How Scr Works Analysis Essay Example

How Scr Works Analysis Essay How an SCR works? -Principle of Operation SCR Working Principle The SCR is a four-layer, three-junction and a three-terminal device and is shown in fig. a. The end P-region is the anode, the end N-region is the cathode and the inner P-region is the gate. The anode to cathode is connected in series with the load circuit. Essentially the device is a switch. Ideally it remains off (voltage blocking state), or appears to have an infinite impedance until both the anode and gate terminals have suitable positive voltages with respect to the cathode terminal. The thyristor then switches on and current flows and continues to conduct without further gate signals. Ideally the thyristor has zero impedance in conduction state. For switching off or reverting to the blocking state, there must be no gate signal and the anode current must be reduced to zero. Current can flow only in one direction. In absence of external bias voltages, the majority carrier in each layer diffuses until there is a built-in voltage that retards further diffusion. Some majority carriers have enough energy to cross the barrier caused by the retarding electric field at each junction. These carriers then become minority carriers and can recombine with majority carriers. Minority carriers in each layer can be accelerated across each junction by the fixed field, but because of absence of external circuit in this case the sum of majority and minority carrier currents must be zero. A voltage bias, as shown in figure, and an external circuit to carry current allow internal currents which include the follow ¬ing terms: The current Ix is due to †¢Majority carriers (holes) crossing junction J1 †¢Minority carriers crossing junction J1 Holes injected at junction J2 diffusing through the N-region and crossing junc ¬tion J1 and †¢Minority carriers from junction J2 diffusing through the N-region and crossing junction J1. Similarly I2 is due to six terms and I3 is due to four terms. The two simple analogues to explain the basic action for the thyristor are those of the diode and the two transistor models. 1. 1. Diode Model. The thyristor is similar to three d iodes in series as there are three P-N junctions. Without gate bias, there is always at least ne reverse biased junction to prevent conduction irrespective of the polarity of an applied voltage between anode and cathode. If the anode is made positive and the gate is also biased positively with respect to cathode, the P-layer at the gate is flooded by the electrons from the cathode and loses its identity as a P-layer. Accordingly the thyristor becomes equivalent to a conducting diode. Scr working 1. 2. Two Transistor Model. Imagine the SCR cut along the dotted line, as shown in fig. a. Then we can have two devices, as shown in fig. b. We will write a custom essay sample on How Scr Works Analysis specifically for you for only $16.38 $13.9/page Order now We will write a custom essay sample on How Scr Works Analysis specifically for you FOR ONLY $16.38 $13.9/page Hire Writer We will write a custom essay sample on How Scr Works Analysis specifically for you FOR ONLY $16.38 $13.9/page Hire Writer These two devices can be recognized as two transistors. The upper left one is P-N-P transistor and the lower right N-P-N type. Further it can be recognized that the base of the P-N-P transistor is joined to the collector of the N-P-N transistor while the collector of P-N-P is joined to the base of N-P-N transistor, as illustrated in fig. c. The gate terminal is brought out from the base of the N-P-N material. This construction has been conceived merely to explain the working of SCR, otherwise in physical shape the SCR has four solid layers of P-N-P-N type only. Now we can see that the two transistors are connected in such a manner that the collector of Q1 is connected to the base of Q2 i. e. the output collector current of Qt becomes the base current for Q2. In the similar way the collector of Q2 is joined to the base of Q1 which shows that the output collector current of Q2 is fed to Q1 as input base current. These are back to back connections of transistors in such a way that the output of one goes into as input of other transistor and vice-versa. This gives net gain of loop circuit as ? 1 x ? 2 where ? 1 and ? are current gains of two transistors respectively. When the gate current is zero or the gate terminal is open, the only current in circulation is the leakage current, which is very small in case of silicon device specially and the total current is a little higher than sum of individual leakage currents. Under these conditions P-N-P-N device is said to be in its forward blocking or high impedance ‘off state. As soon as a small amount of gate current is given to the base of transistor Q2 by applying forward bias to its base-emitter junction, it generates the collector current as ? times the base current. This collector current of Q2 is fed as input base current to Q: which is further multiplied by ? 1 times as ICl which forms input base current of Q2 and undergoes further amplification. In this way both transistors feedback each other and the collector current of each goes on multiplying. This process is very quick and soon both the transistors drive each other to saturation. Now the device is said to be in. on-state. The current through the on-state SCR is controlled by external impedance only. How Scr Works Analysis Essay Example How Scr Works Analysis Essay How an SCR works? -Principle of Operation SCR Working Principle The SCR is a four-layer, three-junction and a three-terminal device and is shown in fig. a. The end P-region is the anode, the end N-region is the cathode and the inner P-region is the gate. The anode to cathode is connected in series with the load circuit. Essentially the device is a switch. Ideally it remains off (voltage blocking state), or appears to have an infinite impedance until both the anode and gate terminals have suitable positive voltages with respect to the cathode terminal. The thyristor then switches on and current flows and continues to conduct without further gate signals. Ideally the thyristor has zero impedance in conduction state. For switching off or reverting to the blocking state, there must be no gate signal and the anode current must be reduced to zero. Current can flow only in one direction. In absence of external bias voltages, the majority carrier in each layer diffuses until there is a built-in voltage that retards further diffusion. Some majority carriers have enough energy to cross the barrier caused by the retarding electric field at each junction. These carriers then become minority carriers and can recombine with majority carriers. Minority carriers in each layer can be accelerated across each junction by the fixed field, but because of absence of external circuit in this case the sum of majority and minority carrier currents must be zero. A voltage bias, as shown in figure, and an external circuit to carry current allow internal currents which include the follow ¬ing terms: The current Ix is due to †¢Majority carriers (holes) crossing junction J1 †¢Minority carriers crossing junction J1 Holes injected at junction J2 diffusing through the N-region and crossing junc ¬tion J1 and †¢Minority carriers from junction J2 diffusing through the N-region and crossing junction J1. Similarly I2 is due to six terms and I3 is due to four terms. The two simple analogues to explain the basic action for the thyristor are those of the diode and the two transistor models. 1. 1. Diode Model. The thyristor is similar to three d iodes in series as there are three P-N junctions. Without gate bias, there is always at least ne reverse biased junction to prevent conduction irrespective of the polarity of an applied voltage between anode and cathode. If the anode is made positive and the gate is also biased positively with respect to cathode, the P-layer at the gate is flooded by the electrons from the cathode and loses its identity as a P-layer. Accordingly the thyristor becomes equivalent to a conducting diode. Scr working 1. 2. Two Transistor Model. Imagine the SCR cut along the dotted line, as shown in fig. a. Then we can have two devices, as shown in fig. b. We will write a custom essay sample on How Scr Works Analysis specifically for you for only $16.38 $13.9/page Order now We will write a custom essay sample on How Scr Works Analysis specifically for you FOR ONLY $16.38 $13.9/page Hire Writer We will write a custom essay sample on How Scr Works Analysis specifically for you FOR ONLY $16.38 $13.9/page Hire Writer These two devices can be recognized as two transistors. The upper left one is P-N-P transistor and the lower right N-P-N type. Further it can be recognized that the base of the P-N-P transistor is joined to the collector of the N-P-N transistor while the collector of P-N-P is joined to the base of N-P-N transistor, as illustrated in fig. c. The gate terminal is brought out from the base of the N-P-N material. This construction has been conceived merely to explain the working of SCR, otherwise in physical shape the SCR has four solid layers of P-N-P-N type only. Now we can see that the two transistors are connected in such a manner that the collector of Q1 is connected to the base of Q2 i. e. the output collector current of Qt becomes the base current for Q2. In the similar way the collector of Q2 is joined to the base of Q1 which shows that the output collector current of Q2 is fed to Q1 as input base current. These are back to back connections of transistors in such a way that the output of one goes into as input of other transistor and vice-versa. This gives net gain of loop circuit as ? 1 x ? 2 where ? 1 and ? are current gains of two transistors respectively. When the gate current is zero or the gate terminal is open, the only current in circulation is the leakage current, which is very small in case of silicon device specially and the total current is a little higher than sum of individual leakage currents. Under these conditions P-N-P-N device is said to be in its forward blocking or high impedance ‘off state. As soon as a small amount of gate current is given to the base of transistor Q2 by applying forward bias to its base-emitter junction, it generates the collector current as ? times the base current. This collector current of Q2 is fed as input base current to Q: which is further multiplied by ? 1 times as ICl which forms input base current of Q2 and undergoes further amplification. In this way both transistors feedback each other and the collector current of each goes on multiplying. This process is very quick and soon both the transistors drive each other to saturation. Now the device is said to be in. on-state. The current through the on-state SCR is controlled by external impedance only.

