Apparatus and method for loosely regulated power converters

A method for improving a power converter's efficiency comprises detecting an input voltage of a power converter, determining an operation mode of the power converter based upon the input voltage of the power converter and generating a plurality of gate drive signals based upon a damped gain control, wherein the damped gain control is configured such that an output voltage of the power converter is in a range from a tightly regulated output voltage to an unregulated output voltage.

TECHNICAL FIELD

The present invention relates to a power converter, and, in particular embodiments, to a control mechanism for bus converter applications.

BACKGROUND

A telecommunication network power system usually includes an AC-DC stage converting the power from the AC utility line to a 48V DC distribution bus and a DC-DC stage converting the 48V DC distribution bus to a plurality of voltage levels for all types of telecommunication loads. Both stages may comprise isolated DC-DC converters. Isolated DC-DC converters can be implemented by using different power topologies, such as flyback converters, forward converters, half bridge converters, full bridge converters, LLC resonant converters and the like.

As technologies further advance, bus converters have been widely employed in the telecommunication industry. The bus voltages may be divided into three categories, a 12V bus voltage converted from a 48V input dc power supply, a 48V bus voltage converted from a 380V input dc power supply and a 12V bus voltage converted from a 380V input dc power supply. A bus converter not only converts the input voltage from a higher level to a lower level, but also provides isolation through a magnetic device such as transformers and/or the like.

The intermediate bus voltage such as 12V may function as an input power bus for a plurality of downstream non-isolated power converters. The downstream non-isolated power converters may be implemented as step-down dc/dc converters such as buck converters, step-up dc/dc converters such as boost converters, linear regulators, any combinations thereof. The downstream non-isolated power converters operate under a tight control loop so that fully regulated output voltages are fed into their respective loads.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention which provide a loosely regulated power converter may achieve high efficiency as well as a better regulation in comparison with an unregulated power converter.

In accordance with an embodiment, a converter comprises an input coupled to a power source, a plurality of power switches coupled to the input, a magnetic device coupled to the power switches and a controller coupled to the power switches, wherein the controller is configured to generate a plurality of gate drive signals for the power switches, and wherein the gate drive signals are arranged such that an output voltage of the converter is in between a fully regulated output voltage and an unregulated output voltage.

In accordance with another embodiment, a method comprises detecting an input voltage of a power converter, wherein the power converter comprises an input coupled to a power source, a plurality of power switches coupled to the input and a controller coupled to the power switches.

The method further comprises generating a plurality of gate drive signals for the power switches, wherein the gate drive signals are arranged such that an output voltage of the converter is in between a fully regulated output voltage and an unregulated output voltage.

In accordance with yet another embodiment, a method comprises detecting an input voltage of a power converter, determining an operation mode of the power converter based upon the input voltage of the power converter and generating a plurality of gate drive signals based upon a damped gain control, wherein the damped gain control is configured such that an output voltage of the power converter is in a range from a tightly regulated output voltage to an unregulated output voltage.

An advantage of a preferred embodiment of the present invention is improving a power converter's efficiency through a damped gain control scheme.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention will be described with respect to preferred embodiments in a specific context, namely a damped gain control scheme for bus converters. The invention may also be applied, however, to a variety of power converters including isolated power converters such as full-bridge converters, half-bridge converters, forward converters, flyback converters and/or the like, non-isolated power converters such as buck converters, boost converters, buck-boost converters and/or the like, resonant converters such as LLC resonant converters and/or the like. Hereinafter, various embodiments will be explained in detail with reference to the accompanying drawings.

FIG. 1illustrates a block diagram of a power converter in accordance with various embodiments of the present disclosure. The power converter100includes a power stage102and a control stage104. The control stage104is coupled to the power stage102through a plurality of gate drive signals.

The power stage102may be a full-bridge converter, a half-bridge converter, a forward converter, a flyback converter, a buck converter, a boost converter, a buck-boost converter, a resonant converter, a linear regulator and/or the like.

The control stage104, as shown inFIG. 1, detects signals from both the input of the power converter100and the output of the power converter100. In addition, based upon the detected signals, the control stage104may generate a plurality of gate drive signals, which are fed into the power stage102as shown inFIG. 1. The gate drive signals are used to control the switching elements (not shown) of the power stage102. As a result, the output voltage of the power converter100may vary in response to different gate drive signals.

It should be noted whileFIG. 1shows the control stage104may detect both the input of the power converter100such as VIN and the output of the power converter100such as VO, the control stage104may generate the gate drive signals based upon either the input or the output of the power converter100. For example, the control stage104may only detect the signal at the input of the power stage102and generate the gate drive signals based upon a feedforward control mechanism. On the other hand, the control stage104may only detect the signal at the output of the power stage102and generate the gate drive signals based upon a feedback control mechanism.

In sum, the control stage104may generate the gate drive signals based upon a feedforward control scheme, a feedback control scheme, any combinations thereof and/or the like.

