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

1. 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

   
   
   

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1. View Hint View Answer Discuss in Forum

   The given circuit (i.e., fig)
   

   From figure, VZ = VL = Vi(min) ×	2K
   	2K + 0·25K

   
   

   or 20 = Vi(min) ×	2
   	2·25

   
   

   or Vi(min) = 20 ×	2.25	= 22·5V
   	2

   
   Given, I_ZM = I_Z(max) = 50 mA
   

   IL =	20	= 10 mA
   	2K

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

   Since, IS(max) =	Vi(max) – VZ
   	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.

   
   

   Correct Option: B

   The given circuit (i.e., fig)
   

   From figure, VZ = VL = Vi(min) ×	2K
   	2K + 0·25K

   
   

   or 20 = Vi(min) ×	2
   	2·25

   
   

   or Vi(min) = 20 ×	2.25	= 22·5V
   	2

   
   Given, I_ZM = I_Z(max) = 50 mA
   

   IL =	20	= 10 mA
   	2K

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

   Since, IS(max) =	Vi(max) – VZ
   	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.

   
   

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237. In a voltage regulator network with fixed R_L and R, what element dictates the minimum level of source voltage?

1. 1. V_Z

   
   
   

   2. I_Z

   
   
   

   3. I_ZM

   
   
   

   4. None of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   In a voltage regular network with fixed R_L and R
   ∴ I = or V_i = I R + V_Z
   Thus, V_Z dictates the minimum level of source voltage.

   Correct Option: A

   In a voltage regular network with fixed R_L and R
   ∴ I = or V_i = I R + V_Z
   Thus, V_Z dictates the minimum level of source voltage.

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238. With this Zener diode in its ‘‘on state’’. What is the level of I_Z for the maximum load resistance?
     
     
     

1. 1. 0 mA

   
   
   

   2. Undefined

   
   
   

   3. Equal to I_RL

   
   
   

   4. I_ZM

   
   
   

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1. View Hint View Answer Discuss in Forum

   Since given that Zener diode in its ‘ON’ state
   so, V_L = V_Zv = 10 V
   

   IR =		Vi – VZ	=	(50 – 10) V	= 40 mA
   		R		1 kΩ

   
   I_L(min) = I_R – I_ZM = 40 – 32 = 8 mA
   We know that for maximum load resistance load current should be minimum i.e.
   

   RL(max) =	VZ
   	IL (min)

   
   Hence I_Z should be equal to I_ZM.

   
   

   Correct Option: D

   Since given that Zener diode in its ‘ON’ state
   so, V_L = V_Zv = 10 V
   

   IR =		Vi – VZ	=	(50 – 10) V	= 40 mA
   		R		1 kΩ

   
   I_L(min) = I_R – I_ZM = 40 – 32 = 8 mA
   We know that for maximum load resistance load current should be minimum i.e.
   

   RL(max) =	VZ
   	IL (min)

   
   Hence I_Z should be equal to I_ZM.

   
   

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239. Calculate I_L and I_Z.—
     
     
     

1. 1. 2 mA, 0 mA

   
   
   

   2. 4 mA, 2 mA

   
   
   

   3. 2 mA, 2 mA

   
   
   

   4. 2 mA, 4 mA

   
   
   

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1. View Hint View Answer Discuss in Forum

   First step to check whether zener diode in breakdown mode or not
   

   VL = V i		5K	=	16 × 5	13.33V
   		5k + 1 kΩ		6

   
   ∴ V_L > V_Z, So Zener diode in break down mode
   Therefore,
   

   IL =		VL	=	VZ	=	10V
   		RL		RL		5 kΩ

   
   or I_L = 2mA
   

   I =		Vi – VZ	=	16 – 10	= 6 mA
   		R		1 kΩ

   
   Now, I_Z = I – I_L = 6 – 2 = 4mA.
   Hence alternative (D) is the correct choice.

   
   

   Correct Option: D

   First step to check whether zener diode in breakdown mode or not
   

   VL = V i		5K	=	16 × 5	13.33V
   		5k + 1 kΩ		6

   
   ∴ V_L > V_Z, So Zener diode in break down mode
   Therefore,
   

   IL =		VL	=	VZ	=	10V
   		RL		RL		5 kΩ

   
   or I_L = 2mA
   

   I =		Vi – VZ	=	16 – 10	= 6 mA
   		R		1 kΩ

   
   Now, I_Z = I – I_L = 6 – 2 = 4mA.
   Hence alternative (D) is the correct choice.

   
   

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240. In the breakdown region, a Zener diode behaves like a—

1. 1. Constant voltage source

   
   
   

   2. Constant current source

   
   
   

   3. Constant resistance source

   
   
   

   4. None of the above
      

   
   
   

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1. View Hint View Answer Discuss in Forum

   In the breakdown region, a zener diode behaves like a constant voltage source.
   

   Correct Option: A

   In the breakdown region, a zener diode behaves like a constant voltage source.
   

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