Voltage converter and control method thereof

1. Field of the Invention

The invention relates to a voltage converter, and more particularly to a voltage converter which provides various control schemes according to a load thereof.

2. Description of the Related Art

Nowadays, voltage converters are widely used in various electronic products, such as portable electronic products, computer products, and so on. Operating time of an electronic product is determined according to conversion efficiency of a voltage converter therein.

A pulse width modulation (PWM) controller is one type of control scheme for a continuous time voltage converter, which generates a PWM signal to control a transistor coupled to an output inductor of the voltage converter. By adjusting the duty cycle of the PWM signal, the PWM controller controls the transistor to turn on or off. Thus, the voltage converter may continually output voltage within a specific voltage range. For example, the PWM controller increases the duty cycle of the PWM signal when a load of the voltage converter is heavy. On the contrary, the PWM controller decreases the duty cycle of the PWM signal when the load of the voltage converter is light.

When the load of the voltage converter is light, the voltage converter may control the PWM signal at a minimal duty cycle. However, a continuous PWM signal requires power for the voltage converter, thereby decreasing the conversion efficiency of the voltage converter.

Therefore, a voltage converter which has improved conversion efficiency in a light load condition is desired.

A voltage converter and a control method thereof are provided. An exemplary embodiment of a voltage converter for converting an input voltage into an output voltage, wherein the output voltage is output to a load is provided. The voltage converter comprises an input terminal receiving the input voltage, an output terminal outputting the output voltage to the load, an inductor coupled between the output terminal and a node, a first transistor coupled between the input terminal and the node, a pulse width modulation (PWM) controller, an amplifier, a detector and a switching circuit. The PWM controller generates a first control signal according to the output voltage and a first reference voltage. The amplifier generates a second control signal according to the output voltage and a second reference voltage. The detector detects a loading of the load to generate a switching signal. The switching circuit selectively couples one of the PWM controller and the amplifier to the first transistor according to the switching signal. The switching circuit controls the first transistor according to the second control signal when the amplifier is coupled to the first transistor, such that the first transistor is operated in a saturation region.

Furthermore, an exemplary embodiment of a control method for a voltage converter comprising a transistor and an inductor is provided. The voltage converter converts an input voltage received by the transistor into an output voltage via the inductor and outputs the output voltage, wherein the output voltage is output to a load. It is determined whether the voltage converter is operating in a light load condition by detecting a loading of the load. The transistor is controlled to operate in a saturation region when the voltage converter is operating in the light load condition. The transistor is controlled to operate in a linear region or a cut-off region when the voltage converter is not operating in the light load condition.

A detailed description is given in the following embodiments with reference to the accompanying drawings.

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1A shows a voltage converter according to an embodiment of the invention;

FIG. 1B shows a voltage converter according to another embodiment of the invention; and

FIG. 1C shows a voltage converter according to another embodiment of the invention.

The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.

FIG. 1A shows a voltage converter 100 A according to an embodiment of the invention. The voltage converter 100 A converts an input voltage V in received from an input terminal N in into an output voltage V out , and provides the output voltage V out to a load 170 via an output terminal N out . As shown in FIG. 1A , the voltage converter 100 A comprises a transistor M 1 , a transistor M 2 , an inductor L, a pulse width modulation (PWM) controller 120 , an amplifier 130 , a reference voltage generator 140 , a detector 150 and a switching circuit 160 . The transistor M 1 is coupled between the input terminal N in and a node N 1 , and the transistor M 2 is coupled between the node N 1 and a ground GND. The inductor L is coupled between the node N 1 and the output terminal N out . In the voltage converter 100 A, a current. I out is generated and sensed from the inductor L by controlling the operation statuses of the transistors M 1 and M 2 , so as to provide the output voltage V out , to the load 170 through the output terminal N out . In addition, a voltage V FB is generated by dividing the output voltage V out through the resistors R 1 and R 2 . The voltage V FB is fed back to the voltage converter 100 A to control the operation statuses of the transistors M 1 and M 2 , such that the output voltage V out is maintained within a specific voltage range. For example, the output voltage V out is maintained between a first voltage value and a second voltage value, wherein the first voltage value is larger than the second voltage value and a voltage difference between the first and second voltage values is determined according to actual applications. In one embodiment, the first voltage value is substantially equal to the second voltage value.

In the voltage converter 100 A, the PWM controller 120 generates the PWM signals PWM 1 and PWM 2 according to the feedback voltage V FB and a reference voltage V ref provided by the reference voltage generator 140 . Furthermore, the amplifier 130 generates a signal V error according to the feedback voltage V FB and the reference voltage V ref . In the embodiment, the amplifier 130 is an error amplifier, and the signal V error is an analog error signal. In addition, in other embodiments, the reference voltage generator 140 may provide different reference voltages to the PWM controller 120 and the amplifier 130 according to various designs and applications. The detector 150 detects and determines a loading of the load 170 according to the feedback voltage V FB , the current I out or a voltage of the node V I . Next, the detector 150 provides a switching signal SW to the switching circuit 160 according to the detected loading of the load 170 . Next, the switching circuit 160 couples the amplifier 130 to a control terminal of the transistor M 1 or couples the PWM controller 120 to the control terminal of the transistor M 1 according the switching signal SW. Therefore, the transistor M 1 is controlled by the signal V error or the PWM signal PWM 1 , and the transistor M 2 is controlled by the PWM signal PWM 2 .

