Download Power Source for Embedded Systems

Power Source for Embedded
Systems
Kyung Kim
11/28/2004
Outline
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Introduction
Wireless power transmission
Solar panel
Embedded system approach of charge
controller for backup battery
• Summary
Introduction
• Embedded systems get smaller.
• Everything is wireless these days.
• Many embedded systems are required to run
in places where power grid cannot reach for
long period of time.
Wireless power transmission
Tesla’s wireless power
• The idea became possible
in 1940 when Nicola Tesla
got his patent for wireless
radio and Dr. William
Brown developed dipole
rectifier with 90% eff. of
converting microwave
beam to DC electricity.
Wireless power using microwave
• High power microwave beam is used to transmit
power
• 2.45 GHz is used (lower freq. interferes
communications and higher freq. may be
dangerously intense)
• Microwave beam transmission has 82% eff. due to
its own interference
• Dipole rectifier antenna has 90% receiving eff.
Wireless power using laser
• Uses infrared laser for power transmission
• Photovoltaic cells (solar panel) converts the
laser to electric power
• Photovoltaic cells only uses thin slice of sun
light spectrum wasting 80% of energy
• Infrared laser increases efficiency
Solar panel
Generating 10kW per day
Solar power density
• = o COS  (dt - wa) p
•  : solar power density on earth in kW/m2
• o: extraterrestrial power density (1.353 kW/m2)
• : zenith angle (0 when sun light is perpendicular to
ground)
• dt: direct transmittance of gases except for water
• p: the transmittance of aerosol
• wa: water vapor absorptions of radiation.
(dt=80% wa=2% p =95% at equator)
Photovoltaic cells (PV)
• PV cell is built like a diode out
of semiconductor
• Photons strike the
semiconductor material in PV
cell and break off electrons
producing DC current
Solar panels power rating
• 1.5V 100mA
• 1.5V 200mA
• 6V
50mA
Power needed to run a simple system
• PIC16F877A: 5V 4mA
• LCD(typ): 5V 4mA
• OPAMP(typ): 10V 4mA
Solar panel array
• Connect solar panels in series to increase
the voltage
• Connect solar panels in parallel to increase
the current
Simple diagram for solar panel with
embedded system
Charge controller
Embedded system approach of
charge controller for backup battery
• To power an
embedded
system, part of
the embedded
system is used
to control the
power
State
diagram
NiCd and NiMH
• NiMH: Charging
terminated at
voltage pick
• NiCd: Charging
terminated at a
point past voltage
pick
Li-Ion
• Charging terminated
when charging current
is at min 5%
• Charging terminated
when voltage reaches
to float point. (timer
may activate for topoff)
Summary
• Wireless power transmission is now an
option for power source of an embedded
system
• Solar panel with a backup battery is
effective power source for an embedded
system
• Battery charging controller can be designed
using microcontrollers and software