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Light-emitting diode display system

  • US 4,887,074 A
  • Filed: 01/20/1988
  • Issued: 12/12/1989
  • Est. Priority Date: 01/20/1988
  • Status: Expired due to Term
First Claim
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1. A display system, including:

  • at least one LED;

    a drive circuit having a finite, nonzero RC time constant, including a capacitor connected in series with the at least one LED, and capable of driving the at least one LED into a light-emitting mode in response to an alternating voltage signal, in which light-emitting mode each driven LED emits a train of light pulses separated by intervals of substantially zero light intensity, and in which light-emitting mode the drive circuit introduces a phase shift between the alternating voltage signal and the current through each driven LED to increase the duration of the substantially zero light intensity intervals beyond the duration said intervals would have if the capacitance of the drive circuit were zero, so as to reduce the average temperature of each LED in the light emitting mode below the average temperature each said LED would have if the capacitance of the drive circuit were zero;

    a switch coupled with the drive circuit, and capable of switching in response to control signals between an on position in which the alternating voltage signal is supplied through the switch to the drive circuit, and an off position preventing the alternating voltage signal from propagating through the switch to the drive circuit; and

    a drive controller coupled to the switch, for generating control signals and supplying said control signals to said switch, wherein each of the control signals coincides with a zero crossing of the alternating voltage signal.

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