Diodes and Rectifiers

BME253L - Fall 2025

Dr. Mark Palmeri, M.D., Ph.D.

Duke University

November 12, 2025

Overview

  • Diodes: Basic operation and characteristics

  • Types of diodes: Zener, Schottky, LED, etc.

  • Rectifiers: Half-wave and full-wave

Diode Basics

Diode Overview

  • Forward Region: Positive voltage on the anode allows current flow; exponentially increases with voltage.

  • Reverse Region: Positive voltage on the cathode blocks current flow; very small leakage current.

  • Breakdown Region: Sudden increase in current at high reverse voltage (Zener breakdown).

Types of Diodes

  • Zener Diode: Used for voltage regulation; operates in reverse breakdown region.

  • Schottky Diode: Known for low forward voltage drop and fast switching speeds.

  • LED (Light Emitting Diode): Emits light when forward biased; used in displays and indicators.

  • Photodiode: Generates current when exposed to light; used in solar cells and light sensors.

Modeling Diodes as Switches

Rectifiers

Half-Wave Rectifier

Half-Wave Rectifier: Allows only one half of the AC waveform to pass; simple but inefficient.

Half-Wave Rectifier

Transformer and Rectifier Circuit

How Much Power in Half-Wave Rectified Signal?

Half-Wave Rectified Power

\[ V_{DC} = \frac{V_{peak}}{\pi} \quad , \quad P_{DC} = \frac{V_{DC}^2}{R} = \frac{V_{peak}^2}{\pi^2 R} \]

Half-Wave Rectifier with Smoothing Capacitor

Full-Wave Rectifier

  • Full-Wave Rectifier: Utilizes both halves of the AC waveform; more efficient and provides smoother output.

Full-Wave Rectifier

Full-Wave Rectifier with Transformer

Applications of Diodes

  • Voltage regulation (Zener diodes)
  • Signal demodulation
  • Power conversion (rectifiers)
  • Light emission (LEDs)
  • Photodetection (photodiodes)

Light Emitting Diodes (LEDs)

LED

Voltage Regulation with Zener Diodes

In-class demo…

Transformers

https://www.electronics-tutorials.ws/transformer/transformer-basics.html

Clipping and Clamping Circuits

Photodiode Amplifier Circuit