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Issue #216 July 2008
Problem 2—What is the purpose of the component marked “PTC”?
Answer 2—The component marked “PTC” is most likely a positive temperature coefficient thermistor.
If the lamp has been off, this device is cool and has a relatively low resistance, allowing a significant portion of the AC waveform generated by the oscillator to pass through the heaters at either end of the lamp tube. This helps vaporize the mercury and makes it easier to ignite the arc that will generate the light.
The current through the PTC device causes it to warm up and its resistance to increase, reducing the heater current to the tube, which helps to achieve the intended lifetime of the C
+embly.
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