Patent Application
20140246992
The present invention relates to power supplies, and more particularly, to switch mode power supplies (SMPS) configured to provide both an output voltage suitable for a given load and an internal regulated power supply.
A typical switch mode power supply (also called an SMPS) is a power supply that includes a switching regulator to efficiently convert electrical power. In particular, and like other power supply types, an SMPS receives power from a source, such as mains power, and converts that power to have certain voltage and current characteristics. The output voltage resulting from that conversion is then applied to a load (e.g., lighting elements, equipment, etc). Some SMPS configurations also call for an internal supply voltage to power the electronics of the SMPS, such as the switching control circuitry. This switching control circuitry is typically implemented with an integrated circuit (IC), such as a PFC controller. The internal supply voltage, which is sometimes referred to as an auxiliary voltage or VCC, is derived from the mains power using passive or active circuitry, which is generally referred to as the SMPS's startup circuitry. The SMPS may also be configured to regulate this internal voltage produced by the startup circuitry. Thus, an SMPS may be configured to provide a first regulated voltage (the output voltage) to a given load and a second regulated voltage (VCC) to internal circuitry of the SMPS.
As noted above, a switch mode power supply (SMPS) may be configured to provide both an output voltage to a given load as well as an internal voltage supply for internal electronics, such as but not limited to internal switching control circuitry. The output voltage for the load is typically generated by a converter, such as an AC-DC flyback converter, and the internal voltage supply is typically generated by a so-called startup circuit. With passive start-up circuits, however, the converter output voltage that drives the load can become unstable at a high AC mains voltage during light load conditions. Under such conditions, the additional gain provided by the startup circuit appears as an over voltage, which triggers dynamic over voltage protection (OVP) circuitry that is also present in the SMPS. When this occurs, the SMPS stops switching and then restarts when the internal gate drive is enabled. This stop-start behavior repeats until the light load condition clears.
Embodiments are disclosed that provide a stable output voltage in switching mode power supplies. In some embodiments, an SMPS is provided that includes a converter section for powering a load, a passive startup circuit for initially providing an internal voltage supply for powering the switching electronics of the SMPS when the mains is turned on, and a feedback circuit providing the internal voltage supply once the converter starts switching. The SMPS further includes a decoupling circuit that decouples the gain of the passive startup circuit from the feedback circuit, so as to prevent false dynamic OVP triggers. In some embodiments, the SMPS circuit is implemented with a flyback converter topology that is powered by a rectified AC line voltage. Of course, other SMPS topologies may be, and in some embodiments are, used as well, such as buck, boost, and buck-boost, as will be appreciated in light of this disclosure. The decoupling circuit is implemented, for example, with the addition of two or three passive components, such as but not limited to a diode and a capacitor, or a diode, a capacitor, and a resistor. Preventing false triggering of the dynamic OVP in turn provides a more stable output voltage. Numerous other embodiments and variations will be apparent in light of this disclosure.
In an embodiment, there is provided a power supply circuit. The power supply circuit includes: a controller; a switching converter comprising a transformer and a switch configured to be controlled by the controller, the switching converter configured to receive voltage from a voltage source and to provide an output voltage suitable to drive a load; a startup circuit having a gain and configured to receive voltage from the voltage source and to provide a startup voltage to the controller; a feedback circuit configured to provide a feedback voltage to the controller, the feedback voltage based on the output voltage of the converter; and a decoupling circuit operatively coupled to the feedback circuit and configured to isolate the feedback voltage from the gain of the startup circuit.
In a related embodiment, the transformer may include a three-winding transformer having a primary side winding, a secondary side winding, and a primary side bias winding, and the primary side bias winding may be part of the feedback circuit. In another related embodiment, the transformer may include a three-winding transformer having a primary side winding, a secondary side winding, and a primary side bias winding, and the primary side bias winding may be operably coupled to the feedback circuit.
In still another related embodiment, the controller may include overvoltage protection (OVP) circuitry that triggers in response to the feedback voltage being higher than a defined upper limit. In yet another related embodiment, the switching converter may be a flyback converter. In still yet another related embodiment, the startup circuit may be passive and may include a resistor connected in series with a capacitor. In a further related embodiment, the passive startup circuit and the switching converter may be configured to receive a rectified AC line voltage.
In another embodiment, there is provided a lighting system. The lighting system includes: a solid state lighting element; a switching converter comprising a transformer and a switch configured to be controlled by a control signal, the converter configured to receive voltage from a voltage source and to provide an output voltage suitable to drive the solid state lighting element; a controller configured to provide the control signal and comprising overvoltage protection (OVP) circuitry that triggers in response to a feedback voltage being higher than a defined upper limit, wherein the feedback voltage is based on the output voltage of the switching converter; a startup circuit having a gain and configured to receive voltage from the voltage source and to provide a startup voltage to the controller; a feedback circuit configured to provide the feedback voltage to the controller; and a decoupling circuit operatively coupled to the feedback circuit and configured to isolate the feedback voltage from the gain of the startup circuit.
In a related embodiment, the transformer may be a three-winding transformer including a primary side winding, a secondary side winding, and a primary side bias winding, and the primary side bias winding may be part of the feedback circuit. In another related embodiment, the transformer may be a three-winding