Biography of Henrietta Muir Edwards

Biography of Henrietta Muir Edwards A legal expert, Henrietta Muir Edwards spent her long life advocating for the rights of women and children in Canada. Her accomplishments included opening, with her sister Amelia, the Working Girls Association, a forerunner of the YWCA. She helped found the National Council of Women of Canada and the Victorian Order of Nurses. She also published the first magazine for working women in Canada. She was 80 in 1929 when she and the other Famous Five women finally won the Persons Case which recognized the legal status of women as persons under the BNA Act, a milestone legal victory for Canadian women. Birth Dec. 18, 1849, in Montreal, Quebec Death Nov. 10, 1931, in Fort Macleod, Alberta Causes of Henrietta Muir Edwards Henrietta Muir Edwards supported many causes, especially those involving the legal and political rights of women in Canada. Some of the causes she promoted were temperanceraising the age of consentequal grounds for divorceequal parental rightsmothers allowancesreform of the prison system in Canada. The career of Henrietta Muir Edwards: In Montreal Henrietta Muir, with her sister Amelia, founded the Working Girls Association, a forerunner of the YWCA in 1875.She launched and edited Womens Work in Canada, the first Canadian magazine for working women.In 1883, Henrietta Muir Edwards moved with her husband and three children to Saskatchewan.She was involved with the Womans Christian Temperance Union (WCTU) from 1886.With Lady Aberdeen, the wife of the Governor General of Canada, Henrietta Muir Edwards started the National Council of Women in 1893. Henrietta Muir Edwards worked with the organization for more than 30 years.Again with Lady Aberdeen, Henrietta Muir Edwards helped found the Victorian Order of Nurses in 1897.Henrietta Muir Edwards and her family moved to Alberta in 1903.In 1908, Henrietta Muir Edwards compiled a summary of Canadian federal and provincial laws relating to women and children.She wrote handbooks on women and Canadian law - Legal Status of Women in Canada in 1917 and Legal Status of Women in Alb erta in 1921. Henrietta Muir Edwards was one of the Famous Five in the Persons Case which established the status of women as persons under the BNA Act in 1929. See Also: Emily MurphyNellie McClungLouise McKinneyIrene Parlby