Consider the three-terminal voltage regulator in Figure 15.51, with Zener diode voltages of \(V_{Z}=6.3 \mathrm{~V}\). Assume transistor parameters of \(V_{B E}(\mathrm{npn})=\) \(V_{E B}(\mathrm{pnp})=0.6 \mathrm{~V}\), and neglect base currents.

(a) Determine resistance \(R_{4}\) such that \(I_{Z 2}=0.25 \mathrm{~mA}\).

(b) Determine \(R_{12}\) such that \(V_{O}=12 \mathrm{~V}\).

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Q16 15 RA D Di Q5 29 23 R3=> 576 R = 3.4 214 R = 3.9 R => 5.8 DAK D3 R14= 5 210 R15= 100 212 ww 213 28 26 HH C = 5pF Q2 R = R6= 17.8 2.84 V+ Q11 www R11= 1.9 www Vo R12 R13= 2.23 Ground Startup Reference voltage Error amp. Figure 15.51 Equivalent circuit, LM78LXX series three-terminal positive voltage regulator Current amp.