Patent US4952949A successfully refreshed from Google Patents.
US4952949A
Expired / Lapsed
US
⏱️ 0.0 years remaining
LED printhead temperature compensation
Assignee: Avago Technologies International Sales Pte Ltd
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Filing: 1989-11-28
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Granted: 1990-08-28
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Expires: 2009-11-28
Abstract
Abstract The light output of light emitting diodes on an LED printhead for a photosensitive printer is temperature compensated so that light output remains constant regardless of temperature changes of the LED chips. An LED chip has a plurality of exposure LEDs and a dummy LED. The voltage across the dummy LED is sensed and combined with an adjustable reference voltage. This provides the input to an op-amp, the output of which provides a chip reference voltage which controls the current to the LEDs.
Inventors
- 👤 John J. Uebbing
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 21:50
CPC Classifications
B; B41; B41J; B41J2/00; B41J2/435; B41J2/447; B41J2/45; G; G06; G06K; G06K15/00; G06K15/02; G06K15/12; G06K15/1238; G06K15/1242; G06K15/1247
Claims Analysis
Total Claims: 29
Claim 1
Independent Claim
70 words
A method for compensating for temperature variations in a light emitting diode printhead for a photosensitive printer comprising the steps of: sensing the voltage across a dummy light emitting diode on the same chip with a plurality of exposure diodes; and adjusting a chip reference voltage which controls LED current as a function of the sensed voltage for compensating for changes in the temperature of the dummy light emitting diode.
Claim 2
Independent Claim
70 words
A method for compensating for temperature variations in a light emitting diode printhead for a photosensitive printer comprising the steps of: sensing the voltage across a dummy light emitting diode on the same chip with a plurality of exposure diodes; and adjusting a chip reference voltage which controls LED current as a function of the sensed voltage for compensating for changes in the temperature of the dummy light emitting diode.
Claim 3
Dependent Claim
46 words
A method as recited in claim 1 wherein the adjusting step comprises combining the sensed voltage and a constant voltage for obtaining a compensation voltage, and applying the compensation voltage to the input of an op-amp, the output of the op-amp providing the chip reference voltage.
Claim 4
Dependent Claim
31 words
A method as recited in claim 2 further comprising the step of adjusting the gain of the op-amp as a function of variation of LED light output with respect to temperature.
Claim 5
Dependent Claim
43 words
A method as recited in claim 2 wherein the adjusting step comprises: applying the compensation voltage to the inverting input of an op-amp; and adjusting the gain of the op-amp based on the light output of the LEDs as a function of temperature.
Claim 6
Dependent Claim
22 words
A method as recited in claim 1 comprising sensing the voltage across the dummy LED when the exposure LEDs are turned off.
Claim 7
Dependent Claim
24 words
A method as recited in claim 1 comprising the step of storing the reference voltage during an interval when the exposure LEDs are enabled.
Claim 8
Dependent Claim
47 words
A method as recited in claim 1 comprising the steps of: storing a reference voltage in a capacitor; storing the sensed voltage in a capacitor; and connecting both capacitors in parallel to the input of an op-amp, the output of the op-amp providing the chip reference voltage.
Claim 9
Dependent Claim
30 words
A method as recited in claim 7 wherein each of the capacitors is adjustable and is set at a capacitance value which collectively represents the temperature coefficient of the LEDs.
Claim 10
Independent Claim
58 words
A method for compensating for temperature variations in a light emitting diode chip having a plurality of exposure diodes comprising the steps of: sensing the voltage across a dummy diode; adjusting an amplifier output as a function of the sensed voltage; and applying the amplifier output as a chip reference voltage for controlling current to the exposure diodes.
Claim 11
Independent Claim
58 words
A method for compensating for temperature variations in a light emitting diode chip having a plurality of exposure diodes comprising the steps of: sensing the voltage across a dummy diode; adjusting an amplifier output as a function of the sensed voltage; and applying the amplifier output as a chip reference voltage for controlling current to the exposure diodes.
Claim 12
Dependent Claim
24 words
A method as recited in claim 9 wherein the dummy diode comprises a light emitting diode on the same chip as the exposure diodes.
Claim 13
Dependent Claim
31 words
A method as recited in claim 9 wherein the adjusting step comprises adjusting the gain of the amplifier as a function of variation of LED light output with respect to temperature.
Claim 14
Dependent Claim
23 words
A method as recited in claim 9 wherein the adjusting step comprises capacitively connecting the sensed voltage to the input of the amplifier.
Claim 15
Dependent Claim
42 words
A method as recited in claim 12 wherein the step of capacitively coupling comprises: storing the sensed voltage in a first capacitor; storing a constant voltage in a second capacitor; and connecting both capacitors in parallel to the input of the amplifier.
