1. The abbreviation PIV in the case of a diode stands for ____________
a) Peak Inferior Voltage
b) Problematic Inverse Voltage
c) Peak Inverse Voltage
d) Peak Internal Voltage
Explanation: PIV stands for Peak Inverse Voltage. It is the maximum reverse bias voltage which a diode can bear without breakdown.
2. What is meant by the PIV rating of a diode?
a) Maximum reverse bias potential which can be applied across a diode without breakdown
b) Maximum forward bias potential which can be applied across a diode without breakdown
c) Minimum potential required by a diode to reach conduction state
d) Maximum power allowable to a diode
Explanation: PIV rating indicates the maximum allowable reverse bias voltage which can be safely applied to a diode. If a reverse potential is greater than PIV rating then the diode will enter reverse breakdown region.
3. The voltage after which the diode current exponentially increases with forward bias is not known as ________
a) Offset voltage
b) Threshold potential
c) Firing potential
d) Peak forward voltage
Explanation: The voltage after which a diode increases rapidly is known as the offset voltage, threshold voltage, firing potential and cut-in voltage. Beyond this voltage, the forward bias voltage overcomes the potential barrier and rapid conduction occurs.
4. The diode current equation is not applicable in ____________
a) Forward biased state
b) Reverse biased state
c) Unbiased state
d) It is applicable in all bias states
Explanation: Diode equation is I=IO(eqV/kT – 1). It is applicable in all bias condition that is forward, reverse and unbiased states.
5. Emission coefficient of Germanium is ___________
a) 1
b) 1.1
c) 1.5
d) 2
Explanation: Emission coefficient or ideality factor accounts the effect of recombination taking place in the depletion region. The range of factor is from 1 to 2. For Germanium it is 1.
6. The ideality factor of Silicon is ___________
a) 1
b) 2
c) 1.3
d) 1.7
Explanation: Emission coefficient or ideality factor accounts the effect of recombination taking place in the depletion region. The range of factor is from 1 to 2. For silicon it is 2.
7. What is the value of the voltage equivalent of temperature at room temperature (27oC)?
a) 26mV
b) 36mV
c) 0.26mV
d) 260mV
Explanation: Voltage equivalent of temperature VT is equal to the product of Boltzman constant (J.K-1) and temperature in Kelvin. At a temperature of 27°C, it’s value is VT=KT/q=26mV.
8. What happens to cut-in voltage when the temperature increases?
a) Cut-in voltage increases
b) Cut-in voltage decreases
c) Cut-in voltage either increases or decreases
d) Cut-in voltage doesn’t depend on temperature
Explanation: As temperature increases the conductivity of a semiconductor increases. The diode conducts smaller voltage at larger temperature. Therefore, cut-in voltage decreases.
9. When temperature increases, reverse saturation current _________
a) Increases
b) Decreases
c) Doesn’t depend on temperature
d) Either increases or decreases
Explanation: As temperature increases the conductivity of a semiconductor increases. Reverse saturation current increases as temperature increases.
10. Calculate the forward bias current of a Si diode when forward bias voltage of 0.4V is applied, the reverse saturation current is 1.17×10-9A and the thermal voltage is 25.2mV.
a) 9.156mA
b) 8.23mA
c) 1.256mA
d) 5.689mA
Explanation: Equation for diode current
I=I0×(e(V/ηVT)-1) where I0 = reverse saturation current
η = ideality factor
VT = thermal voltage
V = applied voltage
Since in this question ideality factor is not mentioned it can be taken as one.
I0 = 1.17 x 10-9A, VT = 0.0252V, η = 1, V = 0.4V
Therefore, I = 1.17×10-9xe0.4/0.025 -1 = 9.156mA.