Power factor correction optimization by digital feedback

The disclosed exemplary embodiments relate generally to lighting systems, and more particularly to light emitting diode (LED) lighting systems.

LED lighting technology continues to advance resulting in improved efficiencies and lower costs. LED light sources are found in lighting applications ranging from small pin point sources to stadium lights. Low cost, good color rendition and high efficiency are factors driving the LED lamp market for general lighting. The use of a rectified line driver to power an LED lighting application allows for a small size and low cost power supply, however, due to the design of this type of supply, providing a high power factor generally results in low efficiency and vice versa. Furthermore, most supplies have fixed operating parameters. It would be advantageous to provide an LED lighting device that overcomes these and other problems.

As described herein, the exemplary embodiments overcome one or more of the above or other disadvantages known in the art.

The aspects of the disclosed embodiments are directed to a method of operating an LED lighting device including sampling a voltage of a rectified AC waveform used to provide power to the LED lighting device, selectively connecting one or more of a plurality of LED light sources in a one or more of a series and parallel combination to achieve a predetermined voltage across the connected LED light sources with respect to the sampled voltage, and regulating a current through the connected LED light sources to achieve a predetermined current with respect to the sampled voltage.

The method may include selectively connecting the one or more of a plurality of LED light sources in one or more of a series and parallel combination to achieve a predetermined efficiency as a ratio of the voltage across the connected LED light sources and the sampled voltage.

The method may also include regulating the current through the connected LED light sources to achieve a predetermined power factor as a ratio of the current through the connected LED light sources and the sampled voltage.

The method may further include connecting the one or more of the plurality of LED light sources in a first series and parallel combination while the sampled voltage remains within a first voltage range, and connecting the one or more of the plurality of LED light sources in a second series and parallel combination while the sampled voltage remains within a second voltage range.

The method may still further include identifying at least one of a plurality of voltage ranges into which the sampled voltage falls and connecting the one or more of the a plurality of LED light sources in a particular series and parallel combination while the sampled voltage remains within the identified voltage range.

The plurality of voltage ranges may include 0%-33%, 34%-50%, 51%-67%, 68%-84%, and 85%-100% of a peak voltage of the rectified AC waveform.

The aspects of the disclosed embodiments are also directed to an LED lighting device including a plurality of switches configured to selectively connect one or more of a plurality of LED light sources in one or more of a series and parallel combination, a linear regulator configured to control a current through the connected LED light sources, and a controller configured to sample a voltage of a rectified AC waveform used to provide power to the LED lighting device, control the plurality of switches to achieve a predetermined voltage across the connected LED light sources with respect to the sampled voltage, and control the linear regulator to achieve a predetermined current through the connected LED light sources with respect to the sampled voltage.

The controller may be configured to control the plurality of switches to selectively connect the one or more of a plurality of LED light sources in one or more of a series and parallel combination to achieve a predetermined efficiency as a ratio of the voltage across the connected LED light sources and the sampled voltage.

The controller may also be configured to control the linear regulator to achieve a predetermined power factor as a ratio of the current through the connected LED light sources and the sampled voltage.

The controller may further be configured to control the plurality of switches to connect the one or more of the plurality of LED light sources in a first series and parallel combination while the sampled voltage remains within a first voltage range, and to connect the one or more of the plurality of LED light sources in a second series and parallel combination while the sampled voltage remains within a second voltage range.

The controller may still further be configured to identify at least one of a plurality of voltage ranges into which the sampled voltage falls, and control the plurality of switches to connect the one or more of the plurality of LED light sources in a particular series and parallel combination while the sampled voltage remains within the identified voltage range.

The plurality of voltage ranges may include approximately 0%-33%, 34%-50%, 51%-67%, 68%-84%, and 85%-100% of a peak voltage of the rectified AC waveform.

These and other aspects and advantages of the exemplary embodiments will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the aspects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

FIG. 1 shows an exemplary circuit 100 according to the disclosed embodiments;

FIG. 2 shows different microcontroller operational states for selectively switching LED light sources; and

FIGS. 3-7 show different current paths resulting from different switch configurations according to the disclosed embodiments.

FIG. 1 shows an exemplary circuit 100 according to the disclosed embodiments. The circuit 100 at least includes a rectifier 105 , LED light sources LED 1 , LED 2 , and LED 3 , a diode D 1 , control switches Q 1 -Q 4 , current switches M 1 -M 5 , current sense resistors R 1 and R 2 , and a microcontroller IC 1 .

The circuit 100 operates to sample a voltage from the rectifier 105 and selectively connecting one or more of the LED light sources LED 1 , LED 2 , and LED 3 in a one or more of a series and parallel combination to achieve a predetermined voltage across the connected LED light sources with respect to the sampled voltage. The circuit 100 also operates to regulate a current through the connected LED light sources to achieve a predetermined current with respect to the sampled voltage.

