Patents by Inventor Kai-Ji Chen
Kai-Ji Chen has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).
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Patent number: 8049690Abstract: A circuit and a method for driving light emitting diodes (LEDs) are provided. First, an input voltage is converted into an output voltage and the output voltage is transmitted to the anode terminals of LED strings. The output voltage is reduced when the output voltage is greater than a first threshold voltage and the output voltage is reduced when the lowest level among the cathode terminal voltages of all the LED strings is greater than a second threshold voltage. Thus, the output voltage can be maintained at a lower level for driving all the LED strings to reduce unnecessary power wastage.Type: GrantFiled: April 18, 2008Date of Patent: November 1, 2011Assignee: Himax Analogic, Inc.Inventors: Chin-Lung Wu, Chun-Kai Wang, Kai-Ji Chen
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Patent number: 7830202Abstract: The present invention discloses a current mirror circuit generating an output current flowing through an output current path according to an input current flowing through an input current path. The current mirror circuit comprises a P type transistor in the output current path, an operational amplifier, and a basic circuit. The operational amplifier has a negative input coupled to a node receiving the input current, a positive input coupled to a drain of the P type transistor, and an output coupled to a gate of the P type transistor. The basic circuit comprises a first transistor in the input current path and a second transistor in the output current path. The first transistor has a gate and a drain coupled together. The second transistor has a gate coupled to the gate of the first transistor.Type: GrantFiled: April 8, 2008Date of Patent: November 9, 2010Assignee: Himax Analogic, Inc.Inventors: Kai-Ji Chen, Shin-Wen Gu
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Patent number: 7768212Abstract: An LED driver circuit and its control circuit for controlling its power switch are provided. The LED driver includes a switch, a PWM controller, a current source and a signal controller. The switch has a first end outputting a driving voltage to at least one LED. The PWM controller provides a PWM signal. The current source provides a driving current flowing through the LED when a dimming control signal is asserted. The signal controller turns off the switch when the dimming control signal is de-asserted and relays the PWM signal from the PWM controller to the switch so that the switch is controlled by the PWM signal when the dimming control signal is asserted.Type: GrantFiled: April 15, 2008Date of Patent: August 3, 2010Assignee: Himax Analogic, Inc.Inventors: Kai-Ji Chen, Ching-Yi Wu
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Patent number: 7741787Abstract: A light-emitting diode driving circuit includes a control circuit, a transistor switch and a compensating circuit. The control circuit receives an oscillating signal to generate a pulse drive signal. The transistor switch is activated by the pulse drive signal such that an inductor is charged by an input voltage, in which the inductor is arranged to deliver an inducting current to at least one light-emitting diode when the transistor switch is deactivated. The compensating circuit is coupled between the control circuit and a capacitor provided for reducing ripples of an output voltage corresponding to the inducting current. The compensating circuit performs a charging and discharging operation along with the capacitor when controlled by a dimming control signal provided to control brightness of the light-emitting diode.Type: GrantFiled: April 11, 2008Date of Patent: June 22, 2010Assignee: Himax Analogic, Inc.Inventors: Kai-Ji Chen, Chin-Lung Wu
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Publication number: 20090230881Abstract: An LED driver circuit and its control circuit for controlling its power switch are provided. The LED driver includes a switch, a PWM controller, a current source and a signal controller. The switch has a first end outputting a driving voltage to at least one LED. The PWM controller provides a PWM signal. The current source provides a driving current flowing through the LED when a dimming control signal is asserted. The signal controller turns off the switch when the dimming control signal is de-asserted and relays the PWM signal from the PWM controller to the switch so that the switch is controlled by the PWM signal when the dimming control signal is asserted.Type: ApplicationFiled: April 15, 2008Publication date: September 17, 2009Applicant: HIMAX ANALOGIC, INC.Inventors: Kai-Ji Chen, Ching-Yi Wu
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Publication number: 20090207109Abstract: A circuit and a method for driving light emitting diodes (LEDs) are provided. First, an input voltage is converted into an output voltage and the output voltage is transmitted to the anode terminals of LED strings. The output voltage is reduced when the output voltage is greater than a first threshold voltage and the output voltage is reduced when the lowest level among the cathode terminal voltages of all the LED strings is greater than a second threshold voltage. Thus, the output voltage can be maintained at a lower level for driving all the LED strings to reduce unnecessary power wastage.Type: ApplicationFiled: April 18, 2008Publication date: August 20, 2009Applicant: HIMAX ANALOGIC, INC.Inventors: Chin-Lung Wu, Chun-Kai Wang, Kai-Ji Chen
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Publication number: 20090200959Abstract: A light-emitting diode driving circuit includes a control circuit, a transistor switch and a compensating circuit. The control circuit receives an oscillating signal to generate a pulse drive signal. The transistor switch is activated by the pulse drive signal such that an inductor is charged by an input voltage, in which the inductor is arranged to deliver an inducting current to at least one light-emitting diode when the transistor switch is deactivated. The compensating circuit is coupled between the control circuit and a capacitor provided for reducing ripples of an output voltage corresponding to the inducting current. The compensating circuit performs a charging and discharging operation along with the capacitor when controlled by a dimming control signal provided to control brightness of the light-emitting diode.Type: ApplicationFiled: April 11, 2008Publication date: August 13, 2009Applicant: HIMAX ANALOGIC, INC.Inventors: Kai-Ji Chen, Chin-Lung Wu
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Publication number: 20090153126Abstract: The present invention discloses a current mirror circuit generating an output current flowing through an output current path according to an input current flowing through an input current path. The current mirror circuit comprises a P type transistor in the output current path, an operational amplifier, and a basic circuit. The operational amplifier has a negative input coupled to a node receiving the input current, a positive input coupled to a drain of the P type transistor, and an output coupled to a gate of the P type transistor. The basic circuit comprises a first transistor in the input current path and a second transistor in the output current path. The first transistor has a gate and a drain coupled together. The second transistor has a gate coupled to the gate of the first transistor.Type: ApplicationFiled: April 8, 2008Publication date: June 18, 2009Inventors: Kai-Ji Chen, Shin-Wen Gu
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Patent number: 7495503Abstract: A current biasing circuit is provided, which is designed to suppress reference current drift caused by temperature variation with a low overall temperature coefficient of a constant-voltage circuit and at least one resistor. The constant-voltage circuit comprises a diode and/or a diode-connected transistor. This current biasing circuit is based on a current mirror architecture, is easy to implement, and is a relatively temperature-independent current source.Type: GrantFiled: May 14, 2007Date of Patent: February 24, 2009Assignee: Himax Analogic, Inc.Inventors: Kai-Ji Chen, Ching-Wei Hsueh
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Publication number: 20080284502Abstract: A current biasing circuit is provided, which is designed to suppress reference current drift caused by temperature variation with a low overall temperature coefficient of a constant-voltage circuit and at least one resistor. The constant-voltage circuit comprises a diode and/or a diode-connected transistor. This current biasing circuit is based on a current mirror architecture, is easy to implement, and is a relatively temperature-independent current source.Type: ApplicationFiled: May 14, 2007Publication date: November 20, 2008Applicant: HIMAX ANALOGIC, INC.Inventors: Kai-Ji Chen, Ching-Wei Hsueh