For the Zener regulator circuit shown below, the range of

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For the Zener regulator circuit shown below, the range of input voltage for the Zener diode to remain in ‘ON’—

1. 20 V < V_i < 25 V
2. 22·5 V < V_i < 35 V
3. 22·5 V < V_i < 25 V
4. None of these

Correct Option: B

The given circuit (i.e., fig)

From figure, V_Z = V_L = V_i(min) ×	2K
	2K + 0·25K

or 20 = V_i(min) ×	2
	2·25

or V_i(min) = 20 ×	2.25	= 22·5V
	2

Given, I_ZM = I_Z(max) = 50 mA

I_L =	20	= 10 mA
	2K

I_S(max) = I_Z(max) + I_L
= 50 mA + 10 mA = 60 mA

Since, I_S(max) =	V_i(max) – V_Z
	0·25 Kπ

or V_i(max) = I_S(max) × 0·25 Kπ + V_Z = 60 mA × 0·25 Kπ + 20 V
or V_i(max) = 15V + 20V = 35V
Therefore the range of input voltage 22·5V < Vi < 35V
Hence alternative (B) is the correct choice.