# 18 - 13-Jun-11-7:10 PM More RL RC Circuits EEL 3111...

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13-Jun-11---7:10 PM More RL & RC Circuits 1 University of Florida, EEL 3111 – File # 18 © Dr. Eric M. Schwartz EEL 3111: Circuits 1 RL and RC Circuits Revisited Today’s Menu Another Look at Time Constants Generalizing voltage or current in RL or RC circuit >Examples Single Capacitor/Single Inductor Today’s Class . .. University of Florida, EEL 3111 –File # 18 © Dr. Eric M. Schwartz 1 Circuit analysis > Examples finding things other than i L (t) and v C (t) See examples on web-site: OMalley133, BBarricade OMalley137, OMalley137a, RC_Switch0, RC_Switch1, RL_Switch1, OMalley136, RL_Switch2, RLC0 EEL 3111: Circuits 1 RC Example + L R i t i ) 0 ( i R t > 0 OMalley133.sch v(t) - i L  t L R L L L L TH e i i i t i ) ( ) 0 ( ) ( ) ( L i t v 3 ) 0 ( University of Florida, EEL 3111 –File # 18 © Dr. Eric M. Schwartz 2 open switch After 3 0 ) ( TH L R i open switch Before A 2 5 10 ) 0 ( L i 0 A, 2 ) ( 2 3 t e t i t L Final Answer 0 V, 6 ) ( 5 . 1 t e t v t NOT !

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13-Jun-11---7:10 PM More RL & RC Circuits 2 University of Florida, EEL 3111 – File # 18 © Dr. Eric M. Schwartz EEL 3111: Circuits 1 RL and RC Circuits Revisited = time constant: = L/R or = R C  0 , e ) ( ) 0 ( ) ( ) ( t x x x t x t = time constant: = L / R TH or = TH Switching at time t = 0. R TH is the Thévenin resistance “seen” by the L or C AFTER the switching Find x (0) before t =0 by dc analysis, L as a short or C as an open circuit. ) ( or (t) either ) ( t v i t x C L University of Florida, EEL 3111 –File # 18 © Dr. Eric M. Schwartz 3 Find x ( ) by dc analysis, L as a short or C as an open circuit. DC Sources Dependent Sources Resistors and Switches + v C - a b i L EEL 3111: Circuits 1 RC Circuit Example The inside of Bob’s Barricade probably looks like this When voltage is “low” >The resistance is extremely high BBarricade.sch probably looks like this: >No light occurs When the voltage reaches a critical “high” value >The light goes on >The device suddenly has a low resistance nonlinear element: called a University of Florida, EEL 3111 –File # 18 © Dr. Eric M. Schwartz 4 nonlinear element: called a Relaxation Oscillator . When voltage across the light gets “high,” the light suddenly has a low resistance (and the C discharges). v C t
13-Jun-11---7:10 PM More RL & RC Circuits 3 University of Florida, EEL 3111 – File # 18 © Dr. Eric M. Schwartz EEL 3111: Circuits 1 Another RC Circuits Example Timers also have this type of RC_Switch0.sch circuit: > Close to start time measurements > Open to stop time measurements > Voltage on capacitor is a measure of the time University of Florida, EEL 3111 –File # 18 © Dr. Eric M. Schwartz 5 Sawtooth wave operation > Initial part is almost a straight line

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18 - 13-Jun-11-7:10 PM More RL RC Circuits EEL 3111...

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