Download The first battery-powered flashlights were designed around 1899

ECE 3710 Application Notes
Name: Sean Metcalf
GTID: 902610511
Major: ME
Project Name: Linear Induction Flashlight
Source of circuit/application: http://en.wikipedia.org/wiki/Flashlight ; www. Shake-flashlights.com/ ;
hypderphysics.phy-astr.gsu.edu/hbase/electric/farlaw.htmsl
I.
Introduction of application :
The first battery-powered flashlights were designed around 1899 with the new
invention of the dry cell battery and miniaturized incandescent light bulbs. Flashlights today
use primarily incandescent light bulbs or light-emitting diodes and operate by disposable or
rechargeable batteries. In this application, a LED is used because it is more efficient than an
incandescent bulb. White LEDs produce approximately 100 lumens/watt, where as small
incandescent bulbs produce 8-10 lumens/watt. LED flashlight tends to have a longer battery
life and more robust in comparison to incandescent bulbs. Technology involved with the
design of flashlights has evolved into mechanically powered flashlights operate by electricity
generated by a form of physical work. Therefore, batteries don’t need replacement or
recharging from an electrical source. There are many ways to generate voltage for a
flashlight through mechanical work: squeezing a handle, winding a crank shaft, or shaking.
The energy stored by mechanical work can be stored in a flashlight through a spring,
flywheel, or capacitor. This application consists of a mechanically powered flashlight that
generates voltage through shaking and stores it in a capacitor.
II.
Diagram of circuit:
Figure #1) Displays diagram of circuit for linear induction flashlight with basic components
Figure #2) Displays diagram of a source
transformation. The magnet passing through
the inductor or coils of wire with velocity (V)
generates voltage, and can be symbolized as a
voltage source ( ).
Diagram of Application:
Figure #3) Displays application of the previous circuit diagram in the linear induction flashlight:
Components:
1. Magnet- permanently magnetized magnet
2. Wire Coil – copper wire coiled N times
3. Full-Wave Rectifier- consists of four diodes
4. Capacitor- used like a battery to store charge
5. LED- light source
6. Resistive load- used to pull current through LED
7. Deflector/Lens- reflects and focuses light source
8. Switch- controls currents through LED ( “ON” or “OFF”)
III.
Explanation
1. How does the circuit operate?
The flashlight basic design and operation is conceptualized through linear circuits. There’s a
voltage source generated by an electromagnet, which is essentially an inductor. The alternating voltage
source is passed through a full-wave rectifier, which consists of a diodes, resistor, and capacitor. This
converts the alternating current waveform into something that closer resembles a direct current
waveform. This is useful for storage in a battery, which is a larger capacitor in this case, that will power
the light source or light emitting diode (LED).
a.) Indicate what are the inputs and outputs
Inputs: , voltage source produced by electromagnet
Outputs:
;
b.) Relationship between the output and input (e.g. Transfer function)
c. )Explain what the circuit does and how it works.
When the flashlight is shaken, the magnet moves back and forth through the coil of wires. This
produces an electromagnetic force (EMF), and generates an alternating voltage waveform. This isn’t
particularly useful in this application, so we need a voltage and current waveform that resembles
something more direct, in order to store it. Thus, the waveform is passed through a full-wave rectifier
and stored in a capacitor, while the switch is “open”. When the switch is “closed”, the charge stored in
the capacitor discharges through the diode and resistive load. Assuming there’s enough charge stored in
the capacitor to generate a voltage greater than the forward voltage of the diode. In this particular case,
there is a light emitting diode, so light is emitted when the diode in “on”.
Figure #4) Displays voltage and loop in which the current follow, when the switch is “open”. The EMF
generates voltage, which stores charge in the capacitor or “battery”. There’s a voltage across the
capacitor associated with the voltage source.
Figure #5) Displays the circuit, when the switch is “closed”. At this point, the user has stopped shaking
the flashlight and generating voltage. Thus, the charge stored in the capacitor is discharged through the
resistive load. This pulls current through the diode and turns it “on”, emitting light.
Assuming,
, for real life diodes:
2. How the circuit interfaces with the application that you chose
The linear induction flashlight is powered mechanically through the use of an electromagnet.
The user shakes the flashlight, which contains a permanently magnetized magnet that passes through a
coil of wires many times. Faraday’s law states that a voltage is generated by changing the magnetic field.
In this case, it is generated by the magnet moving toward and away from the wire coil, which produces
an EMF. Lenz’s law states that an EMF is produced by change in a magnetic flux, and the polarity
induced by the EMF produces a magnetic field that opposes the charge that produces it.
Equation for voltage generated by a change in the magnetic field (Lenz’s Law):
 N- number of turns for the wire coil
 BA- magnetic flux
 T- rate of change in time
i.e.) Determine the change of rate in time for
(turn “on” voltage for LED), 100 turns of wire,
and magnetic flux of 5 Tesla. (Approximately the time it will take the user to shake and generate the
given voltage, under ideal conditions)
Figure #6) Displays the concept of Lenz’s Law. A magnet is move toward the coiled wired with a velocity
(V). There’s a difference in potential from the two ends of the coiled wire through a resistive load ( )
that generates a voltage. This is caused by change in the magnetic flux (BA).
IV. Conclusion
The linear induction or “shake flashlight” eliminates the problem of used or “dead” batteries
that can no longer be used to power a flashlight. Not only does this flashlight potentially save operation
costs over time, but it also contributes to a lower environmental impact. Disposal of batteries can be an
expensive process, and potentially harmful to the environment if disposed improperly. A flashlight that
doesn’t require batteries eliminates the factor of battery disposal. The components that are used in this
design of a linear induction flashlight are relatively inexpensive and readily available. This is a great
practical application of linear circuits that can be built and assembled at home.