Apparatus and method to provide a hybrid linear/switching current source, such as for high-efficiency, wide dimming range light emitting diode (LED) backlighting

An apparatus to provide power to a load, the apparatus comprising:

• a pulse wave modulation (PWM) subsystem to generate a PWM enable signal that has a duty cycle that includes a first portion and a second portion;
• a first control unit coupled to said PWM subsystem to control a linear power supply to supply current to said load to cause said load to generate light during an initial part of said first portion;
• and
• a second control unit coupled to said PWM subsystem to control a switching power supply to supply a current to said load to cause said load to continue to generate light during a remainder part of said first portion that is subsequent to said initial part of said first portion, said first control unit being adapted to deactivate said linear power supply during said remainder part of said first portion, said second control unit being adapted to deactivate said switching power supply during said second portion of said duty cycle.

A system, comprising:

• a backlight light emitting diode (LED) display device;
• a linear power supply coupled to said LED display device;
• a switching power supply coupled to said LED display device;
• a pulse wave modulation (PWM) subsystem to generate a PWM enable signal that has a duty cycle that includes an ON portion and an OFF portion;
• a first control unit coupled to said PWM subsystem to control said linear power supply to supply current to said LED display device during an initial part of said ON portion of the duty cycle;
• and
• a second control unit coupled to said PWM subsystem to control said switching power supply to supply a current to said LED display device during a remainder part of said ON portion that is subsequent to said initial part of said ON portion, said first control unit being adapted to deactivate said linear power supply during said remainder part of said ON portion, said second control unit being adapted to deactivate said switching power supply during said OFF portion of said duty cycle.

A method to provide power to loads, the method comprising:

• producing a drive signal indicative of an amplitude;
• scaling down the drive signal to produce a scaled down drive signal;
• applying the scaled down drive signal to a linear power supply error circuit at a first time;
• producing a linear power supply error signal indicative of a difference between the scaled down drive signal and a current feedback signal indicative of a magnitude of a current being supplied to a load;
• applying the linear power supply error signal to drive a linear power supply to supply current to the load;
• applying the drive signal to a switching power supply error circuit at a second time, the second time delayed from the first time;
• producing a switching power supply error signal indicative of a difference between the drive signal and the current feed back signal indicative of the magnitude of the current being supplied to the load;
• and
• applying the switching power supply error signal to drive a switching power supply to supply current to the load.