Power converters are essential for many modern electronic devices. Among other capabilities, power converters can adjust voltage level downward (buck converter) or adjust voltage level upward (boost converter). Power converters may also convert alternating current (AC) power to direct current (DC) power, or vice versa. Power converters are typically implemented using one or more switching devices, such as transistors, which are turned on and off to deliver power to the output of the converter.
Klein, U.S. Pat. No. 7,457,140, entitled, “POWER CONVERTER WITH HYSTERETIC CONTROL”, refers to a method for hysteretic control of a DC-to DC power converter, and is incorporated by reference herein in its entirety.
This document discusses, among other things, an apparatus and method for receiving an input signal at a hysteric controller, such as a hysteretic controller for a power converter, and providing an output signal, including providing a reference signal to a hysteretic comparator of the hysteric controller and providing a feedback signal to the comparator, wherein the feedback signal includes an AC component of a switch signal and a DC component of the output signal.
This overview is intended to provide an overview of subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application.
In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.
In certain power converters applications, the load current may vary significantly (e.g., over several orders of magnitude), in which case it can be desirable to have rapid response in the regulation or control of the converters. In an example, certain power converters can use pulse-width modulation (PWM) to control the on-time of a switch connected to a supply (e.g., an unregulated DC input). In a hysteretic power converter, a ramp waveform, for example, derived from current flow of the converter, is maintained between two threshold values to control a switching circuit, or power train module, of the converter. In an example, a hysteretic regulator can turn on a switching device of a power converter when Vout is below a first threshold voltage (e.g., 5V), and can turn off the switching device of the converter when Vout is above a second threshold voltage.
In certain examples, a hysteretic control circuit provides control information to control a first switch and a second switch. In an example, the first switch can connect a first voltage, such as input voltage, to an inductor. In this example, a second switch can connect a second voltage, such as a ground to the inductor. In this example, the first and second switches can be controlled by the hysteretic control circuit, and can be turned on in a mutually-exclusive manner. In an example, the first and second switches can toggle between conducting and non-conducting states, such as to keep an instantaneous output voltage within a specified range. The specified range can be proportional to a hysteresis “window” around a desired output voltage, the window including an upper (e.g., peak) threshold and a lower (e.g., valley) threshold.
In certain examples, the output voltage can increase when the first switch is conducting, such as when the inductor current is positive and flowing towards a load resistance, or decrease, when the second switch is conducting. The increase or decrease in output voltage can be periodic, such as when the regulator circuit has stabilized and is driving the load. In certain examples, the variation in output voltage is caused by the regulator, and the regulator circuit is thus called a “ripple regulator” or “bang-bang” regulator.
In an example, many previous PWM and hysteretic controllers cannot go into or out of 100% duty cycle conveniently, nor do they deal with an external Vout feedback resistive divider easily (e.g., requiring an error-amplifier to act as an integrator). Further, many previous hysteretic controllers require a reference voltage of the main comparator to be the same as the output voltage of the power converter, adding more design constraints to the main comparator and reference generator.
The present inventors have recognized, among other things, that a coupling circuit can be added to a hysteretic controller, for example, to allow the main comparator input voltage to be different than the final output voltage of the controller. Further, in certain examples, a coupling circuit can allow a hysteretic controller to use a voltage divider feedback structure without requiring an integrator circuit. In an example, the coupling resistance can be significantly higher than the resistance of the feedback network to decouple the values of a feedback network (e.g., an external feedback resistor divider) from the loop parameters of the hysteretic controller. In an example, a coupling circuit can enable hysteretic controllers to go into and out of 100% duty cycle conveniently, and can enable use of the external Vout feedback resistive divider without requiring an error amplifier, and without requiring a minimum load to prevent the error amplifier from drifting away. In addition, a hysteretic controller incorporating a coupling circuit as described below can maintain robust load-transient response.
In certain examples, the coupling circuit 214 of the hysteretic controller 201 can provide design flexibility not available using the architecture illustrated in
Another benefit of the coupling circuit is the flexibility in selecting the voltage divider components. For example, a coupling circuit having a coupling capacitance of 11 pF and a coupling resistance of 500 kOhms was monitored with two significantly different voltage divider networks. In a first example, the voltage divider resistances were 2.5 kOhms and 8.65 kOhms. In a second example, the voltage divider resistances were 70 kOhms and 242 kOhms, significantly high than the resistances of the first example. The resulting plots of the load voltage, inductor current and load current were substantially the same even when the load current underwent significant step increases and significant step decreases. Thus, the coupling circuit allows significant flexibility in selecting the size of the voltage divider components.
Certain examples can be beneficial in applications having a load voltage very close to the supply voltage, having a high load current and/or where a voltage divider feedback is desired. USB buck regulators and DC-DC buck regulator requiring good load transient response are example applications for which a hysteretic controller having a coupling circuit as described above can be especially useful.
In certain examples, an integrated circuit can include a hysteretic controller. In some examples, an integrated circuit hysteretic controller can be coupled to an external inductor. In some examples, an integrated circuit hysteretic controller can couple to an external feedback network to allow flexibility in using the controller for different applications. In some examples, an integrated circuit hysteretic controller can couple to an external power train module.
The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples.” All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.
In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.
The above description is intended to be illustrative, and not restrictive. For example, although the examples above have been described relating to MOSFET devices, one or more examples can be applicable to bipolar devices. In other examples, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.
This application claims the benefit of priority under 35 U.S.C. §119(e) to Tao, U.S. Provisional Patent Application Ser. No. 61/330,252, entitled “AC COUPLED HYSTERETIC PWM CONTROLLER,” filed on Apr. 30, 2010 (Attorney Docket No. 2921.051PRV), which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | |
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61330252 | Apr 2010 | US |