Chapter35_PN-Circuits

# Chapter35_PN-Circuits - 3.5 Diode Applications &amp;...

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3.5 Diode Applications & Circuits 3.5.1 Temperature Sensors Diode Temperature Coefficient PTAT Sensor 3.5.2 Rectifier Circuits Half-Wave Rectifier Circuits Full-Wave Rectifier Circuits Full-Wave Bridge Rectifier Circuits 3.5.3 Voltage Regulators 3.5.4 Additional Applications Jaeger & Blalock, Chapter 3.13-3.16, page 113-128 Slides courtesy of Prof. Oliver Brand

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2 3.5.1 Temperature Sensors – Diode Temperature Coefficient – Forward-biased diode (operated with constant bias current) is frequently used for temperature sensing : Challenge: I S is proportional to n i 2 and thus (strongly) depends on temperature; as a result, the V D vs. T relationship is nonlinear Work-around: PTAT circuit using a differential setup with 2 identical diodes I D = I S e qV D /kT ! 1 " # \$ % & V D = kT q ln I D I S + 1 " # ' \$ % ( ) k T q ln I D I S (T) " # ' \$ % ( dV D dT = k q ln I D I S ! " # \$ % & ' kT q 1 I S dI S dT
3 PTAT Electronic Thermometer PTAT = proportional to absolute temperature Concept Two identical diodes biased by current sources I 1 and I 2 Resulting PTAT voltage, i.e., difference in voltage drop across the two diodes is proportional to the absolute temperature PTAT voltage circuit is heart of most of today ` s digital thermometers V PTAT = V D1 ! V D2 = kT q ln I D1 I S " # \$ % & ' ! ln I I S " # \$ % & ' ( ) * * + , - - = kT q ln I D1 I " # \$ % & ' dV PTAT dT = k q ln I D1 I " # \$ % & ' = V PTAT T Jaeger, Blalock, page 88

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4 3.5.2 Rectifier Circuits Rectifier circuit converts an ac voltage to a pulsating dc voltage ; in combination with a filter, a nearly constant dc output voltage can be generated Virtually every electronic device plugged into the wall utilizes a rectifier circuit to convert the 120-240V, 50-60Hz ac power line source to a proper dc voltage DC power supplies are a commodity and fairly inexpensive Jaeger, Blalock, page 128 Power Cube Cell Phone Charger
5 Half-Wave Rectifier with Resistive Load Sinusoidal voltage source v S = V P sin ω t is connected to a series combination of diode D 1 and resistor R Using the ideal diode model, we find that the diode is ON for v S > 0 and OFF for v S < 0, resulting in a pulsating output voltage v 0 Jaeger, Blalock, Fig. 3.42 & 3.44

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6 Half-Wave Rectifier with Resistive Load If the input voltage amplitude (e.g. V P 10 V) is not large compared to the voltage drop (0.5-1.0 V) across the forward- biased diode, the CVD model should be used for circuit analysis In many applications, a transformer is used to step-down the power line voltage to a desired level To remove time-varying
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## This note was uploaded on 10/12/2011 for the course ECE 3040 taught by Professor Hamblen during the Fall '07 term at Georgia Institute of Technology.

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Chapter35_PN-Circuits - 3.5 Diode Applications &amp;...

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