Claim 16
Dependent Claim
30 words
A method as recited in claim 9 wherein the adjusting step comprises adjusting the gain of the amplifier in response to variation LED light output as a function of temperature.
Claim 17
Dependent Claim
36 words
A method as recited in claim 9 wherein the adjusting step comprises combining the sensed voltage and a constant voltage for providing a compensation voltage, and applying the compensation voltage to the input of the amplifier.
Claim 18
Dependent Claim
50 words
A method as recited in claim 9 comprising the steps of: storing a reference voltage in a first capacitor; storing the sensed voltage in a second capacitor; and connecting both capacitors in parallel to the inverting input of an op-amp, the output of the op-amp providing the chip reference voltage.
Claim 19
Dependent Claim
105 words
A temperature compensated LED printhead for a photosensitive printer comprising: a light emitting diode chip having a plurality of exposure LEDs; means for generating a compensation voltage bearing a known relation to the temperature of the chip; a compensation op-amp; means for applying the compensation voltage to the inverting input of the compensation op-amp; means for adjusting the op-amp gain in response to changes in LED light output as a function of temperature; means for generating a chip reference voltage as a function of the output of the op-amp; and means for controlling current through the exposure LEDs in response to the chip reference voltage.
Claim 20
Dependent Claim
105 words
A temperature compensated LED printhead for a photosensitive printer comprising: a light emitting diode chip having a plurality of exposure LEDs; means for generating a compensation voltage bearing a known relation to the temperature of the chip; a compensation op-amp; means for applying the compensation voltage to the inverting input of the compensation op-amp; means for adjusting the op-amp gain in response to changes in LED light output as a function of temperature; means for generating a chip reference voltage as a function of the output of the op-amp; and means for controlling current through the exposure LEDs in response to the chip reference voltage.
Claim 21
Dependent Claim
39 words
A temperature compensated LED printhead as recited in claim 17 wherein the means for generating a compensation voltage comprises a dummy LED on the chip, and the compensation voltage is a function of the voltage across the dummy LED.
Claim 22
Dependent Claim
54 words
A temperature compensated LED printhead as recited in claim 17 wherein the means for generating a compensation voltage comprises: a diode having a voltage drop which is a function of temperature; means for sensing a voltage across the diode; and means for combining the voltage with a constant voltage for generating the compensation voltage.
Claim 23
Dependent Claim
56 words
A temperature compensated LED printhead as recited in claim 17 wherein the means for applying the compensation voltage to the compensation op-amp comprises: first capacitive means for storing the compensation voltage; second capacitive means for storing the sensed voltage; and switching means for switching both capacitive means in parallel to the input of the compensation op-amp.
Claim 24
Dependent Claim
68 words
A temperature compensated LED printhead for a photosensitive printer, having a plurality LED chips on the printhead and a plurality of exposure LEDs on each chip comprising: a dummy diode for each chip; means for passing current through the diode; means for sensing voltage across the diode; and means for adjusting the current passed through the exposure LEDs on the respective chip in response to the sensed voltage.
Claim 25
Dependent Claim
68 words
A temperature compensated LED printhead for a photosensitive printer, having a plurality LED chips on the printhead and a plurality of exposure LEDs on each chip comprising: a dummy diode for each chip; means for passing current through the diode; means for sensing voltage across the diode; and means for adjusting the current passed through the exposure LEDs on the respective chip in response to the sensed voltage.
Claim 26
Dependent Claim
21 words
A temperature compensated LED printhead as recited in claim 21 wherein the dummy diode comprises a dummy LED on each chip.
Claim 27
Dependent Claim
69 words
A temperature compensated LED printhead as recited in claim 21 comprising: a capacitor selectively connectable across the diode for storing the sensed voltage; means for combining the sensed voltage with a constant voltage for providing a compensation voltage; an amplifier; and means for applying the compensation voltage to the input of the amplifier, the current passed through the exposure LEDs being a function of the output of the amplifier.
Claim 28
Dependent Claim
42 words
A temperature compensated LED printhead as recited in claim 23 wherein: the means for combining comprises an adjustable capacitor for storing the constant voltage; and means for applying the voltages stored in both capacitors in parallel to the input of the amplifier.
Claim 29
Dependent Claim
27 words
A temperature compensated LED printhead as recited in claim 24 wherein the amplifier comprises an op-amp and comprising means for applying a feedback capacitor across the op-amp.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-08-27 | 1994-02-26 | 1994-08-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-08-27 | 1998-02-26 | 1998-08-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-08-27 | 2002-02-26 | 2002-08-28 | $7700.00 | Window Closed / Lapsed |