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Researchers Submit Patent Application, "Pfc Led Driver Capable of Reducing Current Ripple", for Approval

March 5, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventor Wang, Yen-Hui (Tiapei City, TW), filed on August 8, 2012, was made available online on February 20, 2014.

No assignee for this patent application has been made.

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to a PFC (power factor correction) LED (light emitting diode) driver, especially to a PFC LED driver capable of reducing current ripple.

"For general linear LED drivers, inferior efficiencies are their major disadvantages. Common solutions for improving efficiencies are to divide a string of LEDs into several sections, and select one section or multiple sections thereof to act as a load according to the voltage of a full-wave rectified line input voltage.

"FIG. 1 illustrates a circuit diagram of a prior art PFC LED driver. As illustrated in FIG. 1, the prior art PFC LED driver includes an amplifier 110, resistors 111-113, an NMOS transistor 114, LED modules 120, 130, and 140, and switches 121, 131, and 141.

"The amplifier 110 has a positive input coupled to a control voltage V.sub.C, a negative input coupled to the resistor 113, and an output coupled to the NMOS (n type metal oxide semiconductor) transistor 114.

"The resistors 111 and 112 are used to divide a full-wave rectified line input voltage V.sub.IN to generate the control voltage V.sub.C.

"The resistor 113 is used to convert an output current I.sub.O into a voltage.

"The NMOS transistor 114 is used to provide a high output impedance for the output current I.sub.O.

"The LED module 120 and the switch 121 form a first parallel combination, the LED module 130 and the switch 131 form a second parallel combination, the LED module 140 and the switch 141 form a third parallel combination, and the first parallel combination, the second parallel combination, and the third parallel combination are connected in series.

"When in operation, the voltage at the negative input of the amplifier 110 will follow the control voltage V.sub.C due to a negative feedback mechanism of this circuit, and the output current I.sub.O will thereby follow the full-wave rectified line input voltage V. Besides, switch control signals S.sub.1, S.sub.2, S.sub.3 will switch the switches 121, 131, 141 according to the voltage of the full-wave rectified line input voltage V.sub.IN, to select a corresponding LED module or corresponding LED modules from the LED modules 120, 130, 140 to serve as a load for the LED driver, so as to improve the power efficiency. For example, the LED module 120 can be selected as the load with the switch 121 being turned off and the switches 131, 141 being turned on when the full-wave rectified line input voltage V.sub.IN is under a first threshold; the LED module 120 and the LED module 130 can be selected to form the load with the switches 121, 131 being turned off and the switch 141 being turned on when the full-wave rectified line input voltage V.sub.IN is above the first threshold and under a second threshold; and the LED module 120, the LED module 130, and the LED module 140 can be selected to form the load with the switches 121, 131, 141 being turned off when the full-wave rectified line input voltage V.sub.IN is above the second threshold.

"FIG. 2 illustrates a circuit diagram of another prior art PFC LED driver. As illustrated in FIG. 2, the prior art PFC LED driver includes an amplifier 210, resistors 211-213, an NMOS transistor 214, LED modules 220, 230, and 240, and switches 231, 241.

"The amplifier 210 has a positive input coupled to a control voltage V.sub.C, a negative input coupled to the resistor 213, and an output coupled to the NMOS transistor 214.

"The resistors 211 and 212 are used to divide a full-wave rectified line input voltage V.sub.IN to generate the control voltage V.sub.C.

"The resistor 213 is used to convert an output current I.sub.O into a voltage.

"The NMOS transistor 214 is used to provide a high output impedance for the output current I.sub.O.

"The LED module 220 and the switch 221 form a first parallel combination. The LED module 230 forms a first series combination with the first parallel combination. The switch 231 forms a second parallel combination with the first series combination. The LED module 240 forms a second series combination with the second parallel combination.

"When in operation, the voltage at the negative input of the amplifier 210 will follow the control voltage V.sub.C due to a negative feedback mechanism of this circuit, and the output current I.sub.O will thereby follow the full-wave rectified line input voltage V.sub.IN. Besides, switch control signals S.sub.4, S.sub.5 will switch the switches 221, 231 according to the voltage of the full-wave rectified line input voltage V.sub.IN, to select a corresponding LED module or corresponding LED modules from the LED modules 220, 230, 240 to serve as a load for the LED driver, and thereby improve the power efficiency. For example, the LED module 240 can be selected as the load with the switches 221, 231 being turned on when the full-wave rectified line input voltage V.sub.IN is under a first threshold; the LED module 230 and the LED module 240 can be selected to form the load with the switches 221 being turned on and the switch 231 being turned off when the full-wave rectified line input voltage V.sub.IN is above the first threshold and under a second threshold; and the LED module 220, the LED module 230, and the LED module 240 can be selected to form the load with the switches 221, 231 being turned off when the full-wave rectified line input voltage V.sub.IN is above the second threshold.

"Please refer to FIG. 3, which illustrates corresponding waveforms of the full-wave rectified line input voltage V.sub.IN and the output current I.sub.O of the circuits in FIG. 1 and FIG. 2. As illustrated in FIG. 3, the output current I.sub.O has an average of I.sub.AVG and varies proportional to the full-wave rectified line input voltage V.sub.IN most of the time to result in a good power factor.

