Question

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3(C) [8 marks] R1 w R2 Vo(t) Vin(t) Figure Q3C Consider the circuit in Figure Q3c. The Zener diode is rated 12V and 4.8mW. Vin=60V. R1=60k22. (i) Find the minimum resistance, R2, for which regulation can be obtained [3 marks] Find the maximum resistance, R2, for which regulation can be obtained. [5 marks]

Answer 1

Answer: IS VIR VIL" I R, VOLE Vintti zener diode? giren data Vin = 60v R = 60K12 P2 = 4.8 mW = 4.8x1o? Watte ( max. Zener power) V2 = 12v (maximum Pener voltage) Iz(max) = Iz(max) = 4.8x10 Ta = 0.4x1o? A Iz(max) = 0.4mA Iz (min) (i) IZ( min ) = 0 mA .... becauwe ſnot given in the problem, To find minimum resistanu R2, cument Iz Showa be maximum 10l from the ott diagram. - Is = Iz + Iq but Is e Vin - VZ 60-12 60km

Is = us ma - 60 Is = 0.8 mĄ find minimum R to It should be minimum.ie 220 Is - Iz(min) + Ig( max) Facmax) = 0.8 mm VZ R2 (min) = - Ilmax) 12 0.8x10² - 15*10's R2 (min) = 1560 in to find max. resistance Rz, cument in the sener diode should be maximum and Ia cument should be minimum. Is = Izcmax) + Salmin) 0.8mA = 0.4mA + Il min) Izl min) - (0.8 -0.4)ma Iacmin) = o-uma

Ne R2(max) Izl min) la 0.4MA 0.4 E x100 = 30x10's R2(max) = 30 km