System, apparatus, and method for driving light emitting diodes in low voltage circuits
First Claim
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1. A driver circuit, comprising:
- a voltage booster coupled to receive an input voltage and coupled to provide an output voltage having an increased magnitude relative to the input voltage;
a current source coupled to receive the input voltage and to provide a substantially constant current in response to the input voltage, the current source comprising a bias generation circuit coupled to provide a bias voltage in response to the input voltage and a current conduction device coupled to receive the bias voltage and coupled to provide the substantially constant current in response to the bias voltage; and
a component coupled to the voltage booster and the current source, wherein the voltage booster activates the component using the output voltage and the substantially constant current.
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Abstract
A system, apparatus, and method for allowing LED operation in circuits operating with power supply levels that are below the forward voltage limits of the LED. A first level of a modulated voltage signal is applied to charge a voltage increasing component in a first phase of operation. A second level of the modulated voltage signal is then summed with the voltage stored across the voltage increasing component to provide adequate forward potential across Light Emitting Diode (LED) for illumination. The second level of modulated voltage is also used to provide a source of constant forward current to be conducted by LED when in its luminescent state.
89 Citations
24 Claims
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1. A driver circuit, comprising:
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a voltage booster coupled to receive an input voltage and coupled to provide an output voltage having an increased magnitude relative to the input voltage; a current source coupled to receive the input voltage and to provide a substantially constant current in response to the input voltage, the current source comprising a bias generation circuit coupled to provide a bias voltage in response to the input voltage and a current conduction device coupled to receive the bias voltage and coupled to provide the substantially constant current in response to the bias voltage; and a component coupled to the voltage booster and the current source, wherein the voltage booster activates the component using the output voltage and the substantially constant current. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of controlling a luminescent state of a Light Emitting Diode (LED), comprising:
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receiving an input signal; boosting the input signal to form a boosted signal, comprising; generating a charging signal in response to a first phase of the input signal; increasing a potential stored across an energy storage device in response to the charging signal; and combining the input signal with the potential stored across the energy storage device in response to a second phase of the input signal; generating a substantially constant current from the input signal, comprising; forming a bias signal in response to the second phase of the input signal; and inducing a conductive state of a current control device in response to the bias signal, wherein the substantially constant current is proportional to the bias signal; and applying the boosted signal and the substantially constant current to illuminate the LED.
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10. A method of controlling backlighting associated with a display, comprising:
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storing charge from a power source in a first phase of operation when a bias voltage supplying at least one Light Emitting Diode (LED) is less than a forward voltage required by the LED, wherein the power source provides a voltage level lower than the forward voltage required by the LED; in a second phase of operation, combining an operating voltage with the stored charge to illuminate the LED using the combined voltage as the bias voltage; and alternating the first and second phases of operation to control the backlighting associated with the display. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. An environmental control system, comprising:
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a display controller coupled to the environmental control system to provide display information; a thermostat comprising an LCD coupled to receive the display information, and an LCD backlight system coupled to the LCD, the LCD backlight system comprising; a voltage booster coupled to receive a lighting control signal and coupled to provide an output signal having an increased magnitude of the lighting control signal; a current source coupled to receive the lighting control signal and coupled to provide a substantially constant current in response to the lighting control signal; and a Light Emitting Diode (LED) coupled to the voltage booster and the current source, wherein the voltage booster activates the LED using the output signal and the substantially constant current. - View Dependent Claims (18, 19, 20, 21, 22, 23)
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24. A Light Emitting Diode (LED) control circuit, comprising:
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means for storing charge from a power source in a first phase of operation when a bias voltage supplying at least one Light Emitting Diode (LED) is less than a forward voltage required by the LED, wherein the power source provides a voltage level lower than the forward voltage required by the LED; means for combining, in a second phase of operation, an operating voltage with the stored charge to illuminate the LED using the combined voltage as the bias voltage; and means for alternating the first and second phases of operation to control the backlighting associated with the display.
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Specification