ms
-0.500 V
(Math Modelation)
-1.500 V
35.00ms
50.00ms
65.00ms
80.00ms
13
3-Triac firing circuits using UJT
Source voltage
125.0 V
A v3_1
75.00 V
25.00 V
-25.00 V
-75.00 V
-125.0 V
0.000ms
10.00ms
20.00ms
30.00ms
Pulse generator
25.00 V
A tr_3
15.00 V
5.000 V
-5.000 V
-15.00 V
-25.00 V
0.000ms
10.00ms
20.00ms
30.00ms
Load voltage
B1
125.0 V
A tr_2
75.00 V
25.00 V
B2
-25.00 V
-75.00 V
-125.0 V
Capacitor voltage
0.000ms
10.00ms
20.00ms
30.00ms
UJT needles
5.000 V
A tr_3
3.000 V
25.00 V
A c1_2
1.000 V
15.00 V
-1.000 V
5.000 V
-3.000 V
-5.000 V
-5.000 V
-15.00 V
0.000ms
10.00ms
20.00ms
30.00ms
-25.00 V
5.000ms
15.00ms
25.00ms
35.00ms
Load voltage
250.0 V
A tr_2
150.0 V
50.00 V
(Math Modeling)
-50.00 V
-150.0 V
-250.0 V
0.000ms
10.00ms
20.00ms
30.00ms
14
Mathematical Modeling of Triac Circuits
Three main circuits are introduced with purpose
to fire the Triac device( Phase control with or
without diode, with UJT and with Diac device).
The presence of diode in the gate circuit remove
one half cycle , therefore convert the Triac into
Thyristor . In both circuits there are several
relations characterized the application of such a
device . These relations are as follow
1- when 0lt?lt?/2 0ltVrmsltVs 2-
Vdc0 for symmetrical firing 3- Vdc?0 for
asymmetrical firing 4- the existing of
inductance , reduced The control rang of
PrmsF(?).
UJT circuit
,VBB-base to base UJTs voltage , ?ujt- UJTs
intrinsic factor lt1 ,Vp- UJTs peak voltage ,
tp-delay time ( firing instant) .
15
Chapter 7C Diac Circuits
1- Diac ( Diode Alternating Current Switch )
presents two anti-parallel connected diodes with
special construction , aiming to maintain
relatively high threshold voltage across its
terminals . The main purpose of the Diac is to
divide the source voltage between its terminals
and the load terminals , therefore there're
several applications such as Firing
device in Triac gate circuit - Over
voltage protective device
2- Symbol
4- I-V Curve
3- Circuit modification
16
5- Time-varying performances
Phase control circuit with Diac Triac
(Math Modeling)
(Add. circuits)
17
The firing angle
The main equations are as follow , and can
derives when Vdiac Vc at given angle.
18
Additional Firing circuits
19
1- Practical circuit using UJT
Source voltage
65.00 V
A d1_3
45.00 V
25.00 V
5.000 V
-15.00 V
-35.00 V
0.000ms
15.00ms
30.00ms
45.00ms
Zener voltage
65.00 V
A r4_3
45.00 V
25.00 V
5.000 V
-15.00 V
-35.00 V
0.000ms
15.00ms
30.00ms
45.00ms
Capacitor voltage
40.00 V
A r4_1
30.00 V
20.00 V
Gate needles
10.00 V
0.000 V
-10.00 V
1.250 V
0.000ms
15.00ms
30.00ms
45.00ms
A scr2_2
0.750 V
Gate needles
0.250 V
3.500 V
A scr2_2
-0.250 V
2.500 V
-0.750 V
1.500 V
0.500 V
-1.250 V
0.000ms
15.00ms
30.00ms
45.00ms
-0.500 V
Thyristor voltage
-1.500 V
0.000ms
15.00ms
30.00ms
45.00ms
Thyristor voltage
60.00 V
A scr2_1
40.00 V
61.00 V
A scr2_1
20.00 V
41.00 V
0.000 V
21.00 V
1.000 V
-20.00 V
-40.00 V
-19.00 V
0.000ms
15.00ms
30.00ms
45.00ms
-39.00 V
Load power
0.000ms
15.00ms
30.00ms
45.00ms
Load power
60.00 W
A r5p
71.00 W
40.00 W
A r5p
51.00 W
20.00 W
31.00 W
0.000 W
11.00 W
-20.00 W
-9.000 W
-40.00 W
1- Low ?R4C1
2- High ?R4C1
-29.00 W
0.000ms
15.00ms
30.00ms
45.00ms
0.000ms
15.00ms
30.00ms
45.00ms
20
2- Practical circuits using UJT and Isolation
Transformer
Capacitor voltage
66.50 V
A c2_2
16.50 V
-33.50 V
UJT Signal at B2
0.000ms
15.00ms
30.00ms
45.00ms
26.50 V
A q2_2
B1
6.500 V
B2
15.00ms
-13.50 V
0.000ms
30.00ms
45.00ms
Gate needles
2.000 V
A scr1_2
Capacitor voltage
7.500 V
A c2_2
1.000 V
2.500 V
-2.500 V
0.000 V
5.000ms
20.00ms
35.00ms
50.00ms
Gate needles
0.000ms
15.00ms
30.00ms
45.00ms
Thyristor voltage
1.000 V
A scr1_2
50.00 V
A scr1_1
0.500 V
0.000 V
Thyristor voltage
0.000 V
5.000ms
20.00ms
35.00ms
50.00ms
-50.00 V
50.50 V
A scr1_1
0.000ms
15.00ms
30.00ms
45.00ms
Load power
0.500 V
100.0 W
A r10p
Load power
-49.50 V
5.000ms
20.00ms
35.00ms
50.00ms
0.000 W
100.5 W
A r10p
0.500 W
-100.0 W
5.000ms
20.00ms
35.00ms
50.00ms
-99.50 W
5.000ms
20.00ms
35.00ms
50.00ms
21
3 ON-OFF firing circuit This circuit
illustrates firing techniques used in AC Voltage
controller based on so called ON-OFF method,
where its necessary to fire the thyristor at
the beginning of both half-cycles .
Source voltage
250.1 V
A r6_2
150.1 V
50.10 V
-49.90 V
-149.9 V
-249.9 V
0.000ms
30.00ms
60.00ms
90.00ms
250.1 V
Vg-th1
Load
A r8_2
150.1 V
50.10 V
-49.90 V
-149.9 V
-249.9 V
0.000ms
30.00ms
60.00ms
90.00ms
250.1 V
Vg-th2
A r5_1
150.1 V
50.10 V
-49.90 V
-149.9 V
-249.9 V
0.000ms
30.00ms
60.00ms
90.00ms
V-triac
P-load
15.00 V
A r6_1
5.000 V
150.0 W
A r6p
-5.000 V
100.0 W
-15.00 V
50.00 W
-25.00 V
0.000 W
-35.00 V
-50.00 W
0.000ms
15.00ms
30.00ms
45.00ms
-100.0 W
1.250 A
0.000ms
15.00ms
30.00ms
45.00ms
I-load
Ic1
A r6i
0.750 A
12.49 W
A c1p
0.250 A
7.490 W
-0.250 A
2.490 W
-2.510 W
-0.750 A
-7.510 W
-1.250 A
(Zero-circuit)
-12.51 W
0.000ms
15.00ms
30.00ms
45.00ms
0.000ms
15.00ms
30.00ms
45.00ms
22
Zero-Voltage switching
SOff
SON
S
S
V-source
Vg-th1
Vth1
Load power
23
Chapter 7D Thyristor Commutation
1. Objectives 1. to study the concept of
thyristor commutation 2. to illustrate some of
commutation techniques 3. to study how to
express the required mathematical model 4. To
determine the turning-off time, and how could be
affected 5. Describing some examples
2. The Concept of Commutation Process - This
is a process of removing the circuit current by
forcing it to flow in another loop with purpose
to be ceased eliminated. - Depending on the
source voltage, there are two types of
commutation strategies - Natural commutation
applied in AC circuits - Forced commutation
Applied in DC circuits.
24
2.1 Natural Commutation Because of the load
current varies sinusoidally, the thyristor
should be turned off when the load current falls
below the holding value ILoadltIH . Furthermore,
in the negative half cycle, the applied source
voltage being negative with respect to
anode-cathode terminals, causing reverse biasing
of the device. Principle electrical circuit is
shown below
25
2.1 Forced Commutation In this case, because
of no alternating character of the current DC
, therefore it must force decreases by applying
the following approaches - the
load current must reduced below the holding
value ILoadltIH - by applying
negative voltage across the thyristor, causing
forced removing of internal charge, therefore
the load current falls below the holding value
IH . Several techniques realized these
approaches

