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Researchers Submit Patent Application, "Electronic Control Gears for Led Light Engine and Application Thereof", for Approval

August 22, 2014



By a News Reporter-Staff News Editor at Energy Weekly News -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Yu, Ching Sheng (New Taipei City, TW); Wang, Chih Liang (Keelung City, TW); Chen, Kuang Hui (New Taipei City, TW), filed on January 26, 2014, was made available online on August 7, 2014.

The patent's assignee is Groups Tech Co., Ltd.

News editors obtained the following quote from the background information supplied by the inventors: "The invention relates to electronic control gears for LED (light emitting diode) light engine. In particular, the electronic control gears for LED light engine use the normally closed electronic switches to gear up or down the number and current of excited LEDs in the LED array segments in accordance with the level of the AC input voltage in order to improve the power factor. Furthermore, valley fillers and/or dummy loads can be optionally added in to improve the flicker phenomenon and/or decrease the total harmonic distortion, respectively.

"As compared with the traditional lighting devices, the LED has a higher luminous efficacy. The LEDs can give off more than 100 lumens per watt because less electric energy is converted into waste heat. In sharp contrast, a traditional bulb only gives off about 15 lumens per watt because more electric energy is converted into waste heat. Moreover, LED-based lighting devices are gradually becoming the preferred lighting equipment because of having a relatively longer life to reduce maintaining cost, being less susceptible to exterior interference, and being less likely to get damaged.

"Technically, LEDs need to be DC-driven. So, an AC sinusoidal voltage source would normally be rectified by a full-wave or half-wave rectifier into a rectified sinusoidal voltage source before coming into use. In the vicinity of the beginning and end of each DC pulse cycle (aka 'dead time') where the input voltage is lower than the total forward voltage drop of the LEDs, the LEDs cannot be forward-biased to light up. The dead time is the partial period during which the LED current ceases conduction while the conduction angle is the partial period during which the circuit conducts the LED current. The dead time in union with the conduction angle constitutes a full period of the rectified sinusoidal voltage pulse. A longer dead time translates to a smaller conduction angle, and hence a lower power factor; more specifically, the longer the dead time, the smaller the conduction angle, and the lower the power factor, because the line current is getting too thin to be similar in shape to the line voltage. Traditional LED drivers usually come along with three application problems.

"The first problem would be the need for a more complicated and more expensive driving circuit consisting of a filter, a rectifier, and a power factor corrector (PFC), etc. to drive LEDs. Besides, the short-life electrolytic capacitor used as an energy-storage component in the PFC is the key reason accounting for the shortened overall lifespan of the whole LED illumination apparatus, cancelling out the virtues of LED lighting.

"The second problem would be the flicker phenomenon due to no current flowing through the LEDs during the dead time. The LEDs would immediately light up with a positive driving current, and go out with a zero driving current, causing the LEDs to flicker if there exists a dead time. If a typical AC sinusoidal frequency is 60 Hz, the rectified sinusoidal frequency will double as 120 Hz. The flicker phenomenon indeed takes place during the dead time at a repetition rate of twice the AC sinusoidal frequency although its existence might hardly be perceived by human eyes.

"The third problem would be a relatively lower power factor exhibited by a low-power PFC with a loop current too weak to be precisely sensed to correctly shape the AC input current into a sinusoidal waveform. The power factor (PF) can be calculated as the input power divided by the product of the input voltage (line voltage) and the input current (line current), i.e. PF=P/(V.times.I), wherein P is the input power, and V and I are respectively the root-mean-square values of the line voltage and the line current. The power factor is used to measure the electricity utilization. The more similar the line current is to the line voltage, the better the electricity utilization and the higher the power factor. When the line current and the line voltage are consistent in terms of identical phase and identical shape, the power factor would reach 1 (the maximum value). The conventional PFC needs to sense its loop current for the purpose of aligning the line current with the line voltage. If the loop current goes too low to be precisely sensed by the current sense circuitry in the PFC stage, the PFC would fail to properly keep the line current in phase and in shape with the line voltage to achieve a high power factor. Often mentioned in the same breath with the issue of a low PF is the issue of a high total harmonic distortion (THD). According to the theory of Fourier series expansion of any periodic signal, any discontinuous or jumping points in the periodic waveform would incur higher-order harmonics on top of the fundamental component, causing the THD to increase. The THD resulting from the discontinuous or jumping points in the AC input current waveform would have much to do with the existence of the dead time.

