4.58 Consider the voltage-regulator circuit shown in Fig P4.57 under the condition that a load current IL is drawn from the output terminal.
(a) If the value of IL is sufficiently small that the corresponding change in regulator output voltage ∆VO is small enough to justify using the diode small-signal model, show that
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 ID, show that the expression derived in (a) becomes
Select the lowest possible value for ID that results in a load regulation whose magnitude is ≤ 5mV/mA. If V+ is nominally 10 V, what value of R is required? Also, specify the diode required in terms of its IS.
(c) Generalize the expression derived in (b) for the case of m diodes connected in series and R adjusted to obtain VO = 0.7m V at no load.
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