Patent Application
20150070954
1. Field of the Invention
The present invention relates to a controller for power conversion, especially to a controller having an adjustable frequency-reduction function to provide appropriate switching frequencies for different power conversion applications.
2. Description of the Related Art
As energy efficiency is more and more demanded globally, regulations for power supplies are becoming more and more stringent. Taking the California Energy Commission as an example, it proposed an efficiency level 4 regulation on Jul. 1, 2006, an efficiency level 5 regulation on Nov. 1, 2008, and an efficiency level 6 regulation—a DOE (Department of Energy) regulation—on Jul. 1, 2013. The required efficiency of a power supply has been continually pushed upward step by step. For example, a 12 W power supply is requested to have an efficiency of not less than 72.4% for the efficiency level 4, not less than 74.74% for the efficiency level 5, and not less than 79.94% for the efficiency level 6.
The change from the efficiency level 5 to the efficiency level 6 involves an efficiency improvement of 5.2%. As the components of general power supplies have been designed to have nearly approached their best efficiencies, it is very difficult for a power supply to meet the requirement of the efficiency level 6.
The power consumption of a power supply depends mostly on the switching frequency the power supply is operating at—the higher the switching frequency is, the larger the power consumption will be. To further improve the efficiency of a power supply, one solution utilizing a frequency-reduction mechanism has been proposed. The principle of the frequency-reduction mechanism is that—a controller of the power supply will reduce the switching frequency when a feedback voltage from a load falls below a preset threshold voltage, wherein the feedback voltage reflects the loading condition of the power supply in a way as follows: the feedback voltage will become lower when the loading becomes lighter, and will become higher when the loading becomes heavier.
However, as the preset threshold voltage is a fixed voltage and is generated inside the controller, different power conversion applications using the same controller will have different energy efficiency, and the efficiency level 6 is therefore still not attained.
To solve the foregoing problem, a novel controller is needed.
One objective of the present invention is to disclose a controller having an adjustable frequency-reduction function for power conversion applications to reduce their power consumption.
Another objective of the present invention is to disclose a controller having an adjustable frequency-reduction function for power conversion applications to meet the requirement of the efficiency level 6.
Another objective of the present invention is to disclose a controller having an adjustable frequency-reduction function and being compatible with the existing structures of general power conversion systems.
Still another objective of the present invention is to disclose a controller having an adjustable frequency-reduction function to reduce the power consumption of general power conversion systems without interfering with the designs for safety regulation thereof.
To attain the foregoing objectives, a controller having an adjustable frequency-reduction function for a power conversion application is proposed, including:
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.
The present invention will be described in more detail hereinafter with reference to the accompanying drawings that show the preferred embodiments of the invention.
Please refer to
The controller 100 includes a threshold voltage sampling unit 101, a PWM (pulse width modulation) unit 102, and a driver unit 103.
The threshold voltage sampling unit 101 has a first node coupled to the resistor network 150 for generating a threshold voltage VX at the first node, which is then sampled by the threshold voltage sampling unit 101. The threshold voltage sampling unit 101 provides a constant current IS when the power transistor 110 is on to generate the threshold voltage VX, which is equal to −VIN*(Na/Np)*R2/(R1+R2)+IS*R2, wherein Na is a turn number of an auxiliary coil 121 of the power transmission unit 120, Np is a turn number of a primary coil 122 of the power transmission unit 120, R1 is the resistance of a resistor 151 of the resistor network 150, and R2 is the resistance of a resistor 152 of the resistor network 150. The threshold voltage sampling unit 101 generates a first threshold voltage Va according to a first function of the threshold voltage VX, a second threshold voltage Vb according to a second function of the threshold voltage VX, and a third threshold voltage Vc according to a third function of the threshold voltage VX, wherein Va>Vb>Vc. The first function, the second function, and the third function are preferably but not limited to first order polynomial functions of VX. For example, Va can be equal to K1*VX+Vdc1, Vb can be equal to K2*VX+Vdc2, and Vc can be equal to K3*VX+Vdc3, wherein K1, K2, K3, Vdc1, Vdc2, and Vdc3 are constants.
The PWM unit 102 has a second node for receiving a feedback voltage VFB from the load 160 via the feedback circuit 140, a third node for providing a PWM signal VPWM of a switching frequency, and a fourth node for receiving a current sensing signal VCS from the current sensing resistor 130. The PWM unit 102 adjusts the duty of the PWM signal VPWM in response to VFB and VCS, so as to generate the output voltage VO. To reduce power consumption of the power converter, the PWM unit 102 adjusts the switching frequency of the PWM signal VPWM in response to VFB in a way as illustrated in
The driver unit 103 is used for generating a driving signal VG to drive the power transistor 110 according to the PWM signal VPWM.
The power transistor 110, illustrated as an NMOS transistor in the figure though, can also be implemented with a bipolar transistor. The power transistor 110 is used to control a power transmission of the power transmission unit 120 from VIN to the load 160.
The power transmission unit 120 includes the auxiliary coil 121, the primary coil 122, a secondary coil 123, a diode 124, and a capacitor 125 to transmit power from VIN to the load 160 under the control of the power transistor 110. As the principle of the power transmission unit 120 is well known, it is not addressed here.
The current sensing resistor 130 is used to convert a primary current IP to the current sensing signal VCS.
The feedback circuit 140 is used to generate the feedback voltage VFB according to a difference between the output voltage VO and a reference voltage (not shown in the figure).
When the controller 100 is used in different power conversion applications, the resistance of the resistor 151 and the resistance of the resistor 152 can be adjusted to generate appropriate values of the threshold voltage VX for the different power conversion applications, so as to meet the requirement of the efficiency level 6.
Based on the principle elaborated above, the present invention proposes another embodiment. Please refer to
The controller 300 includes a threshold voltage sampling unit 301, a PWM unit 302, and a driver unit 303.
The threshold voltage sampling unit 301 has a first node coupled to a resistor network consisting of the first resistor 330 and the second resistor 331 for generating a threshold voltage VX at the first node, which is then sampled by the threshold voltage sampling unit 301. The threshold voltage sampling unit 301 provides a constant current IS when the power transistor 310 is off to generate the threshold voltage VX, which is equal to IS*(R1+R2), wherein R1 is the resistance of the first resistor 330, and R2 is the resistance of the second resistor 331. The threshold voltage sampling unit 301 generates a first threshold voltage Va according to a first function of the threshold voltage VX, a second threshold voltage Vb according to a second function of the threshold voltage VX, and a third threshold voltage Vc according to a third function of the threshold voltage VX, wherein Va>Vb>Vc. The first function, the second function, and the third function are preferably but not limited to first order polynomial functions of VX. For example, Va can be equal to K1*VX+Vdc1, Vb can be equal to K2*VX+Vdc2, and Vc can be equal to K3*VX+Vdc3, wherein K1, K2, K3, Vdc1, Vdc2, and Vdc3 are constants.
As the principles of the remaining parts have been described above with reference to
With the designs elaborated above, the present invention possesses the following advantages:
While the invention has been described by way of example and in terms of preferred embodiments, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
In summation of the above description, the present invention herein enhances the performance over the conventional structure and further complies with the patent application requirements and is submitted to the Patent and Trademark Office for review and granting of the commensurate patent rights.
