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Lamp brightness control circuit with ambient light compensation

  • US 5,581,158 A
  • Filed: 04/03/1995
  • Issued: 12/03/1996
  • Est. Priority Date: 09/21/1989
  • Status: Expired due to Fees
First Claim
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1. A lighting control system for gas discharge lamps, comprising:

  • an inverter circuit having a control input, a power input, and a plurality of switching mechanisms connected to alternately provide positive and negative voltage to a gas discharge lamp load, with the switching mechanisms controlled to vary a duty cycle of power supplied from said power input to the lamp load in response to the level of a low-power, variable DC control input voltage applied to the control input;

    a control circuit comprising control pulse generating means for generating control pulses of variable duty cycle;

    brightness control means connected to the control pulse generating means for setting the desired brightness of the load; and

    integrating means, connected between the inverter circuit control input and the control pulse generating means, for integrating the variable-width control pulses of the control pulse generating means to produce the variable DC control input voltage to the control input of the inverter circuit;

    an ambient light sensing circuit connected to the control pulse generating means for sensing the ambient light level and producing a variable control output depending on the ambient light level;

    wherein the control pulse generating means varies the duty cycle of the control pulses with the control output of the ambient light sensing circuit such that the brightness of the gas discharge lamp load is decreased when the amount of available ambient light increases.

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