Digital control system for LCD backlights
View Patent ↗Present invention provides an apparatus and a method for digital control of a backlight system in an LCD display. More specifically, the system utilizes a control system in embedded firmware and a mixed signal micro controller unit (MCU) to allow servo digital control of the operation of the backlight system. The MCU provides multiple input and output ports. The ports operate digital and analog signals, which connect a processor to the backlight system and allow the processor to operate the functions of the inverter and the lamps. The embedded firmware control implements digital servo functions and several algorithms used to precisely and automatically set lamp operation, control individual lamps, compensate for aging, perform diagnostics, optimize power consumption and automate manufacturing tests.
1. An apparatus, comprising:
an inverter configured to generate a secondary voltage, wherein the secondary voltage is generated, by a switch configured to convert a direct current input into an analog current output;
a multiplexer coupled to the inverter and configured to receive a feedback signal sensed from the secondary voltage;
an analog-to-digital converter coupled to the multiplexer and configured to convert the feedback signal into a digital feedback signal; and
a pulse width modulator coupled to the analog-to-digital converter and configured to drive the switch with a pulse width modulated signal based, on the digital feedback signal, wherein the pulse width modulated signal is configured to control the secondary voltage, wherein the pulse width modulator is further configured to provide a pulse width modulated signal to one or more lamp control circuits, wherein the pulse width modulated signal is switched on and off at a determined duty cycle to alter an impedance of the one or more lamp control circuits.
2. The apparatus of claim 1 , further comprising a voltage sense resistor coupled to both the inverter and the multiplexer and configured to sense a magnitude of the secondary voltage and provide the feedback signal.
3. A method, comprising:
generating a secondary voltage at an output of an inverter, wherein the secondary voltage is generated by switching a direct current through a switch to convert the direct current into an alternating current;
receiving, a feedback signal sensed from the secondary voltage;
multiplexing, the feedback signal in an analog multiplexer;
converting, the multiplexed feedback signal into a digital feedback signal via an A/D converter; and
driving the switch with a pulse width modulated signal in response to the digital feedback signal to control said generating;
driving one or more luminescent devices with a current based on the secondary voltage generated at the output of the inverter.
4. The method of claim 3 , further comprising measuring light output from the one or more luminescent devices to determine if the one or more luminescent devices are turned on.
5. The method of claim 4 , wherein said measuring comprises receiving a current feedback signal from the one or more luminescent devices, and wherein the current feedback signal is used to determine the light output.
6. The method of claim 4 , wherein said measuring comprises receiving a light output signal from a photosensor, and wherein the light output signal is used to determine the light output.
7. The method of claim 3 , further comprising controlling the current through the one or more luminescent devices by changing an impedance of the one or more luminescent devices.
8. The method of claim 3 , further comprising compensating for degradation of the one or more luminescent devices by adjusting the secondary voltage.