CONTROLABLE SWITCHING DEVIES

DESIGNED

BY

DR. SAMEER KHADER

PPU

“E-learning Project”

CHAPTER SEVEN (New textbook)

Diac Circuits

Triac Circuits

Thryristor Circuits

CONTENT

Introduction, Classification &Applications,

Practical Firing ( Triggering) Circuits

Thyristor Commutation (turning-off)

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

P N P NA K

GA

G

KPrinciple of operation :The thyristor constructionPresents 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 :

A K

GD3D2D1

Th.

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)

Gate-firing method: the firing circuit is shown below: Thyristor

I-V curve

Thyristor Main Parameters:

There’re 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 0.8…12V;

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/decreasing) of thyristor voltage .

Thyristor Dynamic Performances DC

50 Hz

V2220/-220V

SCR22N5064

R310k 30%D4BAR74

R4100

DC

35.00ms 50.00ms 65.00ms 80.00ms

250.0 V

150.0 V

50.00 V

-50.00 V

-150.0 V

-250.0 V

A: v2_1

35.00ms 50.00ms 65.00ms 80.00ms

1.250 V

0.750 V

0.250 V

-0.250 V

-0.750 V

A: d4_k

35.00ms 50.00ms 65.00ms 80.00ms

2.250 A

1.750 A

1.250 A

0.750 A

0.250 A

-0.250 A

A: r4[i]

35.00ms 50.00ms 65.00ms 80.00ms

250.0 V

150.0 V

50.00 V

-50.00 V

-150.0 V

-250.0 V

A: scr2_1

S3

50 Hz

V585/-85V SCR6

BRX44

+

C31.0uF

R85k 90%

SCR5MCR22-4

R102.5k

R950

0

SCR5_3

SCR5_2

R8_1

SCR5_1

V5_1

0.000ms 15.00ms 30.00ms 45.00ms

100.0 V

50.00 V

0.000 V

-50.00 V

-100.0 V

A: s4_1

0.000ms 15.00ms 30.00ms 45.00ms

90.00 V

70.00 V

50.00 V

30.00 V

10.00 V

-10.00 V

A: scr5_1

0.000ms 15.00ms 30.00ms 45.00ms

150.0 W

100.0 W

50.00 W

0.000 W

A: r10[p]

V-source V-source

V-gate V-gate

V-thyris

P-loadP-load

AS2

+ V480V

SCR3BRX45

S1

R55k 60%

+

C21.0uF

SCR4MCR22-3

50 Hz

V3120/-120V

R60.5k

R750

A

S1_2

0

V3_1

V4_1

SCR4_1

R5_3

SCR4_2

C2_1

0.000ms 15.00ms 30.00ms 45.00ms

125.0 V

75.00 V

25.00 V

-25.00 V

-75.00 V

-125.0 V

A: r5_3

0.000ms 15.00ms 30.00ms 45.00ms

2.000 V

0.000 V

-2.000 V

-4.000 V

-6.000 V

A: scr3_1

0.000ms 15.00ms 30.00ms 45.00ms

25.00 V

-25.00 V

-75.00 V

-125.0 V

A: scr4_1

0.000ms 15.00ms 30.00ms 45.00ms

300.0 W

200.0 W

100.0 W

0.000 W

A: r7[p]

V-source

V-gate

V-thyris

P-load

AS2

+ V480V

SCR3BRX45

S1

R55k 60%

+

C21.0uF

SCR4MCR22-3

50 Hz

V3120/-120V

R60.5k

R750

A

R5_3

0

R5_3

V4_1

SCR4_1

R5_3

SCR3_1

SCR3_1

0.000ms 0.300ms 0.600ms 0.900ms

87.00 V

85.00 V

83.00 V

A: s1_1

0.000ms 0.300ms 0.600ms 0.900ms

1.3940 V

1.3938 V

1.3936 V

A: scr3_1

0.000ms 0.300ms 0.600ms 0.900ms

1.65525 V

1.65475 V

1.65425 V

1.65375 V

1.65325 V

1.65275 V

A: scr4_1

0.000ms 0.300ms 0.600ms 0.900ms

138.936 W

138.934 W

138.932 W

138.930 W

138.928 W

A: r7[p]

V-source

V-gate

V-thyris

P-load

AC -circuit

DC -circuit

2-Phase Control Gate Firing Circuits: 1- RC relaxation oscillator

Th2Th1 Th1

Th2

C C

R-load

R1 R1

R2 R2

R-load

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: R2<<R1; and R-load << R1; * DC source VBOTh2 < Vs ; and IH2 < Vs/R1; ** AC source VBOTh2 < Vm; and IH2 < Vm/R1; Vs(t)=Vm.sin (t);