• Self Commutation
• Complementary Commutation
• Resonant Commutation
• Impulse Commutation
• Load-side commutation
• Line-side commutation

26
- Self Commutation The thyristor is self
turning-off due to resonant behavior of the
current flows in RLC circuit as well shown on the
figure below, where it is clearly shown that when
the current becomes negative the thyristor
turned-off.
Mathematical modeling
27
- Complementary Commutation In this
case, second thyristor which called " Auxiliary"
operates in complementary sequence ( turning-on
first thyristor caused turning-off second device)
. The figure shown below illustrates the
principle circuit, where it is clearly shown that
each thyritor operates for predetermine time with
complementary sequence. The connected capacitor
play the role of applying negative voltage across
T1 and T2.
Mathematical modeling T1ON
Let Vs200V R5O 10µF Therefore toff34.4µS
28
Waveforms Hereinafter the circuit waveforms
for both T1, T2, Vg1, Vg2, I1,I2, and VR1.

29
- Impulse Commutation In this case,
second thyristor T2 which called " Auxiliary"
used to connect the capacitor across T1 with
inverse voltage, therefore reducing the thyristor
current below IH. The figure shown below
illustrates the principle circuit, where the
circuit waveforms illustrates these behaviors.
Mathematical modeling T1ON, after then T2ON
Let Vs200V R5O 10µF Therefore toff34.6µS
30
Waveforms Hereinafter the circuit waveforms
for both T1, T2, Vg1, Vg2, I1, and Vload.

31
- Resonant Commutation In this case,
second thyristor T2 used to connect the
capacitor across T1 with inverse voltage,
therefore reducing the thyristor current below
IH, while third thyristor T3 is used to
recharging the capacitor with polarity
appropriate to turning-off T1. The figure shown
below illustrates the principle circuit, where
the circuit waveforms illustrates these
behaviors.
Waveforms Hereinafter the circuit waveforms
for two cases 1- C is recharged through
resistance R2 2- C is recharged throug
inductance L2
32
(No Transcript)
33
THANK YOU FOR YOUR LISTENING
IF YOU HAVE QUESTIONS, PLEASE DONT HESTATE
TO CONTACT ME BY EMAIL ON sameer_at_ppu.edu