Interview Questions.

Question 1. Discuss The Need For Biasing The Transistor?

Answer :

For everyday operation, base-emitter junction ought to be forward biased and the collector-base junction opposite biased. The quantity of bias required is sizeable for the status quo of the running or the Q-point that is dictated by means of the mode of operation favored.

In case the transistor isn't always biased nicely, it might:

Work effectively
Produce distortion in the output signal
With the exchange in transistor parameters or temperature upward push, the operating point may also shift and the amplifier output may be volatile.
Question 2. What Are ‘emitter Injection Efficiency’ And ‘base Transport Factor’ And How Do They Influence The Transistor Operation?

Answer :

The ratio of modern of injected vendors at emitter junction to the full emitter cutting-edge is referred to as the emitter junction efficiency. The ratio of collector current to base present day is referred to as transport issue

i.E. β* = IC/IB

The large the cost of emitter injection performance, the larger the injected companies at emitter junction and this will increase the collector contemporary. The large the β* cost the larger the injected providers across collector junction and therefore collector cutting-edge increases.

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Question three. Which Of The Transistor Currents Is Always The Largest? Which Is Always The Smallest? Which Two Currents Are Relatively Close In Magnitude?

Answer :

The emitter present day IE is usually the most important one. The base contemporary IB is continually the smallest. The collector cutting-edge IC and emitter present day IE are exceedingly near in importance.

Question four. Why Silicon Type Transistors Are More Often Used Than Germanium Type?

Answer :

Because silicon transistor has smaller cut-off current ICBO, small versions in ICBO because of versions in temperature and excessive running temperature as compared to those in case of germanium type.

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Question five. Why Collector Is Made Larger Than Emitter And Base?

Answer :

Collector is made physically larger than emitter and base due to the fact collector is to use up plenty energy.

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Question 6. Why The Width Of The Base Region Of A Transistor Is Kept Very Small Compared To Other Regions?

Answer :

Base vicinity of a transistor is stored very small and really gently doped as a way to skip maximum of the injected fee providers to the collector.

Question 7. Why Emitter Is Always Forward Biased?

Answer :

Emitter is constantly forward biased w.R.T base with the intention to supply majority rate providers to the base.

Question eight. Why Collector Is Always Reverse-biased W.R.T Base?

Answer :

Collector is constantly opposite-biased w.R.T baseso as to get rid of the fee providers from the base-collector junction.

Question nine. Can A Transistor Be Obtained By Connecting Tow Semiconductor Diodes Back-to-returned?

Answer :

No. Because in case of  discrete back-to-returned related diodes there are 4 doped areas in preference to three and there may be not anything that resembles a skinny base vicinity between an emitter and a collector.

Question 10. Define Beta Of A Transistor?

Answer :

The β factor transistor is the not unusual emitter modern gain of that transistor and is defined as the ratio of collector contemporary to the bottom modern:

Β = IC/IB

Question 11. Why Is There A Maximum Limit Of Collector Supply Voltage For A Transistor?

Answer :

Although collector current is practically unbiased of collector deliver voltage over the transistor operating range, however if VCB is growth beyond a certain vale collector contemporary IC is subsequently increases hastily and likely destroys the device.

Question 12. Explain Why Iceo >> Icbo?

Answer :

The collector reduce-off modern-day denoted by way of ICBO is a whole lot larger than ICBO. ICEO is given as:

ICEO = ICBO/ (1-α)

Because α is nearly identical to harmony (slightly much less than unity), ICEO >> ICBO

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Question thirteen. Why Ce Configuration Is Most Popular In Amplifier Circuits?

Answer :

CE configuration is specifically used because its contemporary, voltage and power profits are pretty high and the ratio of output impedance and input impedance are pretty moderate.

Question 14. Why Cc Configuration Is Called A Voltage Buffer? What Is Other Name?

Answer :

Because of its excessive enter impedance and low output impedance, the common collector circuit reveals wide software as a buffer amplifier among a high impedance source and low impedance load. It is referred to as a voltage buffer. Its other name is emitter follower.

Question 15. What Are The Main Purposes For Which A Cc Amplifier May Be Used?

Answer :

Because of its excessive enter impedance and occasional output impedance, the commonplace collector circuit reveals extensive software as a buffer amplifier between a high impedance source and coffee impedance load.

Question 16. Which Configuration Among Ce, Cb, And Cc Gives Highest Input Impedance And No Voltage Gain?

Answer :

Common collector configuration has the best input impedance and has voltage advantage much less than team spirit.

