Gregory A Harris

US Patent:

50498690, Sep 17, 1991

Filed:

Jun 19, 1989

Appl. No.:

7/368257

Inventors:

Gregory W. Harris - Everett WA

Assignee:

Korry Electronics Company - Seattle WA

International Classification:

G09G 500

US Classification:

34081501

Abstract:

A dimming circuit (10) for use with an illuminated dual display (12) of an aircraft instrument is provided. A voltage divider (14) divides a variable supply voltage, V. sub. S, produces an input voltage, V. sub. IN, and applies V. sub. IN to one input of a switch (16). A threshold voltage circuit (15) receives the V. sub. S voltage and produces a reference voltage, V. sub. REF, and a lower magnitude supply voltage, V'. sub. S. A reference comparator (OA3) compares the V. sub. REF and V'. sub. S voltages and produces a threshold voltage, V. sub. T. The V. sub. T voltage is applied to a second input of the switch (16). A first comparator (OA1) in the switch (16) produces a low output voltage when the V. sub. T voltage exceeds the V. sub. IN voltage and causes a first lamp (L1) to brightly illuminate a first indicia (24).