The gate drive signals may determine a variety of power converter parameters such as duty cycle, phase, switching frequency, any combinations thereof and the like. For example, in a non-isolated switching regulator such as a buck converter, the output voltage of the power converter100may vary in response to the change of the duty cycle, which is determined by the gate drive signals. Furthermore, in a phase-shift bridge converter, the phase change may lead to an output voltage variation. Moreover, in a resonant converter such as an LLC resonant converter, a variation of the switching frequency of the resonant converter may lead to a voltage variation at the output of the LLC resonant converter. The power converter control characteristics described above are well known in the art, and hence are not discussed in further detail to avoid repetition.

In accordance with some embodiments, a damped gain control mechanism is employed by the control stage104. In particular, the control stage104may either increase or decrease a control variable (e.g., duty cycle, phase and/or switching frequency) of the power stage102from its targeted value under a tight control loop. For example, under a tight control loop, in response to an input voltage, the power stage102may operate at a tightly controlled duty cycle so as to maintain a regulated output. Under the damped gain control scheme, the power stage102may operate in a duty cycle band. In some embodiments, the power stage102may be of a duty cycle fixed at a point of the duty cycle band. Alternatively, the power stage102may be of a duty cycle swinging back and forth between a lower limit and an upper limit of the duty cycle band.

In accordance with an embodiment, the duty cycle band described above is in a range from about 90% of the tightly controlled duty cycle to about 110% of the tightly controlled duty cycle.

FIG. 2illustrates the voltage gain of the power converter shown inFIG. 1in accordance with various embodiments of the present disclosure. The horizontal axis ofFIG. 2represents the duty cycle of a power converter such as the power converter100shown inFIG. 1. The vertical axis ofFIG. 2represents a ratio of the output voltage of the power converter100to the input voltage of the power converter100.

A curve202illustrates a ratio of the output voltage to the input voltage when the duty cycle of the power converter varies from about zero to about the max duty cycle of the power converter. A circle on the curve202indicates a corresponding duty cycle at the horizontal axis and a corresponding ratio at the vertical axis when the output voltage of the power converter is regulated by a tight control loop. Throughout the description, the circle is alternatively referred to as a tightly controlled ratio.

In some embodiments, the power converter100may be loosely regulated. The loosely regulated power converter is similar to a power converter controlled by a control loop with a damped gain. Throughout the description, a loosely regulated control scheme is alternatively referred to as a damped gain control scheme.

As shown inFIG. 2, under a damped gain control scheme, the ratio of the output voltage to the input voltage may fall into a range indicated by the dashed rectangle204. In other words, when the duty cycle of a tightly regulated power converter is equal to 0.6, the damped gain control may make the power converter operate in a duty cycle band as indicated by the dashed rectangle204. In some embodiments, the ratio of a duty cycle under the damped gain control scheme to a duty cycle under a tight control scheme may be in a range from about 90% to about 110%.

An advantageous feature of the embodiment described above is that the power converter100may achieve high efficiency in comparison with a tightly controlled power converter. On the other hand, the power converter may be of a better regulation in comparison with an open-loop power converter.

FIG. 3illustrates a first illustrative control scheme of the power converter shown inFIG. 1in accordance with various embodiments of the present disclosure. The horizontal axis ofFIG. 3represents the input voltage of a power converter such as the power converter100shown inFIG. 1. As shown inFIG. 3, the input voltage is in a range from Vin (min) to Vin (max).

In some embodiments, Vin (min) is approximately equal to 36V and Vin (max) is approximately equal to 75 V. In alternative embodiments, Vin (min) is approximately equal to 36V and Vin (max) is approximately equal to 60 V.

The vertical axis ofFIG. 3represents the output voltage of the power converter100. In some embodiments, the output voltage is a typical telecommunication bus voltage such as 12 V, 5 V, 3.3 V and the like. In alternative embodiments, the output voltage is an intermediate bus voltage such as 48V, 12V and the like.

A first slope302represents the Vo-Vin relationship for the power converter when a tight control loop is employed. In other words, the first slope302is a Vo-Vin relationship of a fully regulated power converter. In particular, the line regulation such as the variation of the output voltage versus the variation of the input voltage is substantially small. In some embodiments, the line regulation as indicated by the slope302is less than or equal to 10%. In alternative embodiments, the line regulation is less than or equal to 5%.

It should be noted while the power converter100is fully regulated, the output voltage may be a slope rather than a straight line because some factors may cause voltage variations at the output of the power converter100. Such factors include line regulation, load regulation, temperature, any combinations thereof and/or the like.

A second slope304represents the Vo-Vin relationship for the power converter when an open-loop scheme is employed. In other words, the second slope304is a Vo-Vin relationship of an unregulated power converter. The voltage gain or the ratio of the output voltage to the input voltage may vary widely in response to different operation conditions. For example, a buck converter is of a 50% duty cycle in accordance with an open-loop control scheme. The buck converter's output voltage is about 50% of the input voltage.