In FIG. 1A , when it is detected that the loading of the load 170 has increased, i.e. a heavy load condition, the detector 150 generates the switching signal SW, and transmits it to the switching circuit 160 , so as to control the switching circuit 160 to couple the PWM controller 120 to the transistor M 1 , and then the transistor M 1 is controlled by the PWM signal PWM 1 . Thus, the transistor M 1 is operated in a linear region or a cut-off region, i.e. the transistor M 1 is turned on or turned off. It is to be noted that the transistor M 1 and transistor M 2 are synchronously switched for the voltage converter 100 A in a heavy load condition. For example, the transistor M 2 is turned off when the transistor M 1 is turned on, and the transistor M 2 is turned on when the transistor M 1 is turned off. In addition, when it is detected that the loading of the load 170 has decreased, i.e. a light load condition, the detector 150 generates the switching signal SW, and transmits it to the switching circuit 160 , so as to control the switching circuit 160 to couple the amplifier 130 to the transistor M 1 , and then the transistor M 1 is controlled by the signal V error . Thus, the transistor M 1 is operated in a saturation region. It is to be noted that the transistor M 2 is turned off in a light load condition.

As described above, the detector 150 determines that the voltage converter 100 A is operating in a light load condition or a light load condition according to the output voltage V out , the current I out or the voltage of the node N 1 . For example, a voltage value of the output voltage V out may decrease immediately when the loading of the load 170 is increased. Therefore, when the output voltage V out is decreased to a voltage level that is smaller than a second voltage value, the detector 150 determines that the voltage converter 100 A is operating in a heavy load condition according to the feedback voltage V FB which is a divided voltage of the output voltage V out . Next, the detector 150 controls the switching circuit 160 to couple the PWM controller 120 to the transistor M 1 . In the meantime, the PWM controller 120 adjusts the duty cycles of the PWM signals PWM 1 and PWM 2 to control the operation statuses of the transistors M 1 and M 2 according to the feedback voltage V FB , such that the output voltage V out is maintained between the first voltage value and the second voltage value. Similarly, when the current I out is increased to a current level that exceeds a first current value, the detector 150 determines that the voltage converter 100 A is operating in a heavy load condition according to the current I out , and then the detector 150 controls the switching circuit 160 to couple the PWM controller 120 to the transistor M 1 . In addition, the detector 150 also controls the PWM controller 120 to adjust the duty cycles of the PWM signals PWM 1 and PWM 2 , such that the current I out is maintained between a first current value and the second current value. The first current value is larger than the second current value, and a current difference between the first and second current values is determined according to actual applications. In one embodiment, the first current value is substantially equal to the second current value.

Furthermore, the detector 150 determines that the voltage converter 100 A is operating in a light load condition according to the feedback voltage V FB when the output voltage V out is increased to a voltage level that exceeds the first voltage value. Next, the detector 150 controls the switching circuit 160 to couple the amplifier 130 to the transistor M 1 , so as to provide the signal V error to the transistor M 1 . Similarly, the detector 150 determines that the voltage converter 100 A is operating in a light load condition according to the current I out when the current I out is decreased to a current level that is smaller than the second current value.

FIG. 1B shows a voltage converter 100 B according to another embodiment of the invention. In FIG. 1B , the detector 150 comprises a transistor MS, a resistor RS and a comparator 152 with hysteresis. The detector 150 generates a sense signal V s according to the voltage of the node N 1 , wherein the sense signal V s corresponds to the voltage of the node N 1 . Next, the comparator 152 compares the sense signal V s with a reference voltage V ref2 to generate a switching signal SW. As described above, the detector 150 is used to determine whether the voltage converter 100 B is operating in a light load condition or a heavy load condition according to the voltage of the node N 1 . When the sense signal V s is increased to a voltage level that exceeds a first transition voltage value of the comparator 152 , the detector 150 determines that the voltage converter 100 B is operating in a light load condition. On the contrary, the detector 150 determines that the voltage converter 100 B is operating in a heavy load condition when the sense signal V s is decreased to a voltage level that is smaller than a second transition voltage value of the comparator 152 , wherein the first transition voltage value is larger than the second transition voltage value. In one embodiment, the first transition voltage value is substantially equal to the second transition voltage value.

FIG. 1C shows a voltage converter 100 C according to another embodiment of the invention. Compared with the voltage converter 100 A of FIG. 1A , the voltage converter 100 C is an asynchronous converter. In the voltage converter 100 C, a diode D is coupled between the node N 1 and the ground GND, wherein an anode of the diode D is coupled to the ground GND and a cathode of the diode D is coupled to the node N 1 .

The voltage converters described in the embodiments may selectively operate in a low drop out mode or a PWM mode according to loading variation of the load thereof. As described above, the voltage converter is operated in a low drop out mode when a light load condition is detected and the voltage converter is operated in a PWM mode when the light load condition is not detected, thus obtaining higher conversion efficiency for the voltage converter.

While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. Those who are skilled in this technology can still make various alterations and modifications without departing from the scope and spirit of this invention. Therefore, the scope of the present invention shall be defined and protected by the following claims and their equivalents.