Applications of Diodes Study Notes

Diode Rectification

• Rectification is the process of converting alternating current ($AC$) into pulsating direct current ($DC$).

• Half-Wave Rectifier:

  • Uses a single diode that conducts during the positive half-cycle (forward biased) and blocks current during the negative half-cycle (reverse biased).
  • Consists of three primary components: transformer, diode, and resistive load.
  • Exhibits high ripple content and low rectification efficiency.
  • 

• Full-Wave Rectifier:

  • Converts both halves of the $AC$ input cycle into a continuous pulsating $DC$ output.
  • Utilizes either a two-diode center-tapped transformer configuration or a four-diode bridge rectifier configuration.
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• Full-Wave Rectifier Performance Characteristics:

  • Ripple Factor: $\gamma = \sqrt{\left(\frac{V_{rms}}{V_{DC}}\right)^2 - 1}$
  • $DC$ Load Current: $I_{DC} = \frac{2 I_{max}}{\pi}$
  • $DC$ Output Voltage: $V_{DC} = \frac{2 V_{max}}{\pi}$
  • Form Factor: $1.11$
  • Rectifier Efficiency: $81.2\%$

Voltage Regulation

• Voltage regulation is the ability of a power system or regulating circuit to maintain a constant output voltage level despite variations in input line voltage or load conditions.

• Alternator Voltage Regulation Formula:

  • $\text{VR} = \frac{|V_{nl} - V_{fl}|}{|V_{fl}|} \times 100\%$
  • Where $V_{nl}$ is the no-load terminal voltage and $V_{fl}$ is the full-load terminal voltage.

• Primary Regulation Types:

  • Line Regulation: Maintains constant output voltage as input supply voltage fluctuates.
  • Load Regulation: Maintains constant output voltage as load current demand changes.
  • Series Regulation: The regulating element is connected in series with the load to adjust resistance dynamically.
  • Shunt Regulation: The regulating element is connected in parallel with the load to divert excess current.

Light Emission (LED)

• A Light-Emitting Diode (LED) is a heavily doped p-n junction semiconductor device that emits photons via electron-hole recombination when forward biased.

• 

• Wavelength & Color Composition:

  • Aluminium gallium indium phosphide alloys: Used to produce red, orange, and yellow light emissions.
  • Indium gallium nitride alloys: Used to produce green, blue, and white light emissions.

• Forward Current Formula:

  • $I_F = \frac{V_s - V_D}{R_s}$
  • Where $I_F$ is forward current, $V_s$ is source voltage, $V_D$ is LED forward voltage drop, and $R_s$ is the current-limiting resistor.

Signal Demodulation

• Demodulation is the process of recovering the original baseband message or audio signal from a modulated high-frequency carrier wave at the receiver side.

• Demodulation Circuit Techniques:

  • Diode Rectifier Envelope Detector: Converts amplitude-modulated ($AM$) signals using a single diode and a capacitor to smooth out radio frequency ($RF$) ripples.
  • 
  • Product Detector: Demodulates single sideband ($SSB$) signals using a local crystal oscillator and low-pass filter.
  • Synchronous / Coherent Detection: Multiplies the incoming signal with a synchronized local oscillator signal to retrieve baseband data.
  • FM Demodulation: Uses Frequency Discriminators or Phase-Locked Loops ($PLL$) combined with a Voltage-Controlled Oscillator ($VCO$).
  • PM Demodulation: Converts phase-modulated signals into $AM$ signals via homodyne detection prior to amplitude demodulation.

• Applications: Key to radio broadcasting, radar systems, television signal reception, underwater acoustic communication, and medical imaging ($MRI$ and ultrasound).