lectureslides11

Lectureslides11

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Unformatted text preview: loses at t = 0. Interesting things start tp happen. t=0 IS R iL + L vL – 1. Because the through an inductor cannot change instantaneously, iL will maintain the value that it had initially. iL (t = 0) = iLi (= 0). 2. Inductor voltage current has no such restriction, and it’s value will instantaneously jump to a value determined by the voltage across the parallel resistor. vL (t = 0) = vR = IS R EE 442 RC and RL transients – 16 As we observe how the situation progresses for t > 0: t>0 IS R iL increasing + L vL decreasing – 3. Current will begin to flow into the inductor so iL (t > 0) > iLi, (> 0) (and increasing). 4. As the inductor takes more of the current from the source, less current flows through the resistor, and the voltage across the inductor (and inductor) drops. (We might say that the inductor is becoming “amped up”.) EE 442 RC and RL transients – 17 IS R iL = IS + L vL = 0 – after a sufficiently long time 5. Eventually, the inductor current will increase until it is equal to IS – it is taking all of the current from the source. Since no current is left to go through the resistor, the parallel voltage drops to zero. From that time nothing changes anymore. This is a transient effect. Initially, the inductor current was at some fixed, steady value ( = 0 in our example) and the inductor voltage was zero. When the switch closed, the voltage jumped up to a value determined the initial voltage across the resistor. The voltage across the inductor caused the inductor to begin increasing from its initial value. When the inductor current equaled the source current, the voltage dropped to zero, and the circuit returned to a static (quiescent) state with the inductor having a new, higher current, with no voltage across it. EE 442 RC and RL transients – 18 IS R iL (t) + L vL (t) – Now, let’s do the math. For t > 0 (after the switch has closed): vR = vL vR = (IS − iL ) R diL vL = L dt diL ( I S − iL ) R = L dt Another differential equation. This is pret...
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This document was uploaded on 04/05/2014.

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