Vc t( ) Vs 1 e

t

Vs

R1 CR1

Vc tp( ) VBOTh2VBOTh2

tp R1 C lnVs

Vs VBOTh2R1

Vs

Vs VBOTh2

The thyristor Th2 will

conduct when Vc=VBOTh2; This could be

occurred at t=tp ; this time

called (firing instant)

min sin 1 VTG

Vm

VTG

Vm

max sin 1 Vm

Vm

Vm

Vm

R1minVm

IGTRGK

Vm

IGTRGK

RGKVGT

IGT

VGT

IGT

R1maxVm

IGmaxRGK

Vm

IGmaxRGK

tp360

Ttp

The firing angle of previous firning circuits in AC circuit canDetermine as follow :

9<<90 ( without C)

I-V curve

•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 > + 0.85 V at least; VBR > Vm ; ILmin > IL at firing( remains conduct); and ILmin < 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 .

Conclusion

Chapter 7-B

Triac Circuits1- 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- Circuit application:

3- I-V Curve:

Triac Firing Circuits

2.500 V

Triacvoltage

Loadcurrent

Gatevoltage

Load

35.00ms 50.00ms 65.00ms 80.00ms

200.0 V

100.0 V

0.000 V

-100.0 V

-200.0 V

A: r2_2

Triacvoltage

35.00ms 50.00ms 65.00ms 80.00ms

2.500 A

1.500 A

0.500 A

-0.500 A

-1.500 A

-2.500 A

A: r2[i]

Loadcurrent

35.00ms 50.00ms 65.00ms 80.00ms

1.500 V

0.500 V

-0.500 V

-1.500 V

A: d1_k

Gatevoltage

D1100HF120PV

+

C11uF

MAC210-6

R110k 5%

50 Hz

V1220/-220V

BA

R2100

BA

0.000ms 15.00ms 30.00ms 45.00ms

300.0 V 200.0 V 100.0 V 0.000 V-100.0 V-200.0 V-300.0 V

0.000ms 15.00ms 30.00ms 45.00ms

3.000 A 2.000 A 1.000 A 0.000 A-1.000 A-2.000 A-3.000 A

0.000ms 15.00ms 30.00ms 45.00ms

1.500 V 1.000 V 0.500 V 0.000 V-0.500 V-1.000 V-1.500 V

D1100HF120PV

+ C10.3uF

MAC210-6

R110k 20%

50 Hz

V1220/-220V

BA

R2100

BA

1- Phase angle control without diode 2- Phase angle control with diode

Pulse generator

AC source

S1

0.5uF

UJT

2N2646

20V

D

Tr

Q2004L4

C

B

100 Hz

0/15V

A

50 Hz

120/-120V

R59k

R4150

R347

R120

Rload100

D

C

B

A

0.000ms 10.00ms 20.00ms 30.00ms

25.00 V

15.00 V

5.000 V

-5.000 V

-15.00 V

-25.00 V

A: tr_3

0.000ms 10.00ms 20.00ms 30.00ms

125.0 V

75.00 V

25.00 V

-25.00 V

-75.00 V

-125.0 V

A: v3_1

0.000ms 10.00ms 20.00ms 30.00ms

125.0 V

75.00 V

25.00 V

-25.00 V

-75.00 V

-125.0 V

A: tr_2

0.000ms 10.00ms 20.00ms 30.00ms

5.000 V

3.000 V

1.000 V

-1.000 V

-3.000 V

-5.000 V

A: tr_3

0.000ms 10.00ms 20.00ms 30.00ms

250.0 V

150.0 V

50.00 V

-50.00 V

-150.0 V

-250.0 V

A: tr_2

5.000ms 15.00ms 25.00ms 35.00ms

25.00 V

15.00 V

5.000 V

-5.000 V

-15.00 V

-25.00 V

A: c1_2

UJTneedles

Loadvoltag

e

Pulsegenerator

Loadvoltag

e

Capacitorvoltage

Source voltage

3-Triac firing circuits using UJT

B1

B2

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 :

Vdc2

T0

T

2

tVm sin t( ) d

Vrms2

T 0

T

2

tVmsin t( )2d

2

T

Prms ( ) Pmax cosPmax

PmaxVrms 0( )

2

RLoad

Vrms

Pdc ( ) Pdcmax cosPdcmax

PdcmaxVdc 0( )

2

RLoad

Vdc 0( )

1- when 0<</2 0<Vrms<Vs; 2- Vdc=0 for symmetrical firing 3- Vdc0 for asymmetrical firing 4- the existing of inductance , reduced The control rang of Prms=F().

