Basic Electronics Notes — B.Tech ECE Sem 1

Basic Electronics — Introduction

Electronics — electrons ke controlled flow ka study jo devices aur systems mein useful work kare.

Passive vs Active Components: | Type | Components | Define | |------|-----------|--------| | Passive | R, L, C | Energy store/dissipate, no amplification | | Active | Diode, BJT, FET, Op-Amp | Amplification possible, need power supply |

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1. Semiconductor Physics

Intrinsic Semiconductor:

• Pure Silicon/Germanium
• 4 valence electrons — covalent bonds
• At 0K: no free electrons (insulator)
• At room temp: thermal energy breaks bonds → electron-hole pairs

Extrinsic (Doped) Semiconductor:

N-type: Add Phosphorus/Arsenic (5 valence electrons)
  → Extra electron = majority carrier
  → Holes = minority carrier
  → No net charge (neutral material)

P-type: Add Boron/Aluminum (3 valence electrons)
  → Hole = majority carrier
  → Electrons = minority carrier
  → No net charge (neutral material)

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2. P-N Junction Diode

Formation: P-type and N-type crystal ko join karo → electrons diffuse to P, holes to N → Depletion Region banti hai (no free carriers) → built-in electric field.

Biasing:

Forward Bias (P→+ V→-):
  External voltage overcomes built-in potential (~0.7V Si, 0.3V Ge)
  Current flows (mA range)
  I = I₀(e^(V/ηVT) - 1)  [Shockley equation]

Reverse Bias (P→- V→+):
  Depletion widens → current blocked
  Only small reverse saturation current I₀ (nA range)
  At breakdown voltage → large current (avalanche/zener)

Diode VI Characteristics:

     I (mA)
     │  Forward bias
  20 ┤       /
  10 ┤     /
     ├───/──────────── V
    Vf      Reverse bias
(0.7V Si)
     │ -I₀ (nA)

Diode Applications:

• Rectification (AC → DC)
• Clipping circuits
• Clamping circuits
• Voltage multipliers
• Logic gates (diode logic)

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3. Rectifier Circuits

Half-Wave Rectifier

AC ─┬──[D1]──┬── +VDC
    │         │
    └─────────┴── GND

Output: only positive half cycles
Vrms = Vm/2 = 0.5Vm
Vdc = Vm/π = 0.318Vm
Ripple factor = 1.21
Efficiency = 40.6%
Peak Inverse Voltage (PIV) = Vm

Full-Wave Bridge Rectifier

      D1      D3
  +──►|──┬──►|──+
AC |    │    │   DC output
  -──►|──┘──►|──-
      D2      D4

Both half cycles utilized
Vdc = 2Vm/π = 0.636Vm
Efficiency = 81.2%
PIV = Vm
Ripple frequency = 2f

Filter Circuits

Capacitor filter after rectifier:
Ripple voltage Vr = Idc/(f×C)
Ripple factor ≈ 1/(2√3 × f × R × C)

Larger C → smoother DC, less ripple

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4. Special Diodes

Zener Diode (Voltage Regulator)

Operates in reverse breakdown region
Maintains constant Vz (zener voltage)

Voltage Regulator Circuit:
Vin ──[Rs]──┬── Vout
             │
           [Zener]
             │
            GND

Rs = (Vin - Vz) / (IZ + IL)
Minimum IZ ≈ 5mA (keep in regulation)

| Zener Voltage | Application | |--------------|-------------| | 2.4-3.3V | Logic circuits | | 5.1V | TTL reference | | 12V | Power supply ref | | Custom | ADC/DAC reference |

LED (Light Emitting Diode)

• Forward biased P-N junction → photons emitted
• Recombination energy → light (instead of heat in Si)
• GaAs, GaP, InGaAsP materials
• Color depends on bandgap
• Forward voltage: Red 1.8V, Green 2.1V, Blue 3.3V

Photodiode

• Reverse biased → light generates electron-hole pairs
• Photocurrent proportional to light intensity
• Used in optical communication, sensors, solar cells

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5. Bipolar Junction Transistor (BJT)

Structure:

NPN: N-Emitter | P-Base | N-Collector
PNP: P-Emitter | N-Base | P-Collector

Terminals: Emitter (E), Base (B), Collector (C)
Active region: BE forward, BC reverse biased

Current Relations:

IE = IB + IC
IC = β × IB  (β = hFE = current gain, 20-500)
IC = α × IE  (α = 0.95-0.999)
α = β/(β+1)

Small base current controls large collector current!

Configurations: | Config | Input | Output | Current Gain | |--------|-------|--------|-------------| | CE (Common Emitter) | B | C | High (β) | | CB (Common Base) | E | C | <1 | | CC (Common Collector) | B | E | High (β+1) |

Load Line Analysis:

VCC = IC × RC + VCE
IC = (VCC - VCE) / RC

Q-point (Operating Point) on load line:
Cutoff: IC≈0, VCE≈VCC
Saturation: IC≈VCC/RC, VCE≈0.2V
Active: between — for amplification

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6. JFET & MOSFET Introduction

JFET:

• Gate voltage controls channel width → drain current
• N-channel: electrons, P-channel: holes
• VGS = 0 → maximum ID (IDSS)
• VGS negative → pinch off

MOSFET (most important):

Enhancement MOSFET (NMOS):
VGS > Vth → channel forms → current flows
VGS < Vth → no channel → off

Depletion MOSFET:
Channel exists → VGS = 0 → current flows
VGS negative → channel depleted → off

MOSFET dominates IC design — billions per chip, low power.

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Exam Important Questions

1. P-N junction diode ki VI characteristics draw karo
2. Full-wave bridge rectifier ka circuit aur working
3. Zener diode voltage regulator circuit design karo (Vin=12V, Vout=5V, IL=50mA)
4. BJT ke teen configurations compare karo
5. Forward bias aur reverse bias mein kya fark hai?
6. LED aur normal diode mein kya difference hai?
7. JFET aur MOSFET mein kya fark hai?
8. Filter circuit kyun use karte hain rectifier ke baad?

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Viva Questions

Q: Silicon ko Germanium se zyada prefer kyun karte hain? A: Si ka bandgap zyada (1.12eV vs 0.67eV) → less leakage current at room temp. Si naturally SiO₂ banata hai (excellent insulator for MOS). Si earth mein abundant. Higher operating temperature.

Q: Transistor as switch aur amplifier mein kya fark hai? A: Switch: cutoff (off) ya saturation (on) region mein operate karta hai. Amplifier: active/linear region mein operate — small signal change → large output change.

Q: PN junction mein built-in voltage (barrier potential) kyun hota hai? A: Diffusion se electrons P-side mein aur holes N-side mein chale jaate hain → ions exposed hote hain → electric field banta hai jo diffusion oppose karta hai → equilibrium mein ~0.7V Si.