11. A diode match finder circuit has an input voltage of 2.6v and an output voltage is 5.78v. Calculate the voltage drop across diode 1N4735
A. 2.22v
B. 8.38v
C. 3.18v
D. 15.02v
Answer: C
The output voltage Vo =Vin+ VD.
∴ the voltage drop across 1N4735, VD =Vo – Vin = 5.78-2.6 =3.18v.
12. Find the voltage drop across the zener diode in the zener diode tester from the given specifications: IZk=1mA, VZ =6.2v, input voltage= 1.2v, output voltage =3.2v and resistance in series with meter =150Ω.
A. 6.2mA
B. 8mA
C. 21.33mA
D. Cannot be determined
Answer: A
Current through the zener
Io=Vin/R1 =1.2v/150Ω =8mA.
Since Io > IZk the voltage across the zero will be approximately equal to 6.2v. As the current is larger than the knee current (IZk) of the Zener, it blocks VZ volts.
13. Which among the following is preferred to display devices in digital applications?
A. Matched Zener diode
B. Matched LEDs
C. Matched rectifier diode
D. All of the mentioned
Answer: B
Matched LEDs with equal brightness at a specific value of current are useful as indicators and display devices in digital applications.
14. The maximum current through the load in all application that uses voltage to current converter with floating is
A. 100mA
B. 75mA
C. 25mA
D. 50mA
Answer: C
The maximum current through the load cannot exceed the short circuit current of the 741c op-amp which is 25mA.
15. For voltage to current converter with grounded load, establish a relation between the non-inverting input terminals and load current
A. V1 = [Vin+Vo-(IL×R)] /2
B. V1 = [Vin-Vo-(IL×R)] /2
C. V1 = [Vin+Vo-IL+R] /2
D. V1 = [Vin+Vo+(IL×R)] /2
Answer: A
In the voltage to current converter circuit, the relationship between the voltage v1 at the non-inverting input terminal and load is given as
V1 = [Vin+Vo-(IL×R)] /2.
16. Find the gain of the voltage to the current converter with grounded load?
A. 2
B. 1
C. ∞
D. 0
Answer: A
In voltage to current converter with a grounded load all resistors must be equal in value.
∴ Gain = Vo/Vin
= [1+(RF/R1)] = 1+R/R =1+1=2.
17. Find the output voltage and the load current for the circuit given below. Assume that the op-amp is initially nulled V1 =2.5v
A. IL=0.42mA, Vo =10v
B. IL=0.42mA, Vo =3.4v
C. IL=0.42mA, Vo =6.1v
D. IL=0.42mA, Vo =5v
Answer: D
The load current IL =vin /R
=5/12kΩ =0.42mA
vo =IL×R, can be obtained when
Vo=2×V1 = 2×2.5 =5v.
18. Determine the maximum value of output current of the DAC in MC1408?
A. 0.773×(Vref/R1)
B. 0.448×(Vref/R1)
C. 0.996×(Vref/R1)
D. 0.224×(Vref/R1)
Answer: C
The output current of DAC is the maximum when all the inputs are logic 1.
A. 0 – 2.51v
B. 0 – 2.22v
C. 0 – 3.74v
D. 0 – 4.93v
Answer: D
When all binary input D0 through D7 are logic 0, the current Io =0.
∴ The minimum value of Vo =0v.
When all the inputs are at logic 1, Io = (Vref/R1) ×
(1/2+1/4+1/8+1/16+1/32+1/64+1/128/+1/256)
= (3/2kΩ) × (0.996) =1.494mA.
Hence, the maximum value of output voltage is
Vo= Io×RF = 1.494×3.3kΩ =4.93v.
Thus, the output voltage range is from 0 to 4.93v.
20. Calculate the change in the output voltage if the photocell is exposed to a light of 0.61lux from a dark condition. Specification: Assume that the op-amp is initially nulled, Minimum dark resistance = 100kΩ, and resistance when illuminated (at 0.61lux) = 1.5kΩ.
A. Vo –> 23v to 50v
B. Vo –> 0v to 33.11v
C. Vo –> -1.653v to 8.987v
D. Vo –> -0.176v to -11.73v
Answer: D
The resistance RT in darkness is 100kΩ.
The minimum output voltage in darkness is
Vo min = -(Vdc×RF)/ RT
= -(3.2v×5.5kΩ)/100kΩ = -0.176v.
When the photocell is illuminated, its resistance RT =1.5kΩ.
Therefore, the maximum output voltage is
Vo max = -(Vdc×RF)/ RT
= -(3.2v×5.5kΩ)/1.5kΩ =-11.73v.
Thus, Vo varies from -0.176v to -11.73 as the photocell is exposed to light from a dark condition.
21. Which cell can be used instead of a photocell to obtain an active transducer in photosensitive devices?
A. Photovoltaic cell
B. Photodiode
C. Photosensor
D. All of the mentioned
Answer: A
A photovoltaic cell is a semiconductor junction device that converts radiation energy into electrical energy and hence it does not require external voltage.
