Notes on Thevenin and Norton Equivalent Circuits | ECE 3710, Study notes of Electrical and Electronics Engineering

Download Notes on Thevenin and Norton Equivalent Circuits | ECE 3710 and more Study notes Electrical and Electronics Engineering in PDF only on Docsity! Thevenin and Norton Equivalent Circuits ECE 3710, Fall 2011 Georgia || Gollege of Tech ||| Encineering & School of Electrical and Computer Engineering Text  Key   2   Sec@on  2.6  in  the  book   Short  Circui@ng  a  Thevenin  Equivalent   5   +   –  Vt   isc   Rt   isc = Vt Rt The  “short  circuit”  current   We  can  build  the  Thevenin  Equivalent  Circuit  by  knowing  the   “open  circuit  voltage”  and  the  “short  circuit  current”!   Finding  Voc  and  Isc   6   +   –   10V   10Ω   60Ω   +   –   Voc   Voc = 60 10+ 60 10V = 8.6V isc   isc   isc = 10V 10! =1A Zeroing  the  Sources  to  get  Rt   7   +   –  Vt   Rt   Zero  the  voltage  source  (short  it)  and  look  into   the  terminals  to  find  Rt   Example  (Zeroing  Sources)   10   +   –  4V   50Ω   10Ω   1A   isc   i1   What  can  we  say  about  the  current  i2?   i2   i1 = 4 50 = .08A isc = i1 +1=1.08A Thevenin  Equivalent  with  Dep.  Sources   11   2A   50Ω   10Ω   Vx   +   -­‐  .5Vx   We  cannot  find  the  Thevenin  Equivalent  resistance  by  zeroing  the   sources  in  a  circuit  with  dependent  sources!   +   –   Thevenin  Equivalent  with  Dep.  Sources   12   2A   50Ω   10Ω   Vx   +   -­‐  .5Vx   Start  with  the  open  circuit  voltage   Voc   +   –   +   –   Vx = 2(50) =100V Dep. Source = .5(100) = 50V Voc = 50V Norton  Equivalent  Circuit   15   In   Rt   A  Norton  Equivalent  circuit  consists  of  an  independent   current  source  in  parallel  with  the  Thevenin  resistance   Short  Circuit  of  a  Norton  Equivalent   16   In   Rt   isc   isc = In This  is  the  same  short  circuit  current  that   we  found  for  the  Thevenin  Equivalent   Step-­‐by-­‐Step  for  Equivalent  Circuits   •  Start  by  determining  either  the  open  circuit   voltage  (Voc)  or  the  short  circuit  current  (isc)   •  Zero  the  independent  sources  and  look  back   into  the  terminals  to  find  the  Thevenin   resistance  (Rt)   •  Use  the  Rt  and  either  Voc  or  isc  to  compute  the   remaining  value   •  Draw  either  the  Thevenin  or  Norton   Equivalent  Circuit   17   Source  Transforma@on  Example   20   +   –  30V   1Ω   V   i1   Lets  start  by  transforming  the  Norton  into  a  Thevenin   R   +   –   R =10! V =10(2) = 20V i1= (30V ! 20V ) 11" = .9A Source  Transforma@on  Example   21   +   –  30V   1Ω   10Ω   2A   i1   i2   The  leH  side  of  the  circuit  responds  the  same,  regardless  of  what   equivalent  circuit  we  have  on  the  right   i2 = i1 + 2A = 2.9A Source  Transforma@on  Example   22   +   –  30V   1Ω   10Ω   2A   i1   i2   Solve  the  for  i1  and  i2  using  a  source  transforma@on   Lets  now  try  transforming  the  Thevenin  to  a  Norton