"However, although the electrical power efficiency is improved, the luminous Efficiency--the ratio of luminous flux to electrical power--is substantially degraded due to a fact that, the LED currents in FIG. 1 and FIG. 2 are generated to have waveforms analog to the waveform of the full-wave rectified line input voltage to meet a high PFC requirement, and thereby has a large ripple. For LEDs, large current ripples are adverse to luminous efficiency and can cause a flicker phenomenon that is uncomfortable to human eyes. To have a good luminous efficiency and eliminate the flicker phenomenon, the waveform of the LED current is expected to be as close to a DC line as possible, but with the LED current close to a DC line, the power factor can be greatly compromised.

"To solve the foregoing tangled problems, a novel PFC LED driver is therefore needed."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "One objective of the present invention is to disclose a PFC LED driver capable of reducing the current ripple of LEDs to improve the luminous efficiency without compromising the power factor.

"Another objective of the present invention is to disclose a PFC LED driver capable of reducing the current ripple of LEDs without compromising the electrical power efficiency.

"Still another objective of the present invention is to disclose a PFC LED driver capable of reducing the current ripple of LEDs to prevent a flicker phenomenon.

"To attain the foregoing objectives, a PFC LED driver capable of reducing current ripple is proposed, including: a current source unit, having a control terminal, a first channel terminal, and a second channel terminal, the control terminal being coupled to a control voltage, which is a ratio of a full-wave rectified line input voltage, the first channel terminal being coupled to a power line, and the second channel terminal being used to generate an output current according to the control voltage; and at least one LED load unit, being in series with the current source unit, wherein each of the at least one LED load unit includes: a first load, including a first parallel combination of an LED module and a capacitor, wherein the LED module has at least one light emitting diode; a diode, being in a first series combination with the first load; and a switch, being in a second parallel combination with the first series combination.

"In one embodiment, the power line is a ground.

"In one embodiment, the power line is the full-wave rectified line input voltage.

"In one embodiment, the PFC LED driver capable of reducing current ripple further includes a voltage divider, which is coupled between the full-wave rectified line input voltage and a ground for generating the control voltage.

"In one embodiment, the voltage divider includes two resistors connected in series.

"To attain the foregoing objectives, another PFC LED driver capable of reducing current ripple is proposed, including: a current source unit, having a control terminal, a first channel terminal, and a second channel terminal, the control terminal being coupled to a control voltage, which is a ratio of a full-wave rectified line input voltage, the first channel terminal being coupled to a power line, and the second channel terminal being used to generate an output current according to the control voltage; and an LED load unit, being in series with the current source unit, wherein the LED load unit includes: a first load, including a first parallel combination of a first LED module and a first capacitor, wherein the first LED module has at least one light emitting diode; a first diode, being in a first series combination with the first load; a first switch, being in a second parallel combination with the first series combination; a second load, including a third parallel combination of a second LED module and a second capacitor, wherein the LED module has at least one light emitting diode; a second diode, being in a second series combination with the second load and the second parallel combination; and a second switch, being in a fourth parallel combination with the second series combination.

"In one embodiment, the power line is a ground.

"In one embodiment, the power line is the full-wave rectified line input voltage.

"In one embodiment, the PFC LED driver capable of reducing current ripple further includes a voltage divider, which is coupled between the full-wave rectified line input voltage and a ground for generating the control voltage.

"In one embodiment, the voltage divider includes two resistors connected in series.

"To make it easier for our examiner to understand the objective of the invention, its structure, innovative features, and performance, we use preferred embodiments together with the accompanying drawings for the detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 illustrates a circuit diagram of a prior art PFC LED driver.

"FIG. 2 illustrates a circuit diagram of another prior art PFC LED driver.

"FIG. 3 illustrates corresponding waveforms of the full-wave rectified line input voltage V.sub.IN and the output current I.sub.O of the circuits in FIG. 1 and FIG. 2.

"FIG. 4 illustrates a circuit diagram of a PFC LED driver capable of reducing current ripple according to a preferred embodiment of the present invention.

"FIG. 5a illustrates a scenario where a switch is turned on and the charge on a capacitor is protected by a reversely biased diode from being discharged by the switch.

"FIG. 5b illustrates a scenario where the capacitor of FIG. 5a contributes a current I.sub.A to an LED module when the diode of FIG. 5a is off.

"FIG. 6 illustrates a circuit diagram of a PFC LED driver capable of reducing current ripple according to another preferred embodiment of the present invention.

"FIG. 7 illustrates a PFC LED driver capable of reducing current ripple according to still another preferred embodiment of the present invention.

"FIG. 8 illustrates a circuit diagram of a PFC LED driver capable of reducing current ripple according to still another preferred embodiment of the present invention."

For additional information on this patent application, see: Wang, Yen-Hui. Pfc Led Driver Capable of Reducing Current Ripple. Filed August 8, 2012 and posted February 20, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4687&p=94&f=G&l=50&d=PG01&S1=20140213.PD.&OS=PD/20140213&RS=PD/20140213

Keywords for this news article include: Patents, Electronics, Light-emitting Diode.

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Source: Electronics Newsweekly


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