"Simplifying the electronic circuit, reducing the manufacturing and maintaining costs, eliminating the flicker phenomenon, as well as improving the power factor still remain the main topics put at the top of the agenda when it comes to developing new LED lighting apparatuses. The invention proposed herein to address the above issues provides an LED light engine, allowable to directly operate off of an AC power supply, in an attempt to get many benefits such as low cost, high performance, long lifespan, simple circuit topology, low flicker phenomenon, and high power factor."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "The invention embodiments provide electronic control gears for LED light engine. Along the rising edge of the rectified sinusoidal input voltage, the electronic control gears for LED light engine successively light up the LED array segments; along the falling edge of the rectified sinusoidal input voltage, the electronic control gears for LED light engine successively put out the LED array segments. The invention embodiments have benefits of simplifying the electronic circuits, improving the luminous efficacy and power factor, as well as reducing the manufacturing and maintaining costs, etc. The electronic control gears for LED light engine provided by the invention embodiments are essentially equipped with a rectifier (such as a full-wave or half-wave rectifier) for AC-to-DC conversion.

"An optional valley filler, connected to the two DC output terminals of the rectifier and in parallel with the LED light engine, fills up the LED current valleys with a preset constant current only during the dead time to improve the flicker phenomenon.

"An optional dummy load, connected to the two DC output terminals of the rectifier and in parallel with the LED light engine, draws a line current only during the dead time to decrease the total harmonic distortion by eliminating the discontinuous or jumping points.

"The electronic control gears for LED light engine provided by the invention embodiments comprise a switch regulator chain connected in parallel with an LED array chain. The LED array chain comprises a plurality of LED array segments connected in series. The switch regulator chain comprises a plurality of switch regulators connected in series. Each switch regulator is connected in parallel with a corresponding LED array segment, except for the lowest segment of the LED array chain.

"Each switch regulator comprises a bypass switch and a detector. The bypass switch is implemented with a normally closed electronic switch, acting like a short circuit with an adequate nonnegative gate-source voltage (0.ltoreq.V.sub.GS

"The detector can take on any type of a current detector, a voltage detector, an optical detector, a magnetic detector, or a comparator, wherein the current or voltage detector would be the preferred choice.

"During the first half of the period, the rectified sinusoidal input voltage goes up to its peak from its zero. When the rising input voltage is still insufficient to forward-bias the lower LED array segment connected to the bottom of the present bypass switch, the present detector receives a below-threshold voltage/current sense signal, and the present bypass switch remains in its ON state to short out the present LED array segment connected in parallel with it. When the rising input voltage has been high enough to forward-bias the lower LED array segment connected to the bottom of the present bypass switch, the present detector receives a jittering voltage/current sense signal, and the present bypass switch regulates the LED current of the lower LED array segment subsequent to it at a preset constant level. When the rising input voltage has been high enough to forward-bias the present LED array segment connected in parallel with the present bypass switch, the present detector receives an at-threshold voltage/current sense signal, and the present bypass switch is shut off because of a higher current level regulated by the higher bypass switch connected to the top of it. In this way, the electronic control gear lights up each segment in the LED array segments from the bottom up.

"During the second half of the period, the rectified sinusoidal input voltage goes down to its zero from its peak. When the falling input voltage is still high enough to forward-bias the present LED array segment connected in parallel with the present bypass switch, the present detector receives an at-threshold voltage/current sense signal, and the present bypass switch is shut off because of a higher current level regulated by the higher bypass switch connected to the top of it. When the falling input voltage is still high enough to forward-bias the lower LED array segment connected to the bottom of the present bypass switch, the present detector receives a jittering voltage/current sense signal, and the present bypass switch regulates the LED current of the lower LED array segment subsequent to it at a preset constant level. When the falling input voltage has been insufficient to forward-bias the lower LED array segment connected to the bottom of the present bypass switch, the present detector receives a below-threshold voltage/current sense signal, and the present bypass switch switches back to its ON state to short out the present LED array segment connected in parallel with it. In this way, the electronic control gear puts out each segment in the LED array segments from the top down.

