MICRO FUEL CELL CONVERTER

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MICRO FUEL CELL CONVERTER

• Team 25
• Noorhafifi Jalal
• Sofia Rehan Ramli

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Micro Fuel Cell

• What is Micro Fuel Cell?
• A power source that converts chemical energy into
  electrical energy
• Uses hydrogen / methanol as fuel
• Why Micro Fuel Cell?
• Environmental-friendly
• Easier to use

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Objective

• Build a power converter that takes input from a
  micro fuel cell and delivers 3 V dc to provide a
  battery substitute for a PDA or similar device.

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Benefits and Features

• Benefits
• Good complement to micro fuel cell
• Accelerates technology advancement for mobile /
  wireless devices
• Limited battery capacity is not an issue anymore
  (micro fuel cell has relatively higher energy
  capacity compared to lithium ion battery)
• Features
• Small therefore portable
• Easy to use
• Low voltage and low power rating (not hazardous
  to user)
• Economical

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Performance Requirements

• Input voltage 0.5 - 0.7 V
• Power rating lt60 mW
• Output voltage 3 V
• Efficiency gt70 with 0.6 V input at 60 mW

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Converter Initial Design
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Gate Drive
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Changes made to Design

• 1. Startup Circuit
• Resonance due to this startup circuit is
  insufficient to power up PWM (gt 2.9 V)

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Initial Startup Output

• Maximum voltage lt 2 V

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New Startup Circuit

• Integrated into the boost converter
• Only an additional resistor is needed

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Changes made to Design

• 2. PWM Chip
• Use a different PWM chip
• Different setup

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Changes made to Design

• 3. Feedback Regulator
• Initial circuit cannot be implemented
• Requires 2 sources with the extra source to be
  set as Vref
• Our converter only receives input from micro fuel
  cell
• Alternative Shunt regulator

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Shunt Regulator

• Zener regulates the output as constant as
  possible
• Line reg ?Vout/?Vin
• Rz/(R14 Rz)
• Rz Zeners internal resistance

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Finalized Circuit
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Testing Procedures

• Startup circuit cannot be tested alone
• Voltage overshoot is instantaneous, cannot be
  observed
• Needs to be tested along with boost converter
• Therefore, PWM needs to be tested first as it
  drives the MOSFET gate in boost converter

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PWM Testing

• Tested PWM chip alone
• Vin 4V
• duty ratios are shown below

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Converter Testing

• Combined all the circuits together for testing

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Performance Requirements

• Input voltage 0.5 - 0.7 V
• Power rating lt60 mW
• Output voltage 3 V
• X Efficiency gt70 with 0.6 V input at 60 mW

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Challenges

• Efficiency
• Main defect of circuit

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Power Loss in Circuit

• Power loss across
• Diode
• MOSFET
• Shunt regulator

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Power Loss across diode

• P IdVdiode
• Id 4.95 mA
• Vdiode 0.38 V
• gt P 1.88 mW
• ? 4.21 loss
• at Pin 44.7 mW

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• Voltage difference across diode which may result
  in higher power loss

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Power Loss across Diode

• Possible solution

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Power Loss across MOSFET

• Power loss across gate drive
• Ploss QgateVsupplyfswitch
• (120nC)(4.0V)(21.930k)
• 10.53 mW
• ? lt 23.55 loss

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Power Loss across MOSFET

• Possible solution
• Choice of PWM chip
• PWM chip used is incapable of varying frequency
• PWM output supplied to the MOSFET gate is quite
  high

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Power Loss across Shunt Regulator

• Boost output voltage needs to be higher than
  Zener voltage
• There exists voltage drop between boost converter
  output and output voltage
• Ploss (Va Vb)2/R14
• (3.24-2.83)2/83.2
• 2.02 mW
• ? 4.52 loss

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Power Loss across Shunt Regulator

• Post-regulation causes significant power loss
• Possible solution feedback regulator within the
  setup of the PWM itself
• Duty ratio of PWM used is directly related to the
  boost output
• Therefore regulation within the PWM is impossible

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Example of PWM chip with external duty ratio and
frequency controller
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Conclusions

• Choice of components is important in getting
  optimum efficiency
• PWM used in circuit may help fulfilling other
  requirements, but resulting in poor efficiency
• Mounting the circuit on PCB may improve the
  efficiency
• Due to high sensitivity of the circuit