EP1814365A1 - LED driving device with pulse width modulation - Google Patents
LED driving device with pulse width modulation Download PDFInfo
- Publication number
- EP1814365A1 EP1814365A1 EP06005074A EP06005074A EP1814365A1 EP 1814365 A1 EP1814365 A1 EP 1814365A1 EP 06005074 A EP06005074 A EP 06005074A EP 06005074 A EP06005074 A EP 06005074A EP 1814365 A1 EP1814365 A1 EP 1814365A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- cycle
- pwm
- clocks
- sub
- cycles
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
- G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
- G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/20—Controlling the colour of the light
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/32—Pulse-control circuits
- H05B45/325—Pulse-width modulation [PWM]
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/02—Improving the quality of display appearance
- G09G2320/0247—Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/2007—Display of intermediate tones
- G09G3/2018—Display of intermediate tones by time modulation using two or more time intervals
Definitions
- the present invention relates to a LED driving device with pulse width modulation (PWM).
- PWM pulse width modulation
- brightness of an LED can be varied with the duty cycle of a control signal delivered from a driving IC (integrated circuit) device.
- a driving IC integrated circuit
- an external control system will output a signal with longer continuous "OFF" to the driving IC device, so that the LED is not lit or lasts unilluminated for a longer time. In such situation, the LED display will flicker and show poor quality as it's apparently visible for viewers.
- FIG 1 compares the images without and with flickering.
- the present invention provides a solution by dividing a continuous "ON" signal into many discrete “ON” signals and distributing them uniformly.
- the LED driving device with PWM primarily comprises a PWM unit and LED driving circuits.
- the LED driving device receives a preset value about brightness of the LED and delivers the preset value to the PWM unit.
- the PWM unit generates an ON/OFF signal with a duty cycle in a PWM cycle corresponding to the preset value and then modulates the ON/OFF signal.
- the modulated signal is output to the LED through the LED driving circuit to perform desired brightness.
- the PWM unit modulates the ON/OFF signal from one signal of higher gray-scale resolution to two or more signals of relatively lower gray-scale resolution, so that the LED will be lit more frequently with a higher refresh rate and brightness of the LED before and after modulation is exactly the same or similar to a viewer.
- the duty cycle of the ON/OFF signal is preserved before and after modulation.
- the PWM cycle of the ON/OFF signal has a continuous "ON" duration composed of a major "ON” cycle and a minor “ON” cycle.
- the PWM unit modulates the ON/OFF signal by dividing the major "ON” cycle into two or more parts each defined as a major "ON” sub-cycle, and distributing the major "ON" sub-cycles in the PWM cycle according to an algorithm.
- the minor "ON” cycle may be ignored or further divided by the PWM unit into two or more parts each defined as a minor "ON" sub-cycle all of which are then distributed with the major "ON" sub-cycles.
- the major "ON” cycle is evenly divided and uniformly distributed.
- the modulated signal output from the PWM unit is normally clock-based.
- variables n, m, k, M, A, B, i are defined as follows:
- each of the sub-cycles having (2 m -1) ⁇ 2 k clocks may comprise A ⁇ 2 k clocks for "ON", and one sub-cycle having 2 k ⁇ 2 n-m-k clocks may comprise B clocks for "ON”.
- each of the sub-cycles having 2 m ⁇ 2 k clocks may comprise (A ⁇ 2 k + i ) clocks for "ON".
- the LED display can exhibit an image with desired brightness and without flickering as the duty cycle is preserved and the refresh rate is increased. Also note that specific limitation to n or M is not necessary and depends on developments of photo-electric technologies.
- Diagram (a) indicates 16 reference clocks.
- Diagram (b) indicates an undivided PWM cycle composed of nine continuous "ON” clocks and seven continuous “OFF” clocks. That is, the duty cycle is 9/16.
- Examples (A) and (B) explain processes for refresh rates 4 and 2, respectively.
- the diagram (d) shows a result of the diagram (a) processed with a frequency division factor 2, and each clock of the diagram (d) is defined as a bi-clock.
- Formula (II) is then employed to divide the nine "ON" clocks.
