Abstract: A liquid crystal display (LCD) system having LED backlight luminance sensing is disclosed. An array of LEDs in a backlighting position includes a plurality of LED strings. At least one LED from at least one string is identified as a sampling LED. The light emitted from the sampling LED is detected via an optical path using a light sensor. The reading from the sensor is contrast with a command, which results in a power compensation to the array accordingly. In one embodiment, the system includes a sampling enclosure encasing the sampling LED and light sensor. The sampling LED's direction of emission is altered from the string and reflected from the inside of the enclosure. In another embodiment, the system includes a direct sensing optical path between the light sensor and the sampling LED.

Abstract: A circuit and method for providing a linear power to a load uses pulse modulation technique where the frequency and pulse width of the pulse width modulated waveform driving the load are varied simultaneously. In one aspect of the disclosure, a pulse width modulator circuit is responsive to a command drive signal for producing the pulse width waveform the width of the pulses varying accordingly. In addition, a frequency control circuit that is also responsive to the command drive signal provides a control current to the pulse width modulator circuit wherein the frequency of the waveform is varied as the pulse widths are varied.

Abstract: A liquid crystal display (LCD) system having LED backlight luminance sensing is disclosed. An array of LEDs in a backlighting position includes a plurality of LED strings. At least one LED from at least one string is identified as a sampling LED. The light emitted from the sampling LED is detected via an optical path using a light sensor. The reading from the sensor is contrast with a command, which results in a power compensation to the array accordingly. In one embodiment, the system includes a sampling enclosure encasing the sampling LED and light sensor. The sampling LED's direction of emission is altered from the string and reflected from the inside of the enclosure. In another embodiment, the system includes a direct sensing optical path between the light sensor and the sampling LED.

Abstract: A control system and method for supplying a constant RMS voltage to a load includes a outer control loop for monitoring a characteristic variable of the system and an inner control loop for maintaining the power delivered to the load as a function of the received input power. A pulse width modulator (PWM) coupled to both control loops delivers pulses representative of an unregulated input voltage duty cycle. The inner control loop compares the duty cycle representation of the input voltage with a duty cycle representation of the pulse and generates a control signal to the PWM accordingly.

Abstract: A programmable control circuit is disclosed for generating a programmable power curve and ramp. The circuit includes an amplifier having both positive and negative feedback. The positive feedback including a time lag component and the negative feedback including a gain component. The circuit output is easily programmable by varying the component values and/or the input signal. In one embodiment, the rate of change of the control circuit's output waveform may be modified. In another embodiment, the circuit controls the start-up power supplied to a load. In yet another embodiment, the circuit is a waveform generator.

Abstract: An apparatus converts m-bit digital data having a scale factor of K.sub.1 to n-bit digital data having a scale factor of K.sub.2. The apparatus comprises a digital to analog converter which receives the m-bit digital data, for outputting a first analog signal representative of a value associated with the m-bit digital data. An amplifier receives the first analog signal multiplies it by a factor, and outputs a second analog signal. The factor of the amplifier is K.sub.2 /K.sub.1, such that the second analog signal has a value with the scale factor of K.sub.2 associated therewith. An analog to digital converter receives the second analog signal, and converts the second analog signal to the n-bit digital data. The n-bit digital data has the scale factor of K.sub.2 associated therewith, the value representative of the n-bit digital data being essentially equal in the example of the present application to the value representative of the m-bit digital data, however, this is not always a requirement.

Abstract: A driver apparatus for driving one or more electrical loads includes an oscillator for providing an input signal. An amplifier amplifies the input signal. A power transformer has a primary winding for receiving the amplified input signal and at least one secondary winding for providing a drive signal to drive one or more electrical loads. The driver apparatus may include a center tap for the secondary windings or a precision resistive network for providing a pair of diametrically symmetrical drive signals at each secondary winding. A drive signal from one of the secondary windings is compared to a reference signal in an automatic gain control loop for application to the oscillator. An average drive signal could also be derived from one output from each secondary winding to be compared to the reference signal for forming the gain automatic control loop.

Abstract: A buffer comparator receives input pulses and produces buffer output signals that drive first and second output comparators arranged to operate as an amplitude-sensitive logic circuit that produces a high level output signal when and only when the internal driving signals have an amplitude between first and second threshold levels. In one embodiment, the output of the buffer comparator is applied directly to the non-inverting input terminal of the first logic circuit comparator and through a low resistance resistor to an R-C network and the inverting terminal of the second logic circuit comparator. The remaining input terminals on the logic comparators are connected to a multiple voltage divider that provides lower and upper threshold voltages to the respective comparators. An input pulse applied to the buffer comparator initiates an internal driving signal that charges the capacitor in the R-C network exponentially.

Abstract: A bi-directional driver system for an electrical load operable in response to two independent logic command signals provides a means for selecting the direction of current flow in the load when driven by the external command. A bridge circuit employs inputs to dual transistor switches operating in the saturated mode in series with the electrical load, cooperating with common emitter transistor linear amplifiers and diodes, and biased by the input logic signal so as to drive the load current in a predetermined direction. The circuit provides protection from undesired power supply current surges when logic command signals are applied to both inputs, and from transients due to failure of a saturated transistor switch at one input to cease conducting before the application of a command signal to the second input. Embodiments for inductive loads and annunciator lamps are described.