Question

*4.57 Consider the voltage-regulator circuit shown in Fig. P4.57. The value of R is selected to obtain an output voltage Vo (across the diode) of 0.7 V. Figure P4.57 (a) Use the diode small-signal model to show that the change in output voltage corresponding to a change of 1 V in Vt is AV AV: = v* +-0.7 V+ V++V, -0.7 This quantity is known as the line regulation and is usually expressed in mV/V. (b) Generalize the expression above for the case of m diodes connected in series and the value of R adjusted so that the voltage across each diode is 0.7 V (and Vo=0.7mV). (C) Calculate the value of line regulation for the case V+ = 10 V (nominally) and (i) m= 1 and (ii) m = 3.

Answer 1

Avoid but id = 1 1 1 1 avt - Rtrd Substituting in the above Equations DVO - HIV Avt Aut R+V/I + IR 17/I ''IR=V*-0.7 There b) DVO mid Aut Rt mod #VERT NdPy Substituting in aboue Equation Ako - MV4/I - My R+ m /1 IR + M V where pe: vt_m60.7): substituting above as c) when m=1 when m=3 0:25 +4-0.7 9 +0-25-8.7 - 0825 Jot.025-0.7 Duit = 2.68muſy V2-0-7 Jyo = 9.41m vly Avt