EP0239247A1
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Heater control apparatus for liquid crystal display with integral heater
Assignee: Honeywell Inc
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Filing: 1987-02-25
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Granted: —
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Expires: 2007-02-25
Abstract
Abstract A heater control circuit for the integral heater (l9) of a liquid crystal display comprising solid state switches (4l, 42) that simultaneoulsy connect and disconnect the high side and low side of the heater from power and ground, respectively, in response to display temperature. A bleed resistor (49) is connected between the heater (l9) and ground to bleed off accumulated charge that would erroneously drive one of the solid state switches into conduction.
Inventors
- 👤 Gerald King Franklin
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 13:11
CPC Classifications
G; G02; G02F; G02F1/00; G02F1/01; G02F1/13; G02F1/133; G02F1/1333; G02F1/133382; G05; G05D; G05D23/00; G05D23/19; G05D23/1906; G05D23/1909
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
191 words
Heater control apparatus for use with a liquid crystal display having a heater (l9) integral therewith, the heater having an electrical input and an electrical output, in use current flowing between the electrical input and the electrical output resulting in heating of the heater, and comprising a source (40) of electrical potential for providing the current to the electrical input, characterised in that the apparatus further comprises return means for providing a return path for the current from the electrical output, first switch means (4l) for switchably coupling the source of electrical potential to the electrical input, second switch(42) means for switchably coupling the return means to the electrical output, and actuating means (46) coupled to the first and second switch means (4l, 42) for simultaneously actuating the first and second switch means for coupling the source of electrical potential to the electrical input and for coupling the return means to the electrical output when the heater is to be actuated, and for simultaneously deactuating the first and second switch means for decoupling the source of electrical potential from the electrical input and decoupling the return means from the electrical output.
Claim 2
Dependent Claim
191 words
Heater control apparatus for use with a liquid crystal display having a heater (l9) integral therewith, the heater having an electrical input and an electrical output, in use current flowing between the electrical input and the electrical output resulting in heating of the heater, and comprising a source (40) of electrical potential for providing the current to the electrical input, characterised in that the apparatus further comprises return means for providing a return path for the current from the electrical output, first switch means (4l) for switchably coupling the source of electrical potential to the electrical input, second switch(42) means for switchably coupling the return means to the electrical output, and actuating means (46) coupled to the first and second switch means (4l, 42) for simultaneously actuating the first and second switch means for coupling the source of electrical potential to the electrical input and for coupling the return means to the electrical output when the heater is to be actuated, and for simultaneously deactuating the first and second switch means for decoupling the source of electrical potential from the electrical input and decoupling the return means from the electrical output.
Claim 3
Dependent Claim
35 words
Apparatus according to claim l, characterised in that it further includes bleed path means (49) coupled between the heater (l9) and the return means for bleeding accumulated charge from the heater to the return means.
Claim 4
Dependent Claim
26 words
Apparatus according to claim l or 2, characterised in that the bleed path means comprises resistor means connected between the electrical input and the return means.
Claim 5
Dependent Claim
17 words
Apparatus according to any of the preceding claims, characterised in that the return means comprises electrical ground.
Claim 6
Dependent Claim
35 words
Apparatus according to any of the preceding claims, characterised in that the first switching means comprises a bipolar transistor (4l) coupling the source of electrical potential (40) to the electrical input of the heater (l9).
Claim 7
Dependent Claim
43 words
Apparatus according to claim 5, characterised in that the bipolar transistor comprises a PNP transistor (4l) with an emiter connected to the source of electrical potential (40), a collector connected to the electrical input, and a base responsive to the actuating means (46).
Claim 8
Dependent Claim
30 words
Apparatus according to any of the preceding claims, characterised in that the second switching means comprises a field effect transistor (42) coupled between the electrical output and the return means.
Claim 9
Dependent Claim
40 words
Apparatus according to claim 7, characterised in that the field effect transistor comprises a MOSFET (42) with a source connected to the electrical output, a drain connected to the return means, and a gate responsive to the actuating means (46).
Claim 10
Dependent Claim
72 words
Apparatus according to claim 7 when appended to claim 5, characterised in that the return means comprises electrical ground and the apparatus further includes bleed resistor means (49) coupled between the heater (l9) and ground for bleeding accumulated charge from the heater to ground, the resistor having the largest resistance value that maintains the bipolar transistor (4l) in a non-conducting state when the actuating means (46) is deactuating the first switching means.
Claim 11
Dependent Claim
43 words
l0. Apparatus according to any of the preceding claims, characterised in that the actuating means comprises a heater control (46) for simultaneously actuating and deactuating the first and second switch means (4l, 42) in response to the temperature of the liquid crystal display.
References Cited (Backward Citations)
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