Yes, neon bulbs generally need a resistor in series to limit the current and prevent damage.
Neon bulbs require a current-limiting resistor for proper operation. Without a resistor, the current through the bulb would increase rapidly, potentially destroying it. The resistor ensures that the current stays within the bulb's safe operating range.
Here's a breakdown:
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Why a Resistor is Necessary: Neon bulbs exhibit negative resistance once they ignite. This means that as the voltage increases, the current also increases, leading to thermal runaway and bulb failure. A series resistor limits this current to a safe level.
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Resistor Value: The appropriate resistor value depends on the supply voltage and the desired current through the neon bulb. A common value for 120V or 240V AC applications is around 330kΩ, as mentioned in the reference.
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Placement: The resistor is connected in series with the neon bulb. This means the current flows through the resistor and then through the neon bulb (or vice versa).
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Built-in Resistors: Some neon bulbs come with a built-in resistor. If a neon bulb already has an internal resistor, you typically do not need to add an external one. You can usually determine if a bulb has a built-in resistor by checking its specifications or by testing its resistance with a multimeter (though a multimeter might not read well through the bulb depending on voltage).
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Indicating Power Off: As the reference suggests, one common use is as a power indicator in a switch. The neon bulb, along with its resistor, can be connected across the switch terminals, so when the switch is off, the neon bulb illuminates faintly, indicating that the circuit is not energized.
In summary, always use a resistor in series with a neon bulb unless it has a built-in resistor. This protects the bulb and ensures proper operation.