"The valley filler provided by the invention embodiments comprises a programmable constant current source and at least one energy storage capacitor. The programmable constant current source is used to charge the energy storage capacitor with a preset constant current to make the capacitor voltage fit for valley filling.

"When the input voltage is higher than the energy storage capacitor voltage, the energy storage capacitor is charged with a first preset constant current for the capacitor voltage to reach an intermediate voltage level between V.sub.f1 and V.sub.f1+V.sub.f2, where V.sub.f1 and V.sub.f2 stand for the forward voltage drop of the lowest and the second lowest LED array segments in the LED arrays, respectively. When the input voltage is lower than the energy storage capacitor voltage, the energy storage capacitor is discharged with a second preset constant current to light up the lowest LED array segment only during the dead time to improve the flicker phenomenon.

"The dummy load provided by the invention embodiment comprises a controlled switch and a resistive load. The controlled switch electrically couples the resistive load to the two DC output terminals of the rectifier only within the dead time, and then cuts off the resistive load. The resistive load draws a line current only during the dead time to decrease the total harmonic distortion by means of stuffing up the dead time in the line current waveform for eliminating the discontinuous or jumping points.

"Only during the dead time, the controlled switch is turned on to connect the resistive load to the two DC output terminals of the rectifier. Elsewhere, the controlled switch is shut off to disconnect the resistive load from the two DC output terminals of the rectifier. Therefore, the dummy load can effectively help decrease the total harmonic distortion with no significant loss of power efficiency due to resistive consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

"The foregoing conceptions and their accompanying advantages of this invention will become more readily appreciated after being better understood by referring to the following detailed description, in conjunction with the accompanying drawings.

"FIG. 1 illustrates a superordinate main circuit structure of the electronic control gears for LED light engine according to the embodiment of the invention. The electronic control gears for LED light engine comprise a switch regulator chain with a plurality of switch regulators connected in series. The switch regulator chain is connected in parallel with the LED array segments chain. Each switch regulator is connected in parallel with a corresponding LED array segment, except for the last segment of the LED array segments. The switch regulator comprises a bypass switch and a detector, wherein the bypass switch transits around three functional states: ON state, regulating state, and OFF state, depending on the signal sensing of the detector.

"FIG. 2A illustrates the divide-and-conquer strategy for lighting up or putting out the LED array segments according to the embodiment of the invention. During the first half of the period, the gradually rising sinusoidal input voltage lights up each segment from the bottom up. During the second half of the period, the gradually falling sinusoidal input voltage puts out each segment from the top down.

"FIG. 2B illustrates the line current waveform corresponding to the divide-and-conquer strategy illustrated in FIG. 2A. During the first half of the period, each segment is lit up along the trajectory of a step-up waveform. During the second half of the period, each segment is put out along the trajectory of a step-down waveform. The quasi-sinusoidal line current closely follows the sinusoidal line voltage, so the power factor can be effectively improved to reach a very high level.

"FIG. 3 reveals the LED lighting equipment having the electronic control gears for LED light engine according to the embodiment of the invention, where an n-channel depletion-mode MOSFET (depletion n-MOSFET) is used as the bypass switch, a voltage divider is used as the detector, and the present detector detects the partial or full forward voltage drop of the lower LED array segment to control the operating modes of the present bypass switch.

"FIG. 4 reveals the LED lighting equipment having the electronic control gears for LED light engine according to the embodiment of the invention, where an n-channel depletion-mode MOSFET is used as the bypass switch, and a shunt regulator is used as a current detector to control the operating modes of the n-channel depletion-mode MOSFET.

