The line regulation of a reference diode D2 can be improved dramatically if we precede it by another reference diode D1, as depicted in Fig. P1.78. Clearly, for the circuit to work properly, VZ1 must...

The line regulation of a reference diode D2 can be improved dramatically if we precede it by another reference diode D1, as depicted in Fig. P1.78. Clearly, for the circuit to work properly, VZ1 must be suffi ciently larger than VZ2, say by at least 30% or so, and the resistances R1 and R2 must be small enough to guarantee that each diode remains in the BD region under all possible line and load conditions. (a) If D1 is a 10-V Zener diode with rz1 5 15 V, and D2 is a 6.2-V Zener diode with rz2 5 10 V, fi nd the line and load regulation (in mV/V and mV/mA) if VI 5 18 V, R1 5 1 kV, R2 5 0.75 kV, and IL 5 2 mA. (b) To appreciate the benefi ts brought about by D1, suppose we pull D1 out of the circuit, while leaving everything else the same. How is the line regulation affected? How is the load regulation affected?