*4.55 Consider the voltage-regulator circuit shown in Fig P4.54 under the condition that a load current I L is drawn from the output terminal. (a) If the value of I L is sufficiently small that the corre- sponding change in regulator output voltagefiV O is small enough to justify using the diode small-signal model, show that fiV O I L = − r d ∫R This quantity is known as the load regulation and is usually expressed in mV/mA. (b) If the value of R is selected such that at no load the voltage across the diode is 0.7 V and the diode current is I D , show