Selectively connecting the LED light sources LED 1 , LED 2 , and LED 3 in different series and parallel combinations may achieve a predetermined efficiency as a ratio of the voltage across the connected LED light sources and the sampled voltage, and regulating the current through the connected LED light sources may achieve a predetermined power factor as a ratio of the current through the connected LED light sources and the sampled voltage. The current through the circuit 100 may be controlled to be, for example, a sine wave, square wave or other shaped current, may be controlled to match a voltage from the rectifier 105 within a certain range, or may be controlled to have any other suitable characteristics. In at least one embodiment, the current through the circuit 100 may be controlled to provide a particular power factor.

The rectifier 105 may be used to rectify power from an AC mains supply 110 and may be a half wave or full wave bridge rectifier with an output that extends from 0v to approximately 1V below the peak output voltage of the AC mains supply. While a full wave bridge rectifier is shown, the disclosed embodiments may utilize any suitable rectification circuitry.

The LED light sources LED 1 , LED 2 , LED 3 may include one or more LED chips or packaged LED's connected in various configurations to achieve a particular voltage rating and optionally one or more of a color temperature, color rendering index, lumen output, beam angle or other characteristic. In some embodiments, LED light source LED 1 may have a 36V rating, while LED light sources LED 2 and LED 3 may each have a 72V rating.

Diode D 1 may be any suitable diode having sufficient current carrying capability to provide a current path between LED light source LED 2 and LED light source LED 3 .

Control switches Q 1 -Q 4 may include any semiconductor devices suitable for receiving a digital switching signal from the microcontroller IC 1 and providing enough power to drive current switches M 2 -M 5 . For example, control switches Q 1 -Q 4 may be bipolar junction transistors, field effect transistors, or any other suitable switching devices.

Current switches M 2 -M 5 may be any switching devices having sufficient current carrying capability to provide current paths among and around the LED light sources LED 1 , LED 2 , LED 3 and for switching the LED light sources LED 1 , LED 2 , LED 3 in different serial and parallel combinations. In at least one embodiment, current switches M 2 -M 5 be P-channel power MOSFETs.

Current switch M 1 may be any switching device capable of controlling the current through the circuit 100 under control of the microcontroller IC 1 . In some exemplary embodiments, current switch M 1 may be an N-channel power MOS transistor.

Microcontroller IC 1 receives power from power signals VDD and VSS and generally includes computer readable program code 115 stored on at least one computer readable medium for carrying out and executing the process steps described herein. The computer readable medium may be a memory 120 of the microcontroller IC 1 . In alternate aspects, the computer readable program code may be stored in a memory external to, or remote from, microcontroller IC 1 , and the memory 120 may include any media which is readable and executable by a computer. The microcontroller 115 may also include a processor 125 for executing the computer readable program code 115 . In at least one aspect, the microcontroller IC 1 may include one or more input or output devices, including sensing circuitry 130 for determining a voltage at inputs RC 0 and RC 1 and driver circuitry 135 for providing signals RC 2 -RC 5 and RA 5 to drive current switch M 1 and control switches Q 1 -Q 4 .

Sensing circuitry 130 may include one or more A/D converters utilized to measure signal RC 0 representative of the voltage from rectifier 105 . The one or more A/D converters may also be utilized to measure the voltage of signal RC 1 representing a current through circuit 100 . The sensing circuitry 130 may also include one or more operational amplifiers to provide control signals 140 to driver circuitry 135 for controlling output RC 2 which operates as a gate drive signal to M 1 . The microcontroller IC 1 may operate the sensing circuitry 130 and the driver circuitry 135 to provide closed loop control of M 1 and the current through circuit 100 under the control of program code 115 , for example, operating M 1 as a linear regulator. In some embodiments, the microcontroller IC 1 , under the control of program code 115 , may operate the sensing circuitry 130 and the driver circuitry 135 to provide closed loop control of M 1 and the current through circuit 100 based on the voltage from the rectifier 105 represented by signal RC 0 . As a result, the current through the circuit 100 may be controlled to provide one or more of a particular wave form, wave shape, or power factor.

Furthermore, the microcontroller IC 1 , under the control of program code 115 , may operate the sensing circuitry 130 to measure signal RC 0 , representing the voltage from the rectifier 105 , and selectively switch the LED light sources LED 1 , LED 2 , LED 3 in and out of the circuit 100 in different combinations as the voltage from the rectifier 105 changes. Thus, at each different voltage level, a combination of the LED light sources LED 1 , LED 2 , LED 3 corresponding to the voltage level are connected into circuit 100 in order to efficiently use the voltage to produce light. For example, as the voltage from the rectifier approaches 36V, LED light source LED 1 having a 36V rating may be switched into circuit 100 . As another example, as the voltage from the rectifier approaches 144V, LED light sources LED 2 and LED 3 each having a 72V rating may be switched into circuit 100 in series.