Question 17. What Do You Understand By Collector Reverse Saturation? In Which Configuration Does It Have A Greater Value?

Answer :

When enter modern (IE in case of CB configuration and IB in case of CE configuration) is zero, collector present day IC isn't always 0 although it may be very small. In truth that is the opposite leakage present day or collector reverse saturation contemporary (ICBO or certainly ICO in CB configuration and ICEO in CE configuration). In case of CE configuration it's miles plenty extra than that during case of CB configuration.

Question 18. What Is Meant By Operating Point?

Answer :

Quiescent point is a factor at the dc load line which represents VCE and IC in the absence of ac signal and versions in VCE and IC take place round this factor while ac signal is carried out.

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Question 19. Explain How Bjt Can Be Used As An Amplifier?

Answer :

A transistor operates as an amplifier by way of switch of the contemporary from low impedance loop to high impedance loop.

Question 20. What Kinds Of Bipolar Transistors (bjts) Exist?

Answer :

There are two styles of bipolar transistors:  NPN type and PNP kind. The NPN-kind lineup stages from excessive- to low-voltage products, and the PNP-kind lineup consists of merchandise underneath 400 V. (Products under 2 hundred V are broadly available.)

Question 21. What Is The Function Of Bjts?

Answer :

They exchange small indicators to massive signals. This is known as amplification. The ratio of collector modern-day IC and base cutting-edge IB (IC/IB) is called DC modern benefit, denoted as hFE.

Question 22. What Is The Relation Between Base-emitter Current And Collector-emitter Current In A Bipolar Transistor?

Answer :

When small current (IB) flows from base to emitter, modern of IB x hFE flows from collector to emitter in NPN transistor.

Question 23. Technical Documents For Individual Power Transistors Contain A Safe Operating Area (soa) Graph. What Is It?

Answer :

The secure running area (SOA) is very vital for the operation of a power transistor because the SOA graph specifies the voltage and modern-day situations in which a strength transistor can be used appropriately. The borders of the secure running region are widely defined via a thermal dissipation restrict and the restriction given with the aid of secondary breakdown.

Question 24. What Is The Difference Between Small-signal Transistors And Power Transistors?

Answer :

There is not any internationally uniform type distinguishing between small-sign and electricity transistors. Toshiba refers to transistors with energy dissipation (PC) of one W or much less as "small-sign transistors," and people with a PC better than 1 W as "electricity transistors."

Question 25. How Can I Calculate The Junction-to-ambient Thermal Resistance, Rth (j-a), Of A Small-sign Transistor?

Answer :

The junction-to-ambient thermal resistance, Rth (j-a), of a small-sign transistor may be calculated from its collector energy dissipation as follows:

Equation: Rth (j-a) ? (Tj Max - Ta? / PC MAX
Rth (j-a): Junction-to-ambient thermal resistance.
Tj Max: Maximum junction temperature.
Ta: Ambient temperature (temperature circumstance of PC Max).
PC Max: Maximum collector electricity dissipation.
Question 26. What Kinds Of Transistors Exist?

Answer :

Transistors are classified into three kinds: bipolar (BJTs), subject impact (FETs) and insulated-gate bipolar (IGBTs).

Question 27. Are Transistors Driven By Current Or Voltage?

Answer :

Bipolar transistors are modern-day-pushed devices, and field-impact transistors (FETs) and insulated-gate bipolar transistors (IGBTs) are voltage-driven devices.

Question 28. Is It Ok To Use A Transistor As A Diode?

Answer :

Bipolar transistors are not meant for use as diodes. Use diodes in case you want the diode capability. A bipolar transistor is modeled as equal to 2 diodes connected lower back-to-back with a not unusual anode or cathode terminal. The common terminal, which serves as the base terminal of a bipolar transistor, is fabricated the use of a great pattern technique with a purpose to achieve electrical characteristics necessary for a transistor; its shape is absolutely extraordinary from that of a diode.

Question 29. Are There Any Reasons Why Junction-to-case (or Channel-to-case) Thermal Resistance Is Not Specified For Small-bundle Devices?

Answer :

Neither junction-to-case thermal resistance, Rth (j-c), nor channel-to-case thermal resistance, Rth (ch-c), is specified because small-package deal gadgets do now not deplete much heat and because temperatures at the floor of small applications can't be measured accurately. For thermal design, use both junction-to-ambient thermal resistance, Rth (j-a), or channel-to-ambient thermal resistance, Rth (ch-a), instead.