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Linear Power Supply

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**Outline Linear Power Supply Adjustable power supply Rectifier Circuit**

Poor man’s cell phone charger Small signal resistance Adjustable power supply Rectifier Circuit Half-wave rectifier circuit Full-wave rectifier circuit Full-wave rectifier circuit as a Frequency mixer Filter Circuit

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**Outline Large-Signal and Small-Signal Operation**

Application of Diodes (Up to 3.5.1)

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c03f19 How does a small increase in Vad affect Vout?

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Drop in Output Voltage

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c03f20 (Slope)

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**Small Signal Resistance**

Small Signal Resistance: ID/VT

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**I-V Characteristic of a 1n4001 Diode**

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**Export I-V Data to a Table**

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Export Table

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**Small Signal Resistance**

VF (V) IF (Computed) 0.748 67.57 mA 0.740 57.89 mA Dynamic Resistance from the measurement: ( )/(67.57 mA mA)= Ohms ( )/(13.8 mA-5.74 mA)= 48 mV/8.06 mA =5.95 Ohms

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c03f22 Using Small Signal Model in a Small Signal Calculation

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c03f23

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**Small Signal Model of Adaptor**

c03f25 Change in Vad

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**How should a load be modeled?**

A laptop consumes an average power of 25 W with a supply voltage of 3.3 V. Determine the average current drawn from the batteries or the adaptor. P=VI I= 7.56 A If the laptop is modeled by a resistor, then RL is Ohms.

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**You Can’t Power a Laptop with a Circuit Like this!**

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**How should a Cellphone load be modeled?**

A cellphone consumes an average power of 100 mW with a supply voltage of 2.4 V. Determine the average current drawn from the batteries or the adaptor. P=VI I= mA If the cellphone is modeled by a resistor, then RL is 79 Ohms.

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**Use a 79 Ohm Resistor to Model a Cell Phone Load**

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**Dual-Output Adjustable Linear Regulated Power Supply**

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Block Diagram

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Simple Description Transformer: “Downconvert” the AC line voltage to a smaller peak voltage Vm, usually about 2-3 Volts larger than the ultimately desired DC output. Diode Rectifier Circuit: produce a waveform with large DC component. Filter: smooth out the rectified sinusoid. Regulator: eliminate residual ripple

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c03f27 c03f27

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**c03f28 Half-Wave Rectifier Assume constant voltage model for diodes**

Voltage offset Diode is off for Vin < VD,on Assume constant voltage model for diodes

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c03f29 On for Vin less than –VD,on

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c03f31 An AC-DC Converter Circuit Ideal Diode Model

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**c03f30 An AC-DC Converter Circuit**

Constant Voltage Diode Model Issue: It remains to be seen whether it can provide a current to a load

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**How should a load be modeled?**

A laptop consumes an average power of 25 W with a supply voltage of 3.3 V. Determine the average current drawn from the batteries or the adaptor. P=VI I= 7.56 A If the laptop is modeled by a resistor, then RL is Ohms.

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**c03f32 Rectifier Driving a Resistive Load The diode is turned on again**

ripples Vin begins to fall after t1 because RL provides a discharge path for C1. C1 must be sufficient large so that the current drawn by RL does not reduce Vout significantly.

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c03f33 C1 is called smoothing capacitor

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**c03f34 Magnitude of the Ripple Tin (Vp-VD,on)/RL is the current**

discharged through RL (basic form of this equation: Q=CV)

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**c03f35 The Maximum Forward Bias Current**

Maximum Forward Current Occurs at the point when the diode turns on (t1) C1dVout/dt is maximum The current supplied to RL is (Vp-VD,on)/RL

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Screen Shots

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Smoothed Capacitor

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EE 348: Lecture Supplement Notes SN2 Semiconductor Diodes: Concepts, Models, & Circuits 22 January 2001.

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