Turning to FIG. 2 , the microcontroller may operate in different exemplary states to selectively switch the LED light sources LED 1 , LED 2 , LED 3 in and out of the circuit 100 in different combinations, resulting in different current flows through circuit 100 as shown in FIGS. 3-7 . While the different states, State 1, State 2, State 3, State 4, and State 5 are described with respect to various voltage ranges, it should be understood that the voltage ranges are exemplary and non-limiting and that the disclosed embodiments may operate across any suitable voltage ranges. It should be noted that in the description of States 1-5, the voltage ratings of LED light sources LED 1 , LED 2 , LED 3 of 36V, 72V, and 72V, respectively, are also exemplary and non-limiting. It should also be noted that in some embodiments, as the microcontroller IC 1 operates through the different states, the microcontroller IC 1 may continuously operate to control M 1 and the current through circuit 100 . By using the microcontroller IC 1 to simultaneously control the LED light source configuration and the current flow, the circuit 100 may provide a range of efficient power usage and power factors.

The microcontroller IC 1 operates to turn signals RC 2 -RC 5 and RA 5 on and off under control of program code 115 . For purposes of the disclosed embodiments, an “on” signal is active and provides a driving voltage or current to the connected control or current switch. Correspondingly, an “off” signal is inactive and does not provide a driving voltage or current to the connected control switch or current switch.

In State 1, as the voltage of signal RC 0 increases from 0-60V, signal RC 5 is off causing Q 3 and M 4 to be non-conducting, signal RA 5 is off causing Q 4 and M 5 to be non-conducting, signal RC 3 is off causing Q 1 and M 2 to be non-conducting, and signal RC 4 is on, causing Q 2 and M 3 to be on and conducting, turning LED 1 on, and bypassing or shorting LED 2 and LED 3 . As a result, current flows from the positive side of the rectifier through LED 1 and through M 1 , as shown in FIG. 3 . In State 2, as the voltage increases from 60-90V, signal RC 5 is on causing Q 3 and M 4 to be conducting and signal RA 5 is on causing Q 4 and M 5 to be conducting, coupling LED 2 and LED 3 in parallel. Signal RC 3 is on causing Q 1 and M 2 to be conducting and shorting LED 1 . Signal RC 4 is off, causing Q 2 and M 3 to be off and non-conducting. As a result current flows from the positive side of the rectifier through LED 2 and LED 3 in parallel and through M 1 , as shown in FIG. 4 .

In State 3, as the voltage continues to increase from 90-120V, signal RC 5 is on causing Q 3 and M 4 to be conducting and signal RA 5 is on causing Q 4 and M 5 to be conducting, coupling LED 2 and LED 3 in parallel. Signal RC 3 is off causing Q 1 and M 2 to be non-conducting and causing current to flow through LED 1 . Signal RC 4 is off, causing Q 2 and M 3 to be off and non-conducting. As a result current flows from the positive side of the rectifier through LED 1 and through LED 2 and LED 3 in parallel and through M 1 , as shown in FIG. 5 .

In State 4, as the voltage continues to increase from 120-150V, signal RC 5 is off causing Q 3 and M 4 to be non-conducting and signal RA 5 is off causing Q 4 and M 5 to be non-conducting, coupling LED 2 and LED 3 in series through diode D 1 . Signal RC 3 is on causing Q 1 and M 2 to be conducting and causing current to flow around LED 1 . Signal RC 4 is off, causing Q 2 and M 3 to be off and non-conducting. As a result current flows from the positive side of the rectifier through LED 2 and LED 3 in series and through M 1 , as shown in FIG. 6 .

In State 5, as the voltage increases to over 150V, signal RC 5 is off causing Q 3 and M 4 to be non-conducting and signal RA 5 is off causing Q 4 and M 5 to be non-conducting, coupling LED 2 and LED 3 in series through diode D 1 . Signal RC 3 is off causing Q 1 and M 2 to be non-conducting and causing current to flow through LED 1 . Signal RC 4 is off, causing Q 2 and M 3 to be off and non-conducting. As a result current flows from the positive side of the rectifier through LED 1 , LED 2 and LED 3 in series and through M 1 , as shown in FIG. 7 .

Thus, turning current switches M 2 -M 5 on and off at various voltage levels may provide different efficiencies, and by controlling the current through circuit 100 , a particular power factor may be achieved. By utilizing the microcontroller IC 4 , both of these functions may be optimized to achieve a desired power factor without more than desired efficiency losses.

Various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, all such and similar modifications of the teachings of the disclosed embodiments will still fall within the scope of the disclosed embodiments.

Various features of the different embodiments described herein are interchangeable, one with the other. The various described features, as well as any known equivalents can be mixed and matched to construct additional embodiments and techniques in accordance with the principles of this disclosure.

Furthermore, some of the features of the exemplary embodiments could be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the disclosed embodiments and not in limitation thereof.