Help Me I Dont Really Understand About BJT Transistor

In summary, the conversation discusses the operating principles of a sensor circuit and the use of BJT transistors as switches. The participants explain that transistors have a "saturation" mode where they act as closed switches, and the circuit in Figure (d) and (e) uses this principle to control the LED based on the resistance of the LDR. They also mention that the collector resistor limits power dissipation in the transistor. The conversation also touches on the possibility of using BJT transistors as switches and the limitations that come with it.
  • #1
NoobLala
1
0
Hyeee. This Gonna Be My First Post. Really Hope You Guys Can Help Me.

I Dont Understand On The Operating Principles Of The Sensor Circuit Shown In Figure (d) and Figure (e) . Can Someone Describe It For Me? I Have Quiz On Thisssss..Arghh.

Can BJT Transistor Works As Switch? How?

Thankksssssss :D
 

Attachments

  • Picture1.png
    Picture1.png
    12.8 KB · Views: 402
Physics news on Phys.org
  • #2
Transistors have what is called "saturation" mode, if they are off (no base current) they are like a closed switch in that no current can get from collector to emitter. If there is enough current supplied to the base then they go into saturation in which case they act like a closed switch. They are not idea switches because there is always a limit to the amount of current you can put through the collector/emitter before they melt.

That fact should make it obvious how the circuit works.
 
  • #3
Taking the 1st circuit as an example, if the LDR resistance is low (say 200 ohms) then the transistor is turned off. If the LDR resistance is high (say 1 megohm) then the transistor is on. The 100 ohm collector resistor reduces the power dissipation in the transistor by limiting Vce without appreciably affecting the LED current.

Use exactly the same approach for the second circuit.
 

Related to Help Me I Dont Really Understand About BJT Transistor

1. What is a BJT transistor?

A BJT (bipolar junction transistor) is a type of semiconductor device that is used to amplify or switch electronic signals. It consists of three layers of a semiconductor material, with two layers of one type (either P or N) sandwiching a layer of the opposite type. The layers are referred to as the emitter, base, and collector.

2. How does a BJT transistor work?

A BJT transistor works by controlling the flow of current between the collector and emitter using a smaller current at the base. When a small current is applied to the base, it allows a larger current to flow from the collector to the emitter, thus amplifying the signal. This is known as the transistor's current gain.

3. What are the differences between NPN and PNP transistors?

The main difference between NPN and PNP transistors is the direction in which the majority charge carriers (electrons or holes) flow. In an NPN transistor, the majority carriers flow from the emitter to the collector, while in a PNP transistor, the majority carriers flow from the collector to the emitter. Additionally, the direction of the base current needed to control the transistor is opposite in NPN and PNP transistors.

4. How is a BJT transistor used in circuits?

A BJT transistor is commonly used in circuits as an amplifier or switch. As an amplifier, it can be used to increase the strength of a weak signal. As a switch, it can be used to control the flow of current in a circuit by turning it on or off.

5. What are some common applications of BJT transistors?

BJT transistors have a wide range of applications in electronic devices such as computers, televisions, and cell phones. They are also commonly used in audio amplifiers, power supplies, and voltage regulators. BJT transistors are also used in digital logic circuits and as switches in electronic devices.

Similar threads

I don't understand transistors in combinations .... Or maybe basics ....
    • Electrical Engineering
2
Replies
68
Views
4K
Engineering How does BJT work in this circuit?
    • Engineering and Comp Sci Homework Help
Replies
4
Views
2K
NPN BJT transistor: base voltage / emitter current
    • Electrical Engineering
2
Replies
60
Views
13K
BJT and MOSFET complete analysis
    • Introductory Physics Homework Help
Replies
28
Views
5K
Need help in making my Electronics Project using BJT....
    • Engineering and Comp Sci Homework Help
Replies
1
Views
1K
Understanding NPN BJT Transistor: Ic & Ib Ratios
    • Electrical Engineering
Replies
4
Views
2K
BJT Switch - Circuit Simulation
    • Electrical Engineering
Replies
5
Views
3K
Engineering Analyzing the internal circuitry of IC 741 Op-Amp step by step
    • Engineering and Comp Sci Homework Help
Replies
4
Views
2K
Engineering Computing resistance in given circuit with BJT
    • Engineering and Comp Sci Homework Help
Replies
3
Views
1K
Basic Electronics: Transistor confusion
    • Electrical Engineering
Replies
2
Views
1K

Hot Threads

Recent Insights

Back
Top