Patent Application
20120217153
Power supplies used to power certain devices, such as electroluminescent (EL) backlights, generally need to provide additional power to increase brightness. Boosting the power may provide a brighter backlight, but it generally shortens the longevity of the EL.
In other applications it is also often necessary to increase power to increase the output of a device.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
The instant application relates to a power supply suitable for powering devices such as an electroluminescent (EL) backlight. In one embodiment, the power supply uses an inductor-capacitor (LC) tank circuit resonance designed to power an inorganic electroluminescent material, a power source, an electronic switching circuit, and a frequency generator and a pulse width encoder. This may allow increased brightness without a need for increasing the power provided.
These and other features and advantages of a self-tuning power supply will now be described with reference to drawings of certain embodiments, which are intended to illustrate and not to limit the instant application.
The present invention is described in detail below with reference to the attached drawing figures, wherein:
The subject matter of the present invention is described with specificity herein to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed subject matter might also be embodied in other ways, to include different steps or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies. Moreover, although the terms “step” and/or “block” may be used herein to connote different elements of methods employed, the terms should not be interpreted as implying any particular order among or between various steps herein disclosed unless and except when the order of individual steps is explicitly described.
In the following detailed description, references are made to the accompanying drawings that form a part hereof, and which show by way of illustration specific embodiments or examples. Referring now to the drawings, in which like numerals represent like elements through the several figures, aspects of a self-tuning power supply will be described.
An equation for determining an output frequency of an LC tank circuit 120 has three parameters: the frequency for stimulating the LC oscillator, measured in hertz or cycles per second; the inductance, measured in henries; and the capacitance, measured in farads.
Two of these three parameters may be determined in advance; frequency (f) may be preselected, and may be, for example, between 60 hz and 20 khz for EL backlight embodiments. The capacitance (C) of the EL C1 may be measured empirically using a capacitance meter. The value of the inductor (L) needed to obtain a particular resonance frequency in a specific LC tank circuit 120 may be calculated to provide a maximum brightness capability of a sheet of EL after fine tuning the frequency and duty cycle.
To accommodate our EL LC tank circuit's 120 external stimulus requirements, a switching circuit 130, an external adjustable power source 110, to supply adjustable voltage and current to the LC tank circuit 120 and to allow the EL brightness to be variable, and a precision frequency controlled generator circuit 140, to maintain resonant harmonics in the LC tank circuit.
(700 sqin)/(0.3 scm/sqin)=2,333 sqcm·2,333 sqcm*0.3 mA/sqcm=700 mA=0.7 A. And the wattage would be: 0.7 A*200V=14 W.
One skilled in the art will recognize that there are numerous design alterations and possibilities for each of these power supply blocks described above, a few of which are described below:
One skilled in the art will realize that other components may be used to provide similar functionality.
One embodiment of the LC tank circuit 215 uses a step-down transformer, with higher resistance wire selected for use as an inductor T1. A lower resistance wiring may be selected to provide a voltage suitable for a resonance detector 230.
A load for this embodiment may be an EL C2. Other loads beside an EL may also be driven by such a circuit.
One skilled in the art will realize that other components may be used to provide similar functionality.
In the example embodiment illustrated in
Various embodiments for an electronic switch 220 may include, by way of example and not limitation, a MOSFET, FET, SCR, TRIAC or fast switching BJT with a criteria being that the device be capable of handling the power consumption of a device being powered. It is this circuit which may supply the current sink to ground to pulsate the EL tank circuit. As with the components mentioned earlier, any higher power device will work so long as the minimum power constraints are satisfied. Heating up of this device may be of concern, in which case input impedance, ability to switch quickly, and power dissipation may be considered. R2 may limit the current draw on the timer circuit in order to ensure minimum stress on the output stage of whatever timer based circuit is used. One skilled in the art will realize that other components may be used to provide similar functionality.
A timer chip may be used as a time-based frequency generator 240 with a built-in pulse-width encoder:
A 555 timer IC may be used, by way of example and not limitation, since it may handle voltages up to about 15 VDC and may be designed to accommodate frequencies into the megahertz range with duty cycles up to 50%. In this example embodiment, values for R2, R3 and C3 are calculated per the equations that are supplied with the 555 timer IC's data sheet. Either R2 or R3 may be a variable potentiometer in order to allow for variation of the output's waveform. This allows such a circuit to be used as a pulse width encoder and it may be used to vary the on-time for the switching device, which may result in varying the brightness of the EL material. There are numerous oscillator timer circuits and IC's that duplicate the function of the 555 timer including SW programmable timers such as the CD4541 BE programable IC or the U2102B oscillator timer IC for example. Virtually any waveform can be used to switch a particular type of switching device but a square wave is the most commonly used since the pulse duration can be easily varied using any number of pulse width encoder designs. However, other embodiments may use different shapes or a combination of shapes for waveforms. One skilled in the art will realize that other components may be used to provide similar functionality.
The examples used in this application are for illustrative purposes only, and are not meant to restrict the scope of this application. The examples have primarily used AC induction motors and EL devices, such as EL backlights as devices that may be powered by a self-tuning power supply. However, other devices may also be powered by a self-tuning power supply as described herein. For example, a device to perform electrolysis may be run most efficiently when at its resonant frequency. Similarly, gas-discharge lamps may work best with a self-tuning power supply, which may adjust the operating frequency over time as components specifications change with temperature or wear over time. Other devices may also work more efficiently when operated at a resonant frequency.
While the detailed description above has been expressed in terms of specific examples, those skilled in the art will appreciate that many other configurations could be used. Accordingly, it will be appreciated that various equivalent modifications of the above-described embodiments may be made without departing from the spirit and scope of the invention.