- each sub-cycle is composed of two continuous "ON” bi-clocks and two continuous “OFF” bi-clocks; and the remainder, one "ON” clock, is also arranged at the last clock of the first sub-cycle, as shown in phantom line.
- continuous "OFF" clocks are consequently divided and approximately uniformly distributed in a PWM cycle, and therefore the LED will be lit more frequently without flickering.
- the duty cycle is preserved as 9/16, so that brightness of the LED is the same for viewers.
Abstract
Description
- The present invention relates to a LED driving device with pulse width modulation (PWM).
- In general, brightness of an LED can be varied with the duty cycle of a control signal delivered from a driving IC (integrated circuit) device. When the LED is desired to perform lower brightness with a less duty cycle, an external control system will output a signal with longer continuous "OFF" to the driving IC device, so that the LED is not lit or lasts unilluminated for a longer time. In such situation, the LED display will flicker and show poor quality as it's apparently visible for viewers. FIG 1 compares the images without and with flickering.
- To prevent the LED display from flickering, the present invention provides a solution by dividing a continuous "ON" signal into many discrete "ON" signals and distributing them uniformly.
- The LED driving device with PWM primarily comprises a PWM unit and LED driving circuits. The LED driving device receives a preset value about brightness of the LED and delivers the preset value to the PWM unit. The PWM unit generates an ON/OFF signal with a duty cycle in a PWM cycle corresponding to the preset value and then modulates the ON/OFF signal. The modulated signal is output to the LED through the LED driving circuit to perform desired brightness. The PWM unit modulates the ON/OFF signal from one signal of higher gray-scale resolution to two or more signals of relatively lower gray-scale resolution, so that the LED will be lit more frequently with a higher refresh rate and brightness of the LED before and after modulation is exactly the same or similar to a viewer. Preferably, the duty cycle of the ON/OFF signal is preserved before and after modulation.
- The PWM cycle of the ON/OFF signal has a continuous "ON" duration composed of a major "ON" cycle and a minor "ON" cycle. The PWM unit modulates the ON/OFF signal by dividing the major "ON" cycle into two or more parts each defined as a major "ON" sub-cycle, and distributing the major "ON" sub-cycles in the PWM cycle according to an algorithm.
- The minor "ON" cycle may be ignored or further divided by the PWM unit into two or more parts each defined as a minor "ON" sub-cycle all of which are then distributed with the major "ON" sub-cycles. Preferably, the major "ON" cycle is evenly divided and uniformly distributed. The modulated signal output from the PWM unit is normally clock-based.
- In the specification, terms are defined as follows:
- 1. Pulse width modulation (PWM) cycle, being the time for completely performing a control signal about LED brightness.
- 2. Duty cycle, being a percentage of time for "ON" with respective to a period of the PWM cycle.
- 3. Refresh rate, being a frequency for lighting the LED.
- 4. Gray-scale resolution, being the scales of brightness which the LED possibly performs.
-
- FIG 1 compares the images without and with flickering.
- FIG 2 schematically illustrates clock diagrams of the control signal divided in accordance with different algorithms.
- To describe this invention more in detail, embodiments of algorithms for the PWM unit to modulate a signal are exemplified on the basis of the description in
- Note that the algorithms are not restricted and depend on developed computing techniques or technologies.
- Also note that "the duty cycle is preserved" in the invention doesn't indicate "the duty cycle is kept absolutely the same", but indicate no obvious difference for viewers. For example, the minor "ON" cycle could be ignored when being much less than the major "ON" cycle.
- In the following algorithms, variables n, m, k, M, A, B, i are defined as follows:
- n is a positive integer,
- m is 0 or a positive integer less than n,
- k is 0 or a positive integer less than m,
- M is a positive integer less than 2n
- A is 0 or a positive integer less than M,
- B is 0 or a positive integer less than 2k×2n-m-k; and
- i is 0 or a positive integer equal to or less than 2k.
-
- a. (2n-m-k+1) sub-cycles composed of 2n-m-k sub-cycles each having (2m-1)×2k clocks, and one sub-cycle having 2k×2n-m-k clocks, as represented by formula (I); or
- b. 2n-m-k sub-cycles each having 2m×2k clocks, as represented by formula (I-1). For the both algorithms, 2k is the frequency division factor applied to less division.