UJT – circuit:

tp R1 C lnVBB

VBB Vp tp( )R1

VBB

VBB Vp *

,VBB-base to base UJT’s voltage:, ujt- UJT’s intrinsic factor <=1,Vp- UJT’s peak voltage;, tp-delay time ( firing instant) .

XrRBB

RBB R4

RBB

RBB R4Vp tp( ) ujt Xr VBB 0.6

Vp t tp( ) Vc tp( )t tp

Vc tp( ) VBB 1 e

tp

Chapter 7C

Diac Circuits1- 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:

3- Circuit modification:

4- I-V Curve:

5- Time-varying performances:

Phase control circuit with Diac & Triac:

Vd Vc x( )x

Vc C( ) Vcm sinxVc C( )Vc

Vcm 2Vs

1 RC2

Vs

RC

c tan 1 RC( )RC

c xc x

The main equations are as follow , and can derives when Vdiac =Vc at given angle.

The firing angle

Additional Firing circuits

C10.5uF

Q12N2646D2

BZG03C30

R46k 10%

SCR210RIA20

S1

50 Hz

V260/-60V

D118DB2

R850

R7250

R650

R550

0.000ms 15.00ms 30.00ms 45.00ms

65.00 V

45.00 V

25.00 V

5.000 V

-15.00 V

-35.00 V

A: d1_3

0.000ms 15.00ms 30.00ms 45.00ms

65.00 V

45.00 V

25.00 V

5.000 V

-15.00 V

-35.00 V

A: r4_3

0.000ms 15.00ms 30.00ms 45.00ms

40.00 V

30.00 V

20.00 V

10.00 V

0.000 V

-10.00 V

A: r4_1

0.000ms 15.00ms 30.00ms 45.00ms

3.500 V

2.500 V

1.500 V

0.500 V

-0.500 V

-1.500 V

A: scr2_2

0.000ms 15.00ms 30.00ms 45.00ms

61.00 V

41.00 V

21.00 V

1.000 V

-19.00 V

-39.00 V

A: scr2_1

0.000ms 15.00ms 30.00ms 45.00ms

71.00 W

51.00 W

31.00 W

11.00 W

-9.000 W

-29.00 W

A: r5[p]

0.000ms 15.00ms 30.00ms 45.00ms

1.250 V

0.750 V

0.250 V

-0.250 V

-0.750 V

-1.250 V

A: scr2_2

0.000ms 15.00ms 30.00ms 45.00ms

60.00 V

40.00 V

20.00 V

0.000 V

-20.00 V

-40.00 V

A: scr2_1

0.000ms 15.00ms 30.00ms 45.00ms

60.00 W

40.00 W

20.00 W

0.000 W

-20.00 W

-40.00 W

A: r5[p]

Source voltage

Zenervoltage

Capacitor voltage

Gate needles

Thyristorvoltage

Loadpower

Gate needles

Thyristorvoltage

Loadpower

1- Practical circuit using UJT:

1- Low =R4C12- High =R4C1

T11TO1

D418DB2

50 Hz

V160/-60V

S2

SCR110RIA20

R16k 30%

D3BZG03C30

Q22N2646C2

1.5uF

R1050

R950

R3250

R2150

0.000ms 15.00ms 30.00ms 45.00ms

66.50 V

16.50 V

-33.50 V

A: c2_2

0.000ms

15.00ms

30.00ms 45.00ms

26.50 V

6.500 V

-13.50 V

A: q2_2

0.000ms 15.00ms 30.00ms 45.00ms

2.000 V

1.000 V

0.000 V

A: scr1_2

0.000ms 15.00ms 30.00ms 45.00ms

50.00 V

0.000 V

-50.00 V

A: scr1_1

5.000ms 20.00ms 35.00ms 50.00ms

100.0 W

0.000 W

-100.0 W

A: r10[p]

Gate needles

Capacitor voltage

Thyristorvoltage

Loadpower

UJT Signal at

B2B1

B2

2- Practical circuits using UJT and Isolation Transformer:

5.000ms 20.00ms 35.00ms 50.00ms

7.500 V

2.500 V

-2.500 V

A: c2_2

5.000ms 20.00ms 35.00ms 50.00ms

1.000 V

0.500 V

0.000 V

A: scr1_2

5.000ms 20.00ms 35.00ms 50.00ms

50.50 V

0.500 V

-49.50 V

A: scr1_1

5.000ms 20.00ms 35.00ms 50.00ms

100.5 W

0.500 W

-99.50 W

A: r10[p]

