Electronic Devices and Circuits Questions and Answers – Transistor Hybrid Model

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Transistor Hybrid Model”.

1. The h-parameters analysis gives correct results for __________
a) large signals only
b) small signals only
c) both large and small
d) not large nor small signals

Explanation: Every linear circuit is associated with h –parameters. When this linear circuit is terminated with load rL, we can find input impedance, current gain, voltage gain, etc in terms of h-parameters. For small a.c. signal, transistor behaves as linear device. Under such circumstances the a.c. signal operation of a transistor can be described in terms of h-parameters.

2. For what type of signals does a transistor behaves as linear device?
a) small signals only
b) large signals only
c) both large and small signal
d) no signal

Explanation: The small variation in the total voltage and current due to an application of signal moves the point up and down just by a bit and that whole up and down dynamics of the operating point from its DC value point can be approximated to be along a straight line. Whole analysis can be done with same assumption of linearity with the limit of signal being in the same vicinity of the DC operating point.
That’s how we get all those equations for linear operation and also its small signal equivalent model using h-parameters.

3. How many h-parameters are there for a transistor?
a) two
b) three
c) four
d) five

Explanation: A transistor has four h-parameters –
H11 = V1/i1 (Input Impedance with output short circuited)
H21 = i2/i1 (Current gain with output short circuited)
H12 = V1/V2 (Voltage gain with feedback ratio with input terminals open)
H22 = i2/V2 (Output Admittance with input terminals open).

4. The dimensions of hie parameters are _______
a) MHO
b) OHM
d) Ampere

Explanation: hie = vBE/ib; common emitter input impedance
For VCE = 0 i.e. output short circuited
Where vBE = Base emitter voltage i.e. input voltage
ib = Base current i.e. input current
We know that V/I = R. Its unit is ohm.

5. The hfe parameter is called _______ in CE arrangement with output short circuited.
a) Voltage Gain
b) Current gain
c) Input impedance
d) Output impedance

Explanation: hfe in CE arrangement is given as
Hfe = Ic/Ib for VCE = 0 short circuited
So, this is current gain as it is then output to input current ratio.
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6. What happens to the h parameters of a transistor when the operating point of the transistor changes?
a) It also changes
b) Does not change
c) May or may not change
d) Nothing happens

Explanation: It is very difficult to get exact values of h parameters for a particular transistor. It is because these parameters are subject to considerable variation unit to unit variation, variation due to change in temperature and variation due to the operating point.

7. If temperature changes, h parameters of a transistor _____
a) also change
b) does not change
c) remains same
d) may or may not change

Explanation: It is very difficult to get exact values of h parameters for a particular transistor. It is because these parameters are subject to considerable variation unit to unit variation, variation due to change in temperature and variation due to the operating point.

8. In CE arrangement, the value of input impedance is approximately equal to _____
a) HIE
b) HIB
c) HOE
d) HRE

Explanation: hie = vBE/ib; common emitter input impedance
For VCE = 0 i.e. output short circuited
Where vBE =Base emitter voltage i.e. input voltage
ib = Base current i.e. input current.

9. How many h-parameters of a transistor are dimensionless?
a) Four
b) Two
c) Three
d) One

Explanation: (i) H11 = V1/I1; for V2 = 0 (output short circuited)
This parameter is input impedance with output short.
Its unit is ohm.
(ii) H21 = i2/i1; for V2 = 0 (output short circuited)
This parameter is Current gain ratio with output short.
It is unit less or dimensionless.
(iii) H12 = V1/V2; for i1 = 0 (input open circuited)
This is voltage gain feedback ratio with terminals open.
And it is unit less or dimensionless.
(iv) H22 = i2/v2; for i1 = 0 (input open circuited)
This is output admittance with input terminals open.
Its unit is ohm-1 or mho.
Thus there are two h-parameters which are unit less or dimensionless.

10. The values of h-parameters of a transistor in CE arrangement are ________ arrangement.
a) same as for CB
b) same as for CC
c) different from that in CB
d) similar to no

Explanation: The values of h-parameter in CE arrangement:
Hie = Vbe/Ib; for Vce = 0 (output short circuited)
Hfe = ic/ib; for Vce = 0 (output short circuited)
Hre = Vbe/Vce; for ib = 0 (input open circuited)
Hoe = ic/vce; for ib = 0 (input open circuited)

The values of h-parameter in CB arrangement:
Hib = Vbe/Ie; for Vbc = 0 (output short circuited)
Hfb = ic/Ie; for Vbc = 0 (output short circuited)
Hrb = Vbe/Vbc; for ie = 0 (input open circuited)
Hob = ic/vbe; for ie = 0 (input open circuited).

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