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Lamp bulb having integrated RFI suppression and method of restricting RFI to selected level

  • US 5,504,395 A
  • Filed: 03/04/1994
  • Issued: 04/02/1996
  • Est. Priority Date: 03/08/1993
  • Status: Expired due to Fees
First Claim
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1. In an incandescent lamp having a translucent housing and a filament within the housing for emitting light when energized by electrical current from an AC power source passing through the filament, an improvement in combination therewith comprising:

  • a current change limiting element, comprising of an inductor assembly, located within the lamp and electrically connected to the filament and operative to limit the rate of change in current per change in time (di/dt) passing through the filament to a predetermined di/dt value in response to a substantially instantaneous change in voltage from the AC power source applied substantially instantaneously across the filament, the predetermined di/dt value limiting radio frequency interference (RFI) inherently emitted as a result of the di/dt in the filament in response to the substantially instantaneous change in voltage, the predetermined di/dt value having a value no greater than that value calculated according to the equation;

    ##EQU16## where;

    C is a maximum permitted current amplitude;

    Nn is 120 times an integer, n, where n represents the nth harmonic of the signal;

    ω

    is a value of the frequency at which electrical current is passed through the filament;

    t2 -t1 is a time differential between the time point t1 when the substantially instantaneous change in voltage is applied across the current change limiting element and the time point t2 when the di/dt reaches a maximum magnitude; and

    Ip is a value of a peak current level of the electrical current passing through the filament, established by the maximum value of the voltage of the AC power source and a resistance of the filament.

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