Dimming circuit for dual display aircraft instruments

Details Dimming circuit for dual display aircraft instruments Dimming circuit for dual display aircraft instruments

1989-06-19

1991-09-17

Weldon, Ulysses

Communications: electrical

Visual indication

Movable

307350, 307358, 307362, 34081502, 34081503, 34081504, 315 77, 315296, G09G 500

Patent

active

050498690

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). A second comparator (OA2) in the switch (16) produces a low output voltage when the V.sub.T voltage is less than the V.sub.IN voltage, which causes a second lamp (L2) to dimly illuminate a second indicia (26). The illuminated first indicia (24) provides daytime illumination of the dual display (12) and the illuminated second indicia (26) provides nighttime illumination. A night vision goggle compatible filter (22) makes the indicia (26) readable by crew members wearing night vision goggles. The voltage divider (14) and threshold voltage circuit (15) operate to ensure a substantial difference between the values of the V.sub.IN and V.sub.T voltages, and thus, provide precise switching between daytime and nighttime illumination of the instrument (12).

REFERENCES:
patent: 4311994 (1982-01-01), Kuribayashi
patent: 4574276 (1986-03-01), Sato
patent: 4613770 (1986-09-01), Raab
patent: 4722028 (1988-01-01), Brannon et al.
patent: 4724375 (1988-02-01), Dittmar
patent: 4904991 (1990-02-01), Jones

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