Wednesday, 14 February 2018

Firing Circuits


Gate triggering is the most commonly used turn-on method employed to switch on the thyristors. Triggering circuits is also called firing circuits. There are various firing circuits available. R-Firing circuits is simple but suffer from limited firing circuits. Firing angle is limited between 0o to 90o. In actual practice firing angle can be varied between 3o to 90o. Limitation of the firing angle range of R-Firing circuit is eliminated by introducing a capacitor and a diode. Thus R-C firing circuits can increase the firing angle limitation range. Theoretically firing angle can be varied from 0o to 180o. However due to low voltage at 0o and 180o thyristor cannot be turn-on. Hence practically the range of firing angle is between 3o and 177o
Both R and R-C firing circuits suffer from following disadvantage:
  • They can be employed in power circuits having only one thyristor
  • They are capable of open loop control only
  • Due to lower voltages near 0o to 180o, gate current is small. Especially in R-C firing circuit, near 180o gate current is minimum due to maximum value of R. This will increase the turn on time, especially for R-L load, leading to higher turn on loss
  • Higher frequency gate signal is desirable for reliable turn on. Both the circuits are not capable of providing the same
  • There is no electrical isolation between control circuit and power circuit
However the circuits are simple and cheap. R-C firing circuits is widely used in low power thyristor controllers, such as solid state ac regulators for speed control of fans and blowers. R-C firing circuits can also acts as snubber circuit.


R-triggering and RC-triggering circuit notes : Click here to download
 

Friday, 9 February 2018

Turning off SCR [Commutation]

Commutation

  • To turn ON a SCR, a low voltage, short duration pulse is applied to the gate (typically 4V, 100µs).
  • Once the SCR is turned-on, the gate loses control and the SCR will only turn off when the load current falls virtually to zero, or the SCR is reverse biased.
  • The SCR will turn off naturally with a.c. supplies as the voltage reverses (which is called as Natural Commutation), but no such reversal occurs with d.c. supplies and it is necessary to force a voltage reversal if turn-off is to occur. This process is called Forced Commutation.
  • The process of turning OFF SCR is defined as "Commutation".
  • In all commutation techniques, a reverse voltage is applied across the SCR during the turn OFF process.
  • By turning OFF a SCR we bring it from forward conducting to the forward blocking mode.
      The conditions to be satisfied in order to turn OFF an SCR are:
  • IA < IH ( Anode current must be less than holding current).
  • A reverse voltage is applied to SCR for sufficient time enabling it to recover its  blocking state.
      There are two methods by which a SCR can be turned OFF.
                I. Natural Commutation
               II. Forced Commutation

Natural Commutation:

  • In AC circuit, the current always passes through zero for every half cycle.
  • As the current passes through natural zero, a reverse Voltage will simultaneously appear across the device. This will turn OFF the device immediately.
  • This process is called as natural commutation, since no external circuit is required for this purpose. It is also known as line commutation.
  • AC voltage controllers or phase voltage controllers are the example for the natural commutation.

Forced Commutation:

  • To turn OFF a SCR, the forward anode current should be brought to zero for sufficient time to allow the removal of charged carriers.
  • In case of DC circuits, the forward current should be forced to zero by means of some external circuits. This process is called as forced commutation.
  1. Class A or Self commutation
  2. Class B or Resonant commutation
  3. Class C or Complementary commutation
  4. Class D or Impulse or auxillary commutation
  5. Class E or External pulse commutation

Monday, 22 January 2018

Power Devices Assignment I (Create Video) for SY B



G.S.Mandal's
Maharashtra Institute of Technology,Aurangabad
Department of Electronics and Telecommunication Engineering
Assignment I
CLASS:SY B                                                                                        Part II 2017-18




Group No.
Roll No.
Name of the Student
Topic
1
T2483
MALI ASHWINI CHHOTULAL
Resistor
T2484
MHASKE SUNIL BHAGWAN
Capacitor
2
T2486
NAINAV PRIYANKA PRAKASH
Inductor
T2487
DHUMAL PRATIKSHA DNYANOBA
Diode
3
T2488
KARPE PRATIBHA ASARAM
Schottky diode
T2489
PATIL VIRENDRASINH RAMESHWAR
Zener diode
4
T2491
JEWALIKAR PRANESH ARUN
Power diode
T2492
PURI SWATI KALIDAS
IR LED
5
T2493
RAKHE APURVA ANILRAO
LED
T2494
RAUT SAURABH LAXMAN
7 Segment LED
6
T2495
SAHANE DIKSHA SANJAY
Tunnel diode
T2496
SASANE PRAJAKTA DILIP
Varactor diode
7
T2497
JADHAV SATISH ARUN
LCD
T2498
SEJUL SWATI DILIP
Transformer
8
T2499
SHAIKH SOHEB ANWAR MOHD YOUSUF ALI
Relay
T24100
SHINDE TIRTHESH SANDHU
Battery
9
T24101
GHUGE SHRADHA RAMCHANDRA
Fuse
T24102
TIWARI VYANKATESH SATYANARAYAN
Switches
10
T24103
UDAWANT RUSHIKESH RAJENDRA
MCB
T24104
UMAP VIKAS MADHUKAR
Earthing
11
T24105
VAIDYA VISHNU NIVRUTTI
Insulator
T24106
NAGRE VRUSHALI RAJENDRA
Connectors
12
T24107
WAGHMARE AISHWARYA BHASKAR
Types of wires
T24108
WAMBLE ADINATH YASHWANT
PCB
13
T24109
ZINE PRAVIN VISHWAS
Potentiometer
T24110
TANDALE DURGA UTTAMRAO
Thermistor
14
T24111
IGHE ADITYA GOVINDRAO
LDR
T24112
KHANDARE RAVINA RAJU
BJT
15
T24113
KHURUD ANKITA VIKAS
MOSFET
T24114
SHAH PRATIK PANKAJ
FET
16
T24115
INGLE TRUPTI VIJAY
JFET
T24116
PATIL VAISHNAVI BHAGVAN
UJT
17
T24117
VETAL VAIBHAV PHULCHAND
Power BJT
T24118
DANDGE CHITRAKALA PANDURANG
Power MOSFET
18
T24119
WADKAR ANJALI SANJAY
IGBT
T24120
TORNE MANISHA VISHWANATH
SCR
19
T24121
DALE MAYURI GANESH
TRIAC
T24122
KSHIRSAGAR SWAPNIL MAHADEV
DIAC
20
T24123
ANSARI AMER SK. JAFAR
GTO
T24124
DALVI MAYURI JAYANDRA
IC 555
21
T24125
NIMBALKAR DIPALI KANCHANRAO
LM35
T24126
KHAMAT GANESH SAHEBRAO
IC741
22
T24127
PANKHADE BIPIN RAVINDRA
IC7805
T24128
DHARMADHIKARI SHITAL DEEPAKRAO
IC7905
23
T24129
SHAIKH SAIF ALI SAHEBAN
IC 7404
T24130
DAUD SHUBHAM ASHOK
IC 7408
24
T24131
DANDGE NAGESH BABURAO
IC7486
T24132
KOTURWAR VAIBHAVI SUHAS
IC7432
25
T24133
SOVITKAR SHANTIKUMAR RAGHUNATH
IC 7400
T24134
GADEKAR SHIVPRASAD PRABHU
DC motor
26
T24135
KUBER RUSHIKESH KAKAJI
Solenoid Valve
T24136
DALKE PRIYANKA KESHAV
Piezoelectric sensor
27
T24137
KAWARKHE GOPAL CHANDRAKAT
CFL
T24138
SHIRSE MAYUR VITTHAL
LED Lamp
28
T24139
MOHAMMAD ATHAR MOHAMMAD AZHAR
Piezo buzzer
T24140
SHIRALE TIRTHPAKSH AMBADAS
Speaker
29
T24141
CHAVAN SHIVAM BABASAHEB
Microphone
T24142
RAUT SHUBHAM BHAGWAN
Optocoupler