"FIG. 5 reveals the LED lighting equipment having the electronic control gears for LED light engine according to the embodiment of the invention, where an n-channel depletion-mode MOSFET is used as the bypass switch, and an npn bipolar junction transistor (BJT) is used as a current detector to control the operating modes of the n-channel depletion-mode MOSFET.

"FIG. 6A unveils the LED lighting equipment with an optional double-capacitor valley filler according to the embodiment of the invention, wherein the double-capacitor valley filler is connected to the two DC output terminals of the rectifier and in parallel with the LED light engine to further address the thorny problem with LED flicker phenomenon. The double-capacitor valley filler comprises two energy storage capacitors and a programmable constant current source. The programmable constant current source comprises a MOSFET, a diode and a BJT. When the input voltage is higher than the energy storage capacitor voltage, the energy storage capacitor is charged with a first preset constant current for the capacitor voltage to reach a voltage level suitable for valley filling. When the input voltage is lower than the energy storage capacitor voltage, the energy storage capacitor is discharged with a second preset constant current to light up the lowest LED array segment only during the dead time to improve the flicker phenomenon. The feature of this embodiment would be: the two energy storage capacitors get charged in series in the time of a higher input voltage and discharged in parallel in the time of a lower input voltage.

"FIG. 6B unveils the LED lighting equipment with an optional, simplified double-capacitor valley filler according to the embodiment of the invention, wherein the simplified double-capacitor valley filler, resulting from eliminating the three diodes shown in FIG. 6A, has a different feature: the two energy storage capacitors get charged in series in the time of a higher input voltage and discharged in series in the time of a lower input voltage.

"FIGS. 6C and 6D unveil two LED lighting equipments with two optional, further simplified single-capacitor valley fillers according to the embodiment of the invention, wherein the two further simplified single-capacitor valley fillers result from eliminating either of the two energy storage capacitors shown in FIG. 6B to form up two single-capacitor valley fillers.

"FIGS. 7A and 7B shed light upon the effect of the valley filler on the LED current waveform. FIG. 7A illustrates the consistency between the LED current and the line current before the adoption of a valley filler. That is to say, both the LED current and the line current remain zero during the dead time with an indication of the flicker phenomenon. FIG. 7B illustrates the difference between the LED current and the line current after the adoption of a valley filler. The LED current valleys get filled up with a second preset constant current only during the dead time to improve the flicker phenomenon while the line current still stays zero because the reverse-biased rectifier blocks the road when the capacitor voltage is higher than the input voltage. The dead time in the line current also increases because the capacitor voltage has to be charged up to a voltage level higher than the forward voltage drop of the lowest LED array segment.

"FIG. 8 illustrates the LED lighting equipment with an optional dummy load according to the embodiment of the invention, wherein the dummy load is connected to the two DC output terminals of the rectifier and in parallel with the LED light engine to further fix the issue with a high total harmonic distortion. The dummy load comprises a controlled switch and a resistive load. The controlled switch electrically connects the resistive load to the two DC output terminals of the rectifier only within the dead time, and then casts aside the resistive load. The resistive load draws a line current only during the dead time to decrease the total harmonic distortion by eliminating the discontinuous or jumping points. Therefore, the dummy load can effectively help decrease the total harmonic distortion with no significant loss of power efficiency due to resistive consumption.

"FIGS. 9A and 9B shed light upon the effect of the dummy load on the line current waveform. FIG. 9A illustrates discontinuous or jumping points due to a dead time before the adoption of a dummy load while FIG. 9B illustrates no discontinuous or jumping points due to no dead time after the adoption of a dummy load. The total harmonic distortion can be effectively decreased by eliminating discontinuous or jumping points from the line current with the use of a dummy load, drawing a line current only within the dead time."

For additional information on this patent application, see: Yu, Ching Sheng; Wang, Chih Liang; Chen, Kuang Hui. Electronic Control Gears for Led Light Engine and Application Thereof. Filed January 26, 2014 and posted August 7, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=5321&p=107&f=G&l=50&d=PG01&S1=20140731.PD.&OS=PD/20140731&RS=PD/20140731

Keywords for this news article include: Electric Energy, Groups Tech Co. Ltd.

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Source: Energy Weekly News


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