Lab 1 - 2B 2010

Lab 1 - 2B 2010 - ECE 2B Lab#1 Lab 1 Diode Circuits...

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1 © Bob York ECE 2B Lab #1 Lab 1 Diode Circuits Overview In this lab we will measure the I-V characteristics of diodes and learn how to establish a desired bias condition (forward conduction current) using resistor networks. We will also construct several common diode circuits such as limiters, rectifiers, and voltage doublers. Table of Contents Background information 2 Current-Voltage Characteristics and Modeling 2 Diode Types and Selection 3 Breakdown and Zener Diodes 4 Light-Emitting Diodes and Displays 5 References 6 Pre-lab Preparation 7 In-Lab Procedure 8 1.1 Diode I-V Curves and Biasing 8 Diode Forward I-V Characteristics 8 Diode Biasing Calculations 8 Diodes in Series 9 Diodes in Parallel 9 1.2 Clipping Circuits and Rectifiers 10 Clippers or Limiters 10 Zener-Based Clamp 11 Half-Wave Rectifier 11 Capacitive Smoothing 11 Full Wave Rectifier 12 1.3 Diode Voltage Multipliers 12 DC Restorer Circuit 12 Voltage Doubler 13 Cockroft-Walton Multipliers 13
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2 Diode Circuits © Bob York 2 Background information Diodes allow current to flow in one direction only, effectively an electronic “one-way street”. The inherent asymmetry of diodes requires that we distinguish between the two ends of the device. One end is called the anode (from Greek anodos meaning upward path) and the other is the cathode (from the Greek kathodos meaning “downward path”). The diode conducts when the anode is biased positively with respect to the cathode. The term diode (literally “two paths” but often taken to mean “two electrodes”) originated in the context of vacuum tubes 1 and always refers to devices that have this one-way characteristic. Semiconductor diodes often have special marks on the packages to help identify the leads, as shown in Figure 1-1. The circuit schematic symbol forms an arrow that points in the direction of current flow when the anode is biased positively with respect to the cathode as shown. Current-Voltage Characteristics and Modeling The full current voltage characteristic of a typical semiconductor diode is shown in Figure 1-2a. Above the forward threshold voltage V on the current increases rapidly. Under reverse bias only a tiny reverse saturation current flows unless the voltage exceed a critical “breakdown” value br V , at which point the reverse current increases rapidly as shown. I V Reverse saturation region Forward conduction region V on V br I V Forward conduction region V on V br Real Diode Characteristic Simple Approximation V I (a) (b) Figure 1-2 – (a) Diode I-V characteristic and (b) a simple approximation for DC circuit analyses. Note that the reverse saturation current in (a) is exaggerated for clarity, and the reverse breakdown voltage V br is usually much larger than the forward turn-on V t .
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This note was uploaded on 03/17/2010 for the course ECE 2B taught by Professor York during the Winter '07 term at UCSB.

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Lab 1 - 2B 2010 - ECE 2B Lab#1 Lab 1 Diode Circuits...

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