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Unformatted text preview: ECE 137A Quiz #2 Solution Luis Chen Here, we assume ideal diode, i.e. No reverse current. Initially, E i = 1 2 C ⋅ V C 2 At t>0, switch closes, charges flow from the capacitor to the diode. The diode is reverse biased, and has depletion capacitance C depl . To calculate, Ef, we need to find Vo(t) in steady state (Vf). Q i = C V C Q f = Q i = C C Depl V f C V C = C C Depl V f so V f = Vc C C C Depl where C Depl = C j0 1 − V f / i , C j0 = q s 2 i Na ⋅ Nd Na Nd V f = Vc C C C j0 1 − V f / i Vf is difficult to solve symbolically, Had we been given the values of C, Vc and Area, then we can solve it easily. Let's take some numbers and see what we get, Assume C=20fF, Vc=1V, and A=1e-6 cm^2, Vc>0 t=0+ C Na=10 17 Nd=10 15 Lossless switch Vo(t)=0 for t<0 1. Calculate total energy before switch closes 2. Calculate total energy after switch closes 3. Is Ei=Ef, if not, why not Vo(t)...
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- Winter '08
- Calculate total energy, C Depl V, C C Depl