What is a BJT?

2 Answers

BJT is a bipolar junction transistor. BJT have three terminal. Base, emitter and collector are the three terminals of BJT. BJT is a current controlled device. NPN and PNP are the two types of BJT.
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Bipolar Junction Transistor (BJT):

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BJT is a Bipolar device. (Uses both electrons and holes charge carrier for current conduction)
Two Junctions (Emitter junction & collector junction)
Transfer-Resistor (Transistor) (Amplify by transferring signal from lower resistance to higher resistance region)
BJT is minority carrier device.
Three terminal device
Emitter (More doped) (Smaller area)
Base (Thin & lightly doped)
Collector (Less doped)(Larger area)
Two type semiconductor
N-type and P-type
N-type (Electrons are carrier)
P-type (Holes are carrier)
NPN and PNP
Basic function is to amplify current
Use as amplifiers and switches
BJT is a current controlled device.
The input impedance of BJT is low.
Small base current.
Emitter (Emits electrons)
Collector (Collects electrons)
Current gain β = Ic/Ib
The drive circuit of BJT is complex.
Switching speed of BJT is in the range of microseconds means slow switching speed.
BJT is the negative temperature coefficient device.
Conduction losses are low.
Switching losses are high for high frequency.
Applications: computer, mobile phones, audio amplifiers, radio etc.
Active mode (Current amplification)
Cutoff mode (Open switch)
Saturation mode (Close switch)
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Related questions

Answer : Active , Saturation , Cut-off region of operations in BJT.

Answer : The proper flow of zero signal collector current and the maintenance of the proper collector emmiter voltage during passage of single called as transistor biasing

Answer : Beta is the current gain which is the ratio of collector current to base current.

Answer : Bipolar junction transistor

Answer : Transformer coupled amplifiers Direct coupled amplifiers Multistage amplifiers Darlington amplifiers Emmiter follower

Answer : Bjt transistor is a type of transistor which  uses both electrons and hole charge carrier.bjts are used as switches and amplifiers.They amplify currents.

Description : An FET is a better chopper than a BJT because it has (A) lower offset voltage (B) higher series ON resistance (C) lower input current (D) higher input impedance

Answer : An FET is a better chopper than a BJT because it has lower offset voltage

Answer : Yes IGBT is costlier than BJT and MOSFET.

Answer : Yes BJT have internal capacitances.

Answer : BJT act as switch in saturation and  cutoff region ( ON state in saturation region and OFF state in cut-off region )

Answer : In cut-off region of BJT both the emitter-base junction and collector-base junction are reverse biased.

Answer : Active region of BJT act as amplifier.

Answer : Yes BJT have second breakdown problem.

Answer : BJT is current controlled device.

Answer : BJT have three terminals Base, emitter and collector.

Answer : In  BJT  there  is  movement  of   electrons  and  holes   accros  the  junctions  which  is  basicaly  current  flow.

Answer : When Q-point is at cut off region means it is just above the horizontal axis VCE

Answer : BJT control the flow of electron so it is a active device.

Answer : No, BJT is a current controlled device .

Description : What is the difference between BJT and FET?

Answer : BJT  is  a  current  opperated   transistor  while  FET   is  a  field   opperated  transistor.

Description : What is a BJT amplifier?

Description : What is the difference between beta and forced beta for BJT?

Description : What is the value of Beta in power BJT?

Answer : The beta value in power BJT is 5 to 10.

Description : State 2 advantages of JFET over BJT.

Answer : Advantages of JFET over BJT: 1) High input impedance 2) Better thermal stability 3) Produce less noise 4) Smaller than BJT 5) Rugged in construction and simpler to fabricate 6) High degree of isolation between Input and Output. 

Description : List specification of BJT.

Answer : * The bipolar junction transistor (BJT) has small signal current gain, α (hfb). * Maximum collector current Ic (max). * Maximum collector to emitter voltage, VCE (max). * Collector to emitter ... . * Collector to emitter cut off voltage, VCEO. * Base emitter saturation voltage, VBE (sat).

Description : State reason BJT is called as bipolar junction transistor.

Answer : BJT is called bipolar junction transistor because in BJT current conduction takes place due to majority as well as minority charge carriers.

Description : List configurations of BJT. 

Answer : Configurations of BJT : 1) Common Base (CB) configuration 2) Common Emitter (CE) configuration 3) Common Collector (CC) configuration

Description : State the need of biasing of BJT.

Answer : Need of biasing: The basic need of transistor biasing is to keep the base-emitter (B-E) junction properly forward biased and the collector-emitter (C-E) junction properly reverse biased ... transistor biasing is necessary for normal and proper operation of transistor to be used for amplification. 

Description : Draw circuit diagram of voltage divider biasing list two advantages of voltage divider biasing of BJT.

Answer : Two advantages of voltage divider biasing of BJT. 1. It is very simple method of transistor biasing. 2. The biasing conditions can be very easily set. 3. there is no loading of ... 5. The resistor RE introduces a negative feedback. So all the advantages of negative feedback are obtained. 

