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Published byAyanna Hume Modified over 2 years ago

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Linear Power Supply

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Outline Linear Power Supply – Poor mans 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 Rectifier Circuit

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Outline Large-Signal and Small-Signal Operation Application of Diodes (Up to 3.5.1)

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How does a small increase in V ad affect V out ?

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Drop in Output Voltage

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(Slope)

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Small Signal Resistance Small Signal Resistance: I D /V T

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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) mA mA Dynamic Resistance from the measurement: ( )/(67.57 mA mA)= Ohms

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Using Small Signal Model in a Small Signal Calculation

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Small Signal Model of Adaptor 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 Cant 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= 41.6 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

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Half-Wave Rectifier Assume constant voltage model for diodes Voltage offset Diode is off for V in < V D,on

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On for V in less than –V D,on

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Ideal Diode Model An AC-DC Converter Circuit

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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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Rectifier Driving a Resistive Load V in begins to fall after t 1 because RL provides a discharge path for C 1. C1 must be sufficient large so that the current drawn by RL does not reduce V out significantly. The diode is turned on again ripples

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C1 is called smoothing capacitor

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T in Magnitude of the Ripple (V p -V D,on )/R L is the current discharged through R L (basic form of this equation: Q=CV)

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The Maximum Forward Bias Current Maximum Forward Current Occurs at the point when the diode turns on (t 1 ) 1.C 1 dV out /dt is maximum 2.The current supplied to R L is (V p -V D,on )/R L

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Screen Shots

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Smoothed Capacitor

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