Direct drive backlight system

A power conversion circuit for driving a fluorescent lamp, the circuit comprising:

• a controller which generates control signals having active states and inactive states, said controller varying the durations of the active states and the inactive states;
• a plurality of switching transistors coupled to a source of input power and responsive to said control signals to selectively conduct current from said source of input power;
• and
• a transformer having a primary winding directly coupled to said switching transistors to receive a substantially rectangular voltage signal from said switching transistors, said transformer having a secondary winding coupled to said fluorescent lamp to provide a sinusoidal current to said fluorescent lamp, wherein the controller is a pulse width modulating controller controlling current through said fluorescent lamp by modulating a duty cycle of said control signals, and wherein the pulse width modulating controller further comprises:
• an oscillator for generating a clock signal with fixed frequency;
• a current limit input for limiting a maximum amount of the current through the fluorescent lamp;
• a dimming input for controlling a dimming level of the fluorescent lamp;
• and
• a signal generating circuit responsive to the clock signal, the current limit input and the dimming input and generating the control signals to the plurality of switching transistors to provide pulse width modulated control signals responsive to the clock signal, the current limit input and the dimming input.

A power converter circuit for converting a power signal to drive a fluorescent lamp, the circuit comprising:

• a controller for providing control signals;
• a non-tuned driver network responsive to the control signals and coupled to receive the power signal, the driver network having a plurality of transistors coupled to the controller and a primary winding of a transformer coupled to the plurality of transistors;
• and
• a secondary winding of the transformer magnetically coupled to the primary winding to provide a sinusoidal current to the fluorescent lamp.

A method of converting a power signal to drive a fluorescent lamp, the method comprising the steps of:

• generating a clock signal with a fixed frequency;
• receiving a dimming level input;
• generating control signals for controlling a plurality of transistors by using the clock signal and the dimming level input;
• switching the plurality of the transistors by applying the control signals to the plurality of transistors;
• providing a rectangular wave voltage signal to a primary winding of a transformer through the switching of the plurality of transistors;
• and
• inducing a sinusoidal voltage across a secondary winding of the transformer magnetically coupled to the primary winding,
• wherein the plurality of transistors is coupled to receive the power signal.

An apparatus for converting a power signal to drive a fluorescent lamp, the apparatus comprising:

• means for generating a clock signal with a fixed frequency;
• means for receiving a dimming level input;
• means for generating control signals for controlling a plurality of transistors by using the clock signal and the dimming level input;
• means for switching the plurality of transistors by applying the control signals to the plurality of transistors;
• means for providing a rectangular wave voltage signal to a primary winding of a transformer through the switching of the plurality of transistors;
• and
• means for inducing a sinusoidal voltage across a secondary winding of the transformer coupled magnetically to the primary winding,
• wherein the plurality of transistors is coupled to receive the power signal.

A device for driving a fluorescent lamp, comprising:

• a controller configured to provide control signals;
• a non-tuned driver network, responsive to said control signals, configured to output a first signal;
• and
• a secondary network, responsive to said first signal, configured to provide a substantially sinusoidal current to said fluorescent lamp, wherein said non-tuned network operates at a non-resonating frequency.