Flash Tubes in SingleUse Cameras

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Flash Tubes in Single-Use Cameras

• ENGR 120
• Fall 2001

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Flash Tube Operation

• Sealed tube filled with low-pressure xenon gas
• Under correct conditions, electrical current will
  flow through electrodes causing bright white
  flash
• Typically use very high voltages

3
Workable Circuit
Flash Tube
350 V Supply
Switch
4
But Not Practical!

• Batteries generate low voltage (234 1.5 volt
  batteries in series!)
• High voltage switch requires special design,
  protection
• Reliability, weight, cost constraints all come
  into play

5
Address the Problem

• Low voltage, low current and slow power source
  (AA cell)
• High voltage, fast acting load
• Time available between flashes
• All this indicates a need to raise the voltage
  and store the power
• Transformers
• Capacitors

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Transformers

• Change voltage level
• Operate only on AC (or varying current flow)
• Can change voltage by factors of 100 or more
• Highly reliable, inexpensive

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Capacitors

• Store charge
• Can be charged up over long period, discharged
  very quickly
• Energy storage is easily computed

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Solution 2 Circuits

• Use a transformer along with a switching
  transistor to create a high voltage to charge the
  capacitor (what makes the sound?)
• Use a switch on the shutter to discharge the
  capacitor onto the flash tube

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Typical Circuit
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Measurements from the bench

• Capacitor Voltage at full charge 350 Volts
• Capacitor Voltage after flash 60 Volts
• Compute Energy Used in each flash
• C 160 mf (micro farads)

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Using PowerPoints Drawing Tools
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Using Power Point 3-D Settings
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Build Complex Shapes