-
- a. (2n-m-k+1) sub-cycles composed of 2n-m-k sub-cycles each having A×2k clocks and one sub-cycles having B clocks, as represented by formula (II); or
- b. 2n-m-k sub-cycles each having (A×2k+i) clocks, wherein a sum of i from each sub-cycle is equal to B.
- With respect to the formulae (I) and (II), each of the sub-cycles having (2m-1)×2k clocks may comprise A×2k clocks for "ON", and one sub-cycle having 2k×2n-m-k clocks may comprise B clocks for "ON".
- With respective to formulae (I-1) and (II-1), each of the sub-cycles having 2m×2k clocks may comprise (A×2k+i) clocks for "ON".
- As a result, the LED display can exhibit an image with desired brightness and without flickering as the duty cycle is preserved and the refresh rate is increased. Also note that specific limitation to n or M is not necessary and depends on developments of photo-electric technologies.
- In an actual design, a 16-bit counter in the PWM unit is provided for a PWM cycle and thus may perform a resolution of 65,536 (=216) gray-scales. When the PWM cycle is divided into, for example, 64 (=26) sub-cycles, the resolution will be reduced to 1,024 (=210) gray-scales with a refresh rate 64.
- To illustrate the algorithms, schematically clock diagrams are shown in FIG 2. Diagram (a) indicates 16 reference clocks. Diagram (b) indicates an undivided PWM cycle composed of nine continuous "ON" clocks and seven continuous "OFF" clocks. That is, the duty cycle is 9/16. Examples (A) and (B) explain processes for
refresh rates - First, the formula (I) with k=0 is employed.
Then the clocks of diagram (a) are divided into four (22=4) equal sub-cycles each having four (22=4) clocks, as shown in diagram (c). The formula (II) is further employed to divide the nine "ON" clocks.
Then each sub-cycle comprises two continuous "ON" clocks and two continuous "OFF" clocks; and the remainder, one "ON" clock, may be arranged at the last clock of the first sub-cycle, as shown with phantom line. - The diagram (d) shows a result of the diagram (a) processed with a
frequency division factor 2, and each clock of the diagram (d) is defined as a bi-clock. The formula (I) is employed with k=1.
After dividing into two sub-cycles, each sub-cycle in the diagram (e) comprises four (22=4) bi-clocks and eight clocks. Formula (II) is then employed to divide the nine "ON" clocks.
Then each sub-cycle is composed of two continuous "ON" bi-clocks and two continuous "OFF" bi-clocks; and the remainder, one "ON" clock, is also arranged at the last clock of the first sub-cycle, as shown in phantom line. - As illustrated in the above examples, continuous "OFF" clocks are consequently divided and approximately uniformly distributed in a PWM cycle, and therefore the LED will be lit more frequently without flickering. Particularly, the duty cycle is preserved as 9/16, so that brightness of the LED is the same for viewers.
Claims (9)
- An LED driving device with PWM (pulse width modulation), comprising a PWM unit and an LED driving circuit, the LED driving device receiving a preset value about brightness of the LED and delivering the preset value to the PWM unit, the PWM unit generating an ON/OFF signal with a duty cycle in a PWM cycle corresponding to the preset value and then modulating the ON/OFF signal, the modulated signal being output to the LED through the LED driving circuit to perform desired brightness; wherein:the PWM unit modulates the ON/OFF signal from one signal of higher gray-scale resolution to two or more signals of relatively lower gray-scale resolution, so that the LED will be lit more frequently with a higher refresh rate and brightness of the LED before and after modulation is exactly the same or similar to a viewer.
- The LED driving device with PWM as claimed in claim 1, wherein the PWM cycle of the ON/OFF signal has a continuous "ON" duration composed of a major "ON" cycle and a minor "ON" cycle, and the PWM unit modulates the ON/OFF signal by dividing the major "ON" cycle into two or more parts each defined as a major "ON" sub-cycle, and distributing the major "ON" sub-cycles in the PWM cycle according to an algorithm.
