Economical Car Laptop Charger Group 24

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Economical Car Laptop ChargerGroup 24

• Andrew Rivera
• Joseph Holleran

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Introduction

• Our goal was to create a low cost dc-dc voltage
  converter to charge a laptop battery charger in a
  car.
• Dc-dc voltage conversion will be accomplished
  through power electronic boost conversion methods.

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Benefits

• Handiness when consumer needs to use laptop in a
  vehicle
• Provides another source with which a laptop
  battery can be charged
• Reasonable design cost
• Quality alternative to similar, high-cost
  products on the market

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Features

• High Efficiency
• Small output voltage ripple
• Stability
• Protection
• Reverse polarity
• Input voltage and current surge

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Boost Operation
http//en.wikipedia.org/wiki/Boost_converter

• DC-DC Converter
• Steps-up input voltage to attain desired output
  voltage
• Input voltage and inductor become a current
  source
• Current flowing through the diode charges the
  capacitor
• Accomplished through switching

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Boost Operation - On/Off State

• On-State
• Switch Action
• 1 On, 2 Off
• Inductor Behavior
• Charges, current ramps up
• Capacitor Behavior
• Discharges through load
• Output Voltage Reaction
• Output Voltage Decrease
• Off-State
• Switch Action
• 1 Off, 2 On
• Inductor Behavior
• Discharges, current ramps down
• Capacitor Behavior
• Charges
• Output Voltage Reaction
• Output Voltage Increases

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1
2
1
http//en.wikipedia.org/wiki/Boost_converter
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Inductor/Switching Relationship
1 Gate Drive Signal 4 Inductor Current
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MOSFET Behavior

• Switch 1
• Operation
• Conducting (On-State)
• Gate Voltage is High
• Low drain-to-source voltage
• Non-Conducting (Off-State)
• Gate Voltage is Low
• High drain-to-source voltage

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PWM control

• Controls operation of switch 1
• Uses comparator to compare output voltage to a
  reference voltage in the chip
• Output voltage scaled with voltage divider
• Low feedback voltage produces high drive signal
• High drive signal turns on switch 1
• High feedback voltage produces low drive signal
• Low drive signal turns off switch 1
• Also can be controlled with current sensing
• By scaling a voltage at the desired level to the
  current sense pin it is possible to make the PWM
  operate solely off of the voltage comparator

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Driving the MOSFET
Circuit just turned on 1-Feedback voltage 2-Drain
voltage 3-Gate output voltage
Circuit in steady state operation 1-Feedback
voltage 2-Drain voltage 3-Gate output voltage
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Tolerance Analysis

• PWM is key device for functioning of our design
• Tests run on PWM controller to enhance
  understanding of operation
• Operating frequency affects circuit losses
• Varied operating frequency and observed switching
  waveform
• Feedback voltage determines switching
• Applied under or over voltage to feedback pin
  while monitoring the output pin of the PWM

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Performance Specifications

• Ability to handle input voltages in the range of
  10 to 15 volts.
• Efficiency above 85 to limit heating any heating
  concerns in the circuit
• Voltage ripple within /- 5 to protect the
  laptop

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Initial Design Schematic
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Initial Design Considerations

• Design of the charger has two key components
• Boost conversion
• PWM design to control switching
• Choice of PWM MAX668
• Size
• SMD Pads

MAX668 .3mm between pads
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Final Design Considerations

• Same core boost design
• Different PWM choice
• Able to implement and test on breadboard
• Easy transition
• The heart of the PWM control is the same
• Poor documentation on UC3843 allowed us to use
  knowledge gained from MAX668 to optimize our
  design

UC3843 1.25mm between pins
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Final Schematic Description

• Boost components
• L1, D1, Q1,C3 and C4
• Feedback voltage divider
• R4 and R5
• Current sense
• R1 and R3
• Frequency
• C2 and R6
• Compensation
• C1 and R9

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Schematic Component Calculations
http//focus.ti.com/lit/ds/symlink/uc3843.pdf
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Testing

• Line Regulation
• Load Regulation
• Efficiency
• Ripple Voltage
• Protection

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Line Regulation Equation

• Fix output load
• Vary input voltage
• Analyze output voltage
• Ideally, line regulation 0
• Output voltage should stay constant with changes
  in input voltage

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Line Regulation Data Tables
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Line Regulation Chart
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Load Regulation Equation

• Fix input voltage
• Vary output load
• Analyze output voltage
• Ideally, load regulation 0
• Output voltage should stay constant with changes
  in output load

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Load Regulation Data Tables
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Load Regulation Chart
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Efficiency Equation

• Tested on 2 variables
• Output load
• Frequency

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Efficiency Data Table Load Variation

• Fixed Input Voltage
• 3 cases
• 10V Input
• 12V Input
• 14V Input
• Fixed Frequency
• 100kHz

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Efficiency Chart Load Variation
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Efficiency Data Tables-Frequency

• Fixed Input Voltage
• Fixed Output Load
• 3 cases
• 5Ohm
• 10Ohm
• 28Ohm

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Efficiency Chart-Frequency
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Ripple Voltage

• Output voltage ripple requirement of /- 5
• 1.5V total ripple allowed

Output Voltage Ripple, 12V Input
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Protection

• Smart component choices
• Picking parts that could handle certain voltages,
  currents, and power levels
• Reverse Polarity
• Schottky rectifier in series between input source
  and inductor
• Tested by reversing leads that connected input
  voltage (dc power supply) to our circuit
• Resulted in no functionality, but no damage

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Cost Analysis
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Successes

• Light Load Operation
• Boosting
• Line Regulation
• Minimize Output Ripple

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Short-comings

• Heavy-Load Operation
• Transient Spike Suppression
• Take past breadboard design to marketability

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Recommendations

• Low Frequency Operation to minimize loss
• Keep inductor leads short to minimize ripple
• Higher precision resistors allow for more precise
  output voltage
• Snubber to eliminate transient spikes
• Increase duty cycle to allow more operating time
  to boost the voltage

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Thank You All