Description : Compare BJT with FET

Answer : FET BJT It is unipolar device i.e. current in the device is carried either by electrons or holes It is bipolar device i.e. current in the device is carried either by ... from minority- carrier storage effects & therefore has lower switching speeds & cut-off frequencies. 

Description : Compare between BJT and FET on the basis of (i) Biolar/Unipolar (ii) Tharmal Runaway (iii) Noise (iv) Applications

Answer : Parameter BJT FET Bipolar/Unipolar It is bipolar device i.e. current in this device is carried by electrons and holes. It is unipolar device i.e. current ... in oscilloscopes, electronic voltmeters and other measuring and testing equipment because of their high input impedance.

Description :  If the base current of a BJT is 250 µA and emitter current is 15 mA, then the common base current gain will be A) 0.98 B) 0.41 C) 59 D) 55  

Answer :  If the base current of a BJT is 250 µA and emitter current is 15 mA, then the common base current gain will be 0.98 

Description : Which phenomenon is present in thyristors but absent in BJT, MOSFET and IGBT ? (A) forward conduction (B) latching (C) forward blocking (D) reverse breakdown

Answer : Which phenomenon is present in thyristors but absent in BJT, MOSFET and IGBT ? (A) forward conduction (B) latching (C) forward blocking (D) reverse breakdown

Description : How can BJT be used as an amplifier?

Description : Is the input impedance of MOSFET more than BJT and FET?

Answer : Yes, the input impedance of MOSFET more than BJT and FET.

Description : Explain open emitter BJT drive circuit.

Answer : open emitter BJT drive circuit:

Description : Explain the formation of parasitic BJT and parasitic diode in Power MOSFET. Can parasitic diode be used in same power electronics applications?

Answer : Parasitic Diode: The parasitic diode is in between drain and source. The MOSFET structure itself contains parasitic diode or body drain diode. This parasitic diode allows the reverse flow of current when the ... of MOSFET as a BJT collector. Parasitic BJT operates in the cut-off region.

Description : Operating frequency of power MOSFET is higher than that of power BJT. Justify the statement.

Answer : Power MOSFET have high turning on and turning off capability high switching speed of MOSFET is due to the high rate of change of drain voltage. The switching losses of power MOSFET ... lower frequency. Hence, operating frequency of power MOSFET is higher than that of power BJT.

Description : Compare BJT, MOSFET and IGBT .

Answer : BJT MOSFET IGBT BJT is a current controlled device. MOSFET is a voltage controlled device. IGBT is a voltage controlled device. The input impedance of BJT is low. ... is minority carrier device. MOSFET is majority carrier device. IGBT is minority carrier device.

Description : Explain the on state losses in power BJT.

Answer : On state losses in power BJT: Transistor have four types of losses one is turn on state losses second is turn off state losses third is turn on switching losses and fourth is turn ... ON = VCE sat x IC With increasing collector current collector to emitter saturation voltage increases.

Answer : Because it has a higher switching frequency and heat tolerance.

Answer : ON state losses of IGBT is less as compared to MOSFET and BJT.

Description : FET is advantageous in comparison with BJT because of  A) High input impedance B) High noise C) High gain bandwidth product D) Its current controlled behavior

Description : Compared to MOSFET operational amplifier, BJT operational amplifier has  A) Higher input resistance B) Higher slew rate C) Lower input current D) Higher voltage gain

Description : Is BJT unipolar or bipolar Why?

Answer : Bipolar Junction Transistor (BJT) is a bipolar device because current is carried by both holes and electrons hence it is called bipolar.

Description : Why BJT is a current control device?

Answer : BJT have three terminal emitter, base and collector. The collector current is the output current. The collector current (Ic) is controlled by base current hence BJT is called current controlled device.

Description : What is an emitter follower BJT circuit ? (A) Common Collector Amplifier (B) Common Emitter Amplifier (C) Common Base Amplifier (D) None of the above

Answer : What is an emitter follower BJT circuit ? (A) Common Collector Amplifier (B) Common Emitter Amplifier (C) Common Base Amplifier (D) None of the above

Description : What are the main constructional differences between a MOSFET and a BJT? What effect do they have on the current conduction mechanism of a MOSFET? 

Answer : A MOSFET like a BJT has alternating layers of p and n type semiconductors. However, unlike BJT the p type body region of a MOSFET does not have an external electrical connection. The gate ... .  Distributed under Creative Commons Attribution-ShareAlike - CC BY-SA. Version 2 EE IIT, Kharagpur

Answer : Q pointit is nothing but operating point of transistor which can gives the information about the transistor working in active cutoff or saturation region to the Faithful amplification we have to ... of proper collector emitter voltage during the passage of signal is known as transistor biasing

Description : Draw the output characteristics of BJT in CE configuration and label various regions on it.

Answer :  output characteristics of BJT in CE configuration 

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