Capacitor voltage

Gate needles

Thyristorvoltage

Loadpower

D11N5402

C42uF

C12uF

Q2MAC15A6

D31N5402

SCR2S2003LS1

SCR1

S2003LS1

S1

50 Hz

V3120/-120V

R10.1k

R80.9k

R747

R60.1k

R50.9k

R40.1k

0.000ms 30.00ms 60.00ms 90.00ms

250.1 V

150.1 V

50.10 V

-49.90 V

-149.9 V

-249.9 V

A: r6_2

0.000ms 30.00ms 60.00ms 90.00ms

250.1 V

150.1 V

50.10 V

-49.90 V

-149.9 V

-249.9 V

A: r8_2

0.000ms 30.00ms 60.00ms 90.00ms

250.1 V

150.1 V

50.10 V

-49.90 V

-149.9 V

-249.9 V

A: r5_1

0.000ms 15.00ms 30.00ms 45.00ms

15.00 V

5.000 V

-5.000 V

-15.00 V

-25.00 V

-35.00 V

A: r6_1

0.000ms 15.00ms 30.00ms 45.00ms

1.250 A

0.750 A

0.250 A

-0.250 A

-0.750 A

-1.250 A

A: r6[i] 0.000ms 15.00ms 30.00ms 45.00ms

150.0 W

100.0 W

50.00 W

0.000 W

-50.00 W

-100.0 W

A: r6[p]

0.000ms 15.00ms 30.00ms 45.00ms

12.49 W

7.490 W

2.490 W

-2.510 W

-7.510 W

-12.51 W

A: c1[p]

3: ON-OFF firing circuit :This circuit illustrates firing techniques used in AC Voltage controller based on so called ON-OFF method, where it’s necessary to fire the thyristor at the beginning of both half-cycles .

Source voltag

e

Vg-th1

Vg-th2

V-triac

I-load

P-load

Ic1

Load

S1SCR2

S2003LS1

C22uF

D11N5402

SCR1S2003LS1

C12uF

50 Hz

V1120/-120V R5

4.1kR40.1k R3

0.9kR15.1k

S1SCR2

S2003LS1

C22uF

D11N5402

SCR1S2003LS1

C12uF

50 Hz

V1120/-120V R5

5.1kR40.1k R3

0.9kR15.1k

20.00ms 50.00ms 80.00ms 110.0ms

250.0 V

150.0 V

50.00 V

-50.00 V

-150.0 V

-250.0 V

A: v1_1

20.00ms 50.00ms 80.00ms 110.0ms

250.0 V

150.0 V

50.00 V

-50.00 V

-150.0 V

-250.0 V

A: scr1_2

20.00ms 50.00ms 80.00ms 110.0ms

250.0 W

150.0 W

50.00 W

-50.00 W

-150.0 W

-250.0 W

A: r4[p]

20.00ms 50.00ms 80.00ms 110.0ms

300.0 V

100.0 V

-100.0 V

-300.0 V

A: v1_2

Zero-Voltage switching

S=Off S=ONS S

20.00ms 50.00ms 80.00ms 110.0ms

200.0 V

0.000 V

-200.0 V

A: v1_1

20.00ms 50.00ms 80.00ms 110.0ms

10.00 V

0.000 V

-10.00 V

A: scr1_3

20.00ms 50.00ms 80.00ms 110.0ms

5.000 V

0.000 V

-5.000 V

A: scr1_2

20.00ms 50.00ms 80.00ms 110.0ms

200.0 W

0.000 W

-200.0 W

A: r4[p]

V-source

Vg-th1

Vth1

Load power

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 model4. To determine the turning-off time, and how could be affected5. 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.

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: ILoad<IH . 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:

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

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: ILoad<IH

- 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: 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.

C.Lt

);tcos1(Vs)t(VcC.L

1;

L

C.VsI

tsin.I)t(i

o

m

m

Mathematical modeling:

*- 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:T1=ON

;Vs)0(Vc

;2R1RR

2ln.C.Rt

:timeoffturningThe

C.R;.i

)t(Vc)t(i.RVs

off

/t

R

Vs.2)t(1

Let Vs=200V; R=5Ω; =10µFTherefore:

toff=34.4µS

Waveforms: Hereinafter the circuit waveforms for both T1, T2, Vg1, Vg2, I1,I2,

and VR1.

*- 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:T1=ON, after then T2=ON

;Vs)0(Vc

2ln.C.Rt

:timeoffturningThe

)21.(Vs)t(Vc

C.R;.i

)0(Vc)t(iC

1)t(i.R

)t(Vc)t(i.RVs

off

/t

/t

R

Vs.2)t(

t

0

Let Vs=200V; R=5Ω; =10µF

Therefore: toff=34.6µS

Waveforms: Hereinafter the circuit waveforms for both T1, T2, Vg1, Vg2, I1, and

Vload.

*- 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

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