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US 9,288,859 B2Granted
Light emitting diode driving circuit, display device, lighting device, and liquid crystal display device
AssigneeShapr Kabushiki Kaisha
InventorMasahiro Hirokane
Life of this patent
Estimating the term…
Abstract
As a result of being provided with an enable signal generating unit that supplies, to an LED driver, an enable signal that is dependent on a low state period of a PWM signal, it is possible to realize a light emitting diode driver circuit that can suppress a booster circuit starting up suddenly and an excess current flowing in a power source in the case where the PWM signal enters a high state (on state) after having been held in a low state (off state) for a prescribed period or longer.
Claims9
A light emitting diode driver circuit, comprising:
- a control unit receiving a pulse width modulation signal and controlling a booster circuit for adjusting a luminance of a light emitting diode in accordance with said pulse width modulation signal;
- and
- an enable signal generating unit that generates an enable signal for turning said control unit ON/OFF and supplies said enable signal to said control unit, the enable signal generating unit generating a signal that turns said control unit OFF as the enable signal when said pulse width modulation signal is LOW for a prescribed period or longer,
- wherein said control unit includes a soft start unit that, when a signal that turns the control unit from OFF to ON is received as the enable signal, causes the control unit to control said booster circuit such that said booster circuit is driven with a soft start,
- wherein the enable signal generating unit includes a counter circuit,
- wherein the enable signal generating unit receives the pulse width modulation signal, and a control signal that is not dependent on said pulse width modulation signal, and
- wherein, when said pulse width modulation signal is LOW for the prescribed period or longer, said enable signal generating unit generates said enable signal in accordance with said control signal and a counter output signal that is output from said counter circuit.
4 more elements
A light emitting diode driver circuit, comprising:
- a control unit receiving a pulse width modulation signal and controlling a booster circuit for adjusting a luminance of a light emitting diode in accordance with said pulse width modulation signal;
- and
- an enable signal generating unit that generates an enable signal for turning said control unit ON/OFF and supplies said enable signal to said control unit, the enable signal generating unit generating a signal that turns said control unit OFF as the enable signal when said pulse width modulation signal is LOW for a prescribed period or longer,
- wherein said control unit includes a soft start unit that, when a signal that turns the control unit from OFF to ON is received as the enable signal, causes the control unit to control said booster circuit such that said booster circuit is driven with a soft start,
- wherein said enable signal generating unit includes:
- an active element that outputs a power source voltage in accordance with the pulse width modulation signal;
- and
- an AND circuit that receives said power source voltage that is output from said active element, and a control signal that is not dependent on said pulse width modulation signal,
- wherein wiring through which said power source voltage that is output from said active element passes until being input to said AND circuit is provided with a resistor and a capacitor for adjusting a time during which said power source voltage drops when said power source voltage is not output from said active element,
- wherein, when said power source voltage is not output from said active element, a value of said resistor and a value of said capacitor are set such that said power source voltage of said wiring becomes equal to or less than a threshold voltage of said AND circuit after said prescribed period or longer, and
- wherein said enable signal is output from said AND circuit.
8 more elements
A light emitting diode driver circuit, comprising:
- a control unit receiving a pulse width modulation signal and controlling a booster circuit for adjusting a luminance of a light emitting diode in accordance with said pulse width modulation signal;
- and
- an enable signal generating unit that generates an enable signal for turning said control unit ON/OFF and supplies said enable signal to said control unit, the enable signal generating unit generating a signal that turns said control unit OFF as the enable signal when said pulse width modulation signal is LOW for a prescribed period or longer,
- wherein said control unit includes a soft start unit that, when a signal that turns the control unit from OFF to ON is received as the enable signal, causes the control unit to control said booster circuit such that said booster circuit is driven with a soft start,
- wherein said enable signal generating unit includes:
- an active element that outputs an anode voltage of said light emitting diode in accordance with a power source voltage;
- and
- an AND circuit that receives said anode voltage that is output from said active element and a control signal that is not dependent on said pulse width modulation signal,
- wherein wiring through which said anode voltage that is output from said active element passes until being input to said AND circuit is provided with a resistor and a capacitor for adjusting a time during which said anode voltage that is output from said active element drops,
- wherein a value of said resistor and a value of said capacitor are set such that said anode voltage of said wiring becomes equal to or less than a threshold voltage of said AND circuit after said prescribed period or longer, and
- wherein said enable signal is output from said AND circuit.
8 more elements
Dependencies are inferred from the claim text.