A third slope306represents the Vo-Vin relationship for the power converter100when a damped gain control scheme is employed. As shown inFIG. 3, under the damped gain control scheme, the output voltage of the power converter falls between the fully regulated output voltage and the unregulated output voltage through a fixed duty cycle (e.g., 50% duty cycle).

It should be noted that the relative location of the third slope306shown inFIG. 3is merely an example. A person skilled in the art will recognize that depending on different applications and design needs, the third slope306may be located at any point in between the first slope302and the second slope304.

The damped gain control scheme may be achieved through a variety of implementations. For example, if the power converter is a dc/dc step-down converter such as a buck converter, the output voltage is insensitive to the variations of operation conditions (e.g., line, load and temperature changes) when the power converter operates under a tight control loop. On the other hand, the output voltage is almost proportional to the input voltage when the power converter operates under an open loop. The damped gain control scheme may force the power converter to operate at a duty cycle between the duty cycle of the fully regulated power converter and the duty cycle of the unregulated power converter.

It should further be noted whileFIG. 3shows the third slope306is linear, a person skilled in the art will recognize that the damped gain control scheme may be represented by a curve, a look-up table, any combinations thereof and/or the like,

FIG. 4illustrates a second illustrative control scheme of the power converter shown inFIG. 1in accordance with various embodiments of the present disclosure. As shown inFIG. 4, in response to different input voltages, two different control schemes may be employed accordingly. In particular, when the input voltage is in a range from Vin (min) to Vin (normal), the power converter operates under a tight control loop as indicated by the slope402. On the other hand, when the input voltage is in a range from Vin (normal) to Vin (max), the power converter operates under a damped gain control scheme as indicated by the slope404. The damped gain control scheme has been described above with respect toFIG. 3, and hence is not discussed again herein.

It should be should be noted that the location of Vin (normal) on the horizontal axis shown inFIG. 4is merely an example. A person skilled in the art will recognize that depending on different applications and design needs, Vin (normal) may be located at any point in between Vin (min) and Vin (max). For example, the Vin (normal) may be a predetermined threshold. The control stage (shown inFIG. 1) may determine the threshold based upon different applications and design needs.

FIG. 5illustrates a third illustrative control scheme of the power converter shown inFIG. 1in accordance with various embodiments of the present disclosure. The control schemes shown inFIG. 5are similar to those shown inFIG. 4except that the damped gain control scheme and the fully regulated control scheme are swapped as shown inFIG. 5. As shown inFIG. 5, the slope502represents the voltage gain under the damped gain control scheme. The slope504represents the voltage gain under a tight control loop.

FIG. 6illustrates a fourth illustrative control scheme of the power converter shown inFIG. 1in accordance with various embodiments of the present disclosure. The control schemes shown inFIG. 6are similar to those shown inFIG. 4except that the input voltage range is divided into three segments. In the first segments from Vin (min) to Vin (normal1), a damped gain control scheme is employed as indicated by the slope602. In the second segments from Vin (normal1) to Vin (normal2), a tight control scheme is employed as indicated by the slope604. In the third segments from Vin (normal2) to Vin (max), a damped gain control scheme is employed as indicated by the slope606.

It should be should be noted that the locations of Vin (normal1) and Vin (normal2) on the horizontal axis shown inFIG. 6are merely an example. A person skilled in the art will recognize that depending on different applications and design needs, Vin (normal1) and Vin (normal2) may be located at any point in between Vin (min) and Vin (max). For example, the Vin (normal1) and Vin (normal2) may be two threshold voltages determined by the control stage (shown inFIG. 1).

It should further be noted thatFIG. 6illustrates the input voltage range is divided into three segments. The number of segments illustrated herein is limited solely for the purpose of clearly illustrating the inventive aspects of the various embodiments. The present invention is not limited to any specific number of segments. In other words, the input voltage range may be divided into any number of segments. Moreover, the damped gain control mechanism may be applied to at least one segment of the input voltage range.

FIG. 7illustrates a fifth illustrative control scheme of the power converter shown inFIG. 1in accordance with various embodiments of the present disclosure. The control schemes shown inFIG. 7are similar to those shown inFIG. 6. In the first segments from Vin (min) to Vin (normal1), a tight control scheme is employed as indicated by the slope702. In the second segments from Vin (normal1) to Vin (normal2), a damped gain control scheme is employed as indicated by the slope704. In the third segments from Vin (normal2) to Vin (max), a tight control scheme is employed as indicated by the slope706.

It should be noted that the illustrative embodiments described are based upon a control scheme in response to a variation of the input voltage of a power converter. The various embodiments of the present application are applicable to the control schemes in response to other operation condition variations such as load current, temperature, output voltage, input voltage, any combinations thereof and/or the like.