Apparatus and method to provide a hybrid linear/switching current source, such as for high-efficiency, wide dimming range light emitting diode (LED) backlighting
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United States of America Patent
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May 19, 2009
Grant Date -
Oct 30, 2008
app pub date -
Apr 27, 2007
filing date -
Apr 27, 2007
priority date (Note) -
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Abstract
A hybrid power supply provides powers to a load, such as a light emitting diode (LED) backlight display, using pulse wave modulation (PWM) enable signal to control activation of a linear power supply and a switching power supply. During an initial part of an active portion of a duty cycle of the PWM enable signal, the linear power supply is activated to supply the load with constant current. During the remainder of the active portion of the duty cycle of the PWM enable signal, the linear power supply is deactivated and the switching power supply is activated to provide current to the load. A bias current and voltage may be provided to the LED during an inactive portion of the duty cycle of the PWM enable signal. The hybrid power supply combines the high efficiency of the switching power supply with smooth dimming control at low luminance of the linear power supply.
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