Junction Diode as a Rectifier 🚦

A junction diode lets current pass only when it is forward-biased, so an alternating (ac) voltage turns into a one-direction (dc) current whenever the diode conducts. This clever trick is called rectification. 😃 :contentReference[oaicite:0]{index=0}

1. Half-Wave Rectifier 🙂

  • Simple circuit: a diode in series with a load resistor RL and the secondary of a transformer.
  • During the positive half-cycle (A positive), the diode conducts → a pulse appears across RL.
  • During the negative half-cycle, the diode is reverse-biased → almost no current flows (reverse saturation current ≈ 0).
  • The peak reverse voltage across the diode must stay below its breakdown rating to keep it safe.

The output is a train of half-sinusoidal pulses in one direction—hence “half-wave.” :contentReference[oaicite:1]{index=1}

2. Full-Wave Rectifier 🚀

  • Uses two diodes and a centre-tap transformer.
  • P-sides of the diodes connect to the ends A and B of the secondary; N-sides join at a common point.
  • When A is positive (and B negative), diode D1 conducts; when B is positive, diode D2 conducts.
  • Both halves of the ac waveform now produce output pulses across RL, doubling efficiency compared to the half-wave version.
  • A bridge version with four diodes can do the same job without a centre tap.

The result: a unidirectional pulse train with twice the pulse rate of the input frequency. ⚡ :contentReference[oaicite:2]{index=2}

3. Why We Need Filters 🔍

Although the voltage is one-way, it still pulses. To get a smooth dc supply, we add a filter—usually a capacitor in parallel with RL (or an inductor in series). :contentReference[oaicite:3]{index=3}

Capacitor-Input Filter ⚡📦

  • During each peak, the capacitor charges up to the top of the pulse.
  • Between peaks it discharges slowly through the load, filling in the gaps.
  • The discharge rate depends on the time constant:

    \(\displaystyle \tau \;=\; R_L\,C\)

  • A larger \(C\) (and/or \(R_L\)) → longer \(\tau\) → smaller ripple 😊.

The output now hugs the peak value of each pulse, giving a near-steady dc voltage—perfect for power supplies! :contentReference[oaicite:4]{index=4}

4. Quick Recap of Semiconductor Basics 📝

  1. Semiconductors power almost every modern electronic gadget.
  2. Crystal structure decides whether a material behaves as a metal, insulator, or semiconductor.
  3. Resistivity ranges: metals (10-8–10-2 Ω m), insulators (>108 Ω m), semiconductors sit in between.
  4. Types: elemental (Si, Ge) and compound (GaAs, CdS, …).
  5. In an intrinsic semiconductor, electrons (\(n_e\)) equal holes (\(n_h\)).
  6. Doping turns it extrinsic: \(n\)-type (\(n_e\gg n_h\)) with donors, \(p\)-type (\(n_h\gg n_e\)) with acceptors.
  7. Charge neutrality rule: \(n_e n_h = n_i^{2}\).
  8. Electrical behaviour hinges on the energy-gap \(E_g\) between valence and conduction bands.

These fundamentals explain why diodes, rectifiers, and filters work the way they do. 🚀 :contentReference[oaicite:5]{index=5}

5. High-Yield NEET Nuggets ⭐

  • Forward vs Reverse Bias—only forward bias lets a diode conduct (key to rectification).
  • Half-Wave vs Full-Wave—full-wave doubles frequency of output pulses and boosts efficiency.
  • Centre-Tap Advantage—lets two diodes share the job; know the alternative four-diode bridge.
  • Filter Time Constant—\( \tau = R_L C \) controls ripple; bigger \(C\) → smoother dc.
  • Reverse Breakdown Safety—diode’s breakdown voltage must exceed the peak reverse ac voltage.

Master these points, and rectifier questions become a breeze! 💯