Basic Electronics

Fundamentals of semiconductor devices and their practical applications.

🔧 P-N Junction Diode

A semiconductor device with P-type and N-type materials joined together.
Forward Bias: Allows current to flow (low resistance).
Reverse Bias: Blocks current (high resistance).
Applications: Rectification (AC to DC), voltage clamping, signal demodulation.

🔧 Transistors (NPN & PNP)

Three-layer semiconductor devices with terminals: Emitter, Base, and Collector.
NPN: Current flows from collector to emitter when base is positive.
PNP: Current flows when base is negative w.r.t emitter.
Applications: Switching, Amplification.

🔧 Bipolar Junction Transistor (BJT)

Current-controlled device where a small base current controls a larger collector current.
Modes of operation: Cut-off, Active, and Saturation.
Use: Amplifier, digital switch, oscillator circuits.

🔧 Junction Field Effect Transistor (JFET)

Voltage-controlled device; current flows from drain to source, controlled by gate voltage.
Types: N-channel and P-channel JFET.
High input impedance: Doesn’t load input signal.
Applications: Buffer amplifiers, voltage-controlled resistors.

🔌 Simple Circuits Using Electronic Devices

Rectifier: Uses diodes to convert AC to DC.
Amplifier: BJT/JFET used to increase signal strength.
Switch: NPN transistor used as ON/OFF control in digital logic.
LED Driver: Diode + resistor + NPN transistor for light control.

📘 Previous Year Questions

Q: What happens when a PN junction is reverse biased?
Ans: It blocks current flow.
Q: Which terminal controls a BJT?
Ans: Base terminal.
Q: Which transistor is a voltage-controlled device?
Ans: JFET.