# Linear Power Supply.

## Presentation on theme: "Linear Power Supply."— Presentation transcript:

Linear Power Supply

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

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

c03f19 How does a small increase in Vad affect Vout?

Drop in Output Voltage

c03f20 (Slope)

Small Signal Resistance
Small Signal Resistance: ID/VT

I-V Characteristic of a 1n4001 Diode

Export I-V Data to a Table

Export Table

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

c03f22 Using Small Signal Model in a Small Signal Calculation

c03f23

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.

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

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.

Use a 79 Ohm Resistor to Model a Cell Phone Load

Dual-Output Adjustable Linear Regulated Power Supply

Block Diagram

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

c03f27 c03f27

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

c03f29 On for Vin less than –VD,on

c03f31 An AC-DC Converter Circuit Ideal Diode Model

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

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.

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.

c03f33 C1 is called smoothing capacitor

c03f34 Magnitude of the Ripple Tin (Vp-VD,on)/RL is the current
discharged through RL (basic form of this equation: Q=CV)

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

Screen Shots

Smoothed Capacitor