![]() Thus, the threshold voltage sensing transistor provides the transistor switching means with a precise on/off operation. This circuit includes a capacitor that is charged through a serially connected charge circuit means which includes a brightness control resistor whose resistance is adjusted for a selected condition of brightness to determine the initial rate of charge of said capacitor voltage, the capacitor being periodically and briefly discharged through a discharge transistor.ĭuring the charge time the capacitor voltage is made to exceed a given threshold voltage Vth, and during discharge the capacitor voltage is reduced toward a reference level that is below Vth.Ī threshold voltage sensing transistor having its input coupled to the capacitor through a resistor voltage divider circuit and its output coupled to the input of the transistor switching means responds to the voltage across the capacitor and derives at its output a drive signal having a duty cycle that is dependent upon the relative time said capacitor voltage is above and below Vth. The operation of the transistor switching means is controlled as a function of a drive signal of approximately constant peak voltage derived from a capacitive charge-discharge circuit. The transistor switching means is controlled so as to provide a periodic on/off operation having a duty cycle that is varied to control the brightness of the display. These and other objects of the design are accomplished in accordance with one aspect of the design by a brightness control circuit for controlling the current flow from a source of energizing potential to an electronic display, the output of said potential source being coupled through a transistor switching means for supplying pulses of approximately constant peak current to the display elements. It is accordingly one object of the design to provide an improved brightness control circuit for LED and comparable electronic displays that provides a continuous control of the display elements over a wide range of brightness levels, extending particularly into the low brightness region.Īnother object of the design is to provide a brightness control circuit that provides uniform illumination from the display elements over a wide range of brightness levels.Ī further object of the design is to provide a brightness control circuit which is of relatively simple circuit configuration and may be inexpensively constructed.Īnother object of the design is to provide a brightness control circuit that is highly reproducible on a mass production basis. Summary of the Led Brightness Control Circuit As a related matter, the control circuit may be subject to temperature instabilities and excessive variations in component tolerances, giving rise to a nonuniform illumination from the display elements. ![]() In addition to being inefficient and wasteful of energy, these forms of control have a limited range over which the illumination can be linearly controlled and tends to turn off completely at low brightness. ![]() This is normally done by adjusting a resistance through which the energizing current flows, or by adjusting the supply voltage as applied through an emitter follower circuit. In the more common type of brightness control circuit for electronic displays, the current supplied to the display elements is controlled as a function of the amount of illumination desired from the display. The design pertains to electronic displays and to control circuitry for controlling the light output of these displays. Demystifying Analog-to-Digital Conversion: An Introduction to Arduino ADCĮxecutive Summary of the Led Brightness Control CircuitĪ brightness control circuit for (LED) displays, or comparable electronic displays that are energized from a source of DC potential that supplies periodic pulses of constant peak current to the display elements, the display brightness being controlled as a function of the pulse duty cycle so as to achieve a uniform and continuous control of the display over a relatively wide range of brightness levels, extending particularly into the lower brightness region.Įnergizing current is coupled to the display by a transistor switching means actuated at a given frequency and with a duty cycle that is a function of the brightness control setting.īackground of the Led Brightness Control Circuit ![]()
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