- The LED driving device with PWM as claimed in claim 2, wherein the PWM unit further divides the minor "ON" cycle into two or more parts each defined as a minor "ON" sub-cycle all of which are then distributed with the major "ON" sub-cycles.
- The LED driving device with PWM as claimed in claim 2, wherein the major "ON" cycle is evenly divided and uniformly distributed.
- The LED driving device with PWM as claimed in claim 1, wherein the modulated signal output from the PWM unit is clock-based.
- The LED driving device with pulse width modulation as claimed in claim 2, wherein the PWM unit divides one PWM cycle having 2n clocks according to the formula (I):
wherein n is a positive integer, m is 0 or a positive integer less than n, k is
0 or a positive integer less than m;
accordingly, the PWM cycle may be divided either 2n-m-k+1 sub-cycles composed of 2n-m-k sub-cycles each having (2m-1)×2k clocks and one sub-cycle having 2k×2n-m-k clocks; or 2n-m-k sub-cycles each having 2m×2k clocks; wherein 2k is a frequency division factor. - The LED driving device with PWM as claimed in claim 2, wherein the PWM unit divides the continuous "ON" duration having M clocks in one PWM cycle according to formula (II):
wherein n, m and k are defined as the above, M is a positive integer less than 2n, A is 0 or a positive less than M, B is 0 or a positive integer less than 2k×2n-m-k;
accordingly, the major "ON" cycle has A×2k×2n-m-k clocks, and the minor "ON" cycle has B clocks; and M clocks are divided into either (2n-m-k+1) sub-cycles composed of 2n-m-k sub-cycles each having A×2k clocks and one sub-cycle having B clocks; or 2n-m-k sub-cycles each having (A×2k+i) clocks; wherein i is 0 or a positive integer equal to or less than 2k, and a sum of i from each sub-cycle is equal to Bo - The LED driving device with PWM as claimed in claim 2, wherein the PWM unit divides one PWM cycle having 2n clocks with M "ON" clocks as follows:a. dividing the PWM cycle into (2n-m-k+1) sub-cycles composed of 2n-m-k sub-cycles each having (2m-1)×2k clocks with A×2k "ON" clocks, and one sub-cycle having 2k×2n-m-k clocks with B "ON" clocks; orb. dividing the PWM cycle into 2n-m-k sub-cycles each having 2m×2k clocks with (A×2k+i) "ON" clocks;wherein n, m, k, M, A, B and i are defined as the above.
- The LED driving device with PWM as claimed in claim 1, wherein the duty cycle of the ON/OFF signal is preserved before and after modulation.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PL06005074T PL1814365T3 (en) | 2006-01-24 | 2006-03-13 | LED driving device with pulse width modulation |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CN200610001583A CN101009957B (en) | 2006-01-24 | 2006-01-24 | LED driving integrated circuit device with the adjustable pulse bandwidth |
Publications (2)
Publication Number | Publication Date |
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EP1814365A1 true EP1814365A1 (en) | 2007-08-01 |
EP1814365B1 EP1814365B1 (en) | 2012-05-23 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP06005074A Active EP1814365B1 (en) | 2006-01-24 | 2006-03-13 | LED driving device with pulse width modulation |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP1814365B1 (en) |
CN (1) | CN101009957B (en) |
ES (1) | ES2388069T3 (en) |
PL (1) | PL1814365T3 (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP2306441A1 (en) | 2009-09-30 | 2011-04-06 | Macroblock, Inc. | Scan-type display device control circuit |
US9468051B1 (en) | 2015-08-27 | 2016-10-11 | National Yunlin University Of Science And Technology | Light emitting diode linear light modulator with temperature compensation |
CN113793564A (en) * | 2021-09-16 | 2021-12-14 | 中科芯集成电路有限公司 | OSPWM algorithm for multi-interval optimization |
EP4211674A4 (en) * | 2020-09-09 | 2024-03-27 | Texas Instruments Inc | Light-emitting diode (led) display driver with blank time distribution |
Families Citing this family (8)
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CN102044211B (en) * | 2009-10-12 | 2013-06-12 | 聚积科技股份有限公司 | Scanning type display device control circuit |
CN102215620B (en) * | 2010-04-08 | 2014-05-28 | 明阳半导体股份有限公司 | Device and method for driving light-emitting diode (LED) |
CN101937648B (en) * | 2010-09-03 | 2012-07-04 | 南京德普达电子技术有限公司 | Ordinary constant flow source driving chip-based method for controlling grey scale display of light-emitting diode (LED) |
CN102054434B (en) * | 2010-12-21 | 2013-04-17 | 苏州君嬴电子科技有限公司 | Light-emitting diode (LED) display system and method having pulse scattering mode |
CN103000123A (en) * | 2012-08-29 | 2013-03-27 | 北京集创北方科技有限公司 | Pulse width regulating device |
CN103874270B (en) * | 2012-12-17 | 2016-04-20 | 普诚科技股份有限公司 | LED driving method and device |
TWI564858B (en) * | 2015-06-24 | 2017-01-01 | Macroblock Inc | Light - emitting diode control method |
CN105717436A (en) * | 2016-01-27 | 2016-06-29 | 江西联星显示创新体有限公司 | Detection method and system using CABC signals to change LED voltage automatically |
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US20020012008A1 (en) * | 2000-04-21 | 2002-01-31 | Yuichi Takagi | Modulation circuit, image display using the same, and modulation method |
US20030076048A1 (en) | 2001-10-23 | 2003-04-24 | Rutherford James C. | Organic electroluminescent display device driving method and apparatus |
US20030085749A1 (en) * | 2000-02-03 | 2003-05-08 | Koninklijke Philips Electronics N.V. | Supply assembly for a led lighting module |
US20050184933A1 (en) * | 2004-01-26 | 2005-08-25 | Kiyohide Tomohara | Display controller, display system, and display control method |
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EP1166604B1 (en) * | 2000-02-03 | 2006-06-14 | Koninklijke Philips Electronics N.V. | Supply assembly for a led lighting module |
-
2006
- 2006-01-24 CN CN200610001583A patent/CN101009957B/en active Active
- 2006-03-13 ES ES06005074T patent/ES2388069T3/en active Active
- 2006-03-13 EP EP06005074A patent/EP1814365B1/en active Active
- 2006-03-13 PL PL06005074T patent/PL1814365T3/en unknown
Patent Citations (4)
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US20030085749A1 (en) * | 2000-02-03 | 2003-05-08 | Koninklijke Philips Electronics N.V. | Supply assembly for a led lighting module |
US20020012008A1 (en) * | 2000-04-21 | 2002-01-31 | Yuichi Takagi | Modulation circuit, image display using the same, and modulation method |
US20030076048A1 (en) | 2001-10-23 | 2003-04-24 | Rutherford James C. | Organic electroluminescent display device driving method and apparatus |
US20050184933A1 (en) * | 2004-01-26 | 2005-08-25 | Kiyohide Tomohara | Display controller, display system, and display control method |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP2306441A1 (en) | 2009-09-30 | 2011-04-06 | Macroblock, Inc. | Scan-type display device control circuit |
TWI407415B (en) * | 2009-09-30 | 2013-09-01 | Macroblock Inc | Scan-type display control circuit |
US8760458B2 (en) | 2009-09-30 | 2014-06-24 | Macroblock, Inc. | Scan-type display device control circuit |
US9468051B1 (en) | 2015-08-27 | 2016-10-11 | National Yunlin University Of Science And Technology | Light emitting diode linear light modulator with temperature compensation |
EP4211674A4 (en) * | 2020-09-09 | 2024-03-27 | Texas Instruments Inc | Light-emitting diode (led) display driver with blank time distribution |
CN113793564A (en) * | 2021-09-16 | 2021-12-14 | 中科芯集成电路有限公司 | OSPWM algorithm for multi-interval optimization |
CN113793564B (en) * | 2021-09-16 | 2023-04-25 | 中科芯集成电路有限公司 | Multi-region optimization OSPWM algorithm |
Also Published As
Publication number | Publication date |
---|---|
PL1814365T3 (en) | 2012-11-30 |
CN101009957B (en) | 2010-05-12 |
CN101009957A (en) | 2007-08-01 |
EP1814365B1 (en) | 2012-05-23 |
ES2388069T3 (en) | 2012-10-08 |
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