Switching characteristics during turn off, Electrical Engineering

Switching Characteristics During Turn off

The techniques  used for turning off a thyristor is known  as  commutation techniques. A  thyristor can be can be  turn off by reducing the forward  current to a level  below  the holding current IH.

The turn off  time ( toff ) is time in which  thyristor  regain its forward blocking  capability  means thyristor changed  its state form  on state off state.

The turn off time  t off  is the  sum of  reverse recovery time Irr and recombination time trc. In   t off time  all the excess carriers must be  removed  from  the four  layers  of SCR. After  the forward current  goes through the zero value, a reverse voltage  appears across the thyrisotr as shown  in figure1.12 this  reverse voltage accelerants the turn off  process by sweeping out the  excess  carriers  from outer junctions  J1 and J3,this is known  as reverse recovery period  and the  time  is reverse recovery time trr.

This  reverse  recovery  time is shown  in figure  between  time interval  t1  and t3.  The carriers around junction J2 and can be removed only by  recombination because this junction is present  between inner two layers. Actually after  reverse recovery period junction J2 has trapped charges and  these trapped charged  cannot flow  to the external circuit. Reverse voltage  should  be maintained across SCR for processing of recombination. Hence at the end  of turn off a depletion layer  develops  across  inner  junction J2 and the thyristor  recovers its ability to  withstand forward  voltages.

 

 

2126_Switching.PNG

                                                                    Figure Swithcing characteristics of SCR

Posted Date: 4/2/2013 3:51:33 AM | Location : United States







Related Discussions:- Switching characteristics during turn off, Assignment Help, Ask Question on Switching characteristics during turn off, Get Answer, Expert's Help, Switching characteristics during turn off Discussions

Write discussion on Switching characteristics during turn off
Your posts are moderated
Related Questions
Uninterruptable power  Supply An uninterruptible  power supply  provides emergency power when  utility power  is not  available. It  maintains the supply  under  all condition

Q. Sections construct in FORTAN? The sections construct is a no iterative work sharing construct which causes structured blocks to be shared among threads in team. Every struct

Q. Discuss in brief on combination clippers ? Combination clippers are a combination of biased positive and negative clippers. With a combination clipper, a portion of both pos

Explain iron and silicon iron alloys. Iron: Galvanised steel and iron wires that are usually used for earth conductor in low voltage distribution systems may also be utilize

what is the future scope of matlab in india?

can you help with my electronic principle assignment

Q. What do you mean by Negative Impedance Converter? The op-amp circuit of Figure causes a negative resistance R in between the input terminal and ground. In the more general

Determine the study of Robotics Robots can comprise embedded processors or be linked to a computer system. They are pre-programmed to do a specific task or taught' to remember

Q. Explain, with the aid of diagrams, the following in relation to the construction of power transformers. Include the advantages and disadvantages in your description. a) Core

Q. Calculate the stator input current? The parameters of the equivalent circuit shown in Figure for a three-phase, wye-connected, 220-V, 10-hp, 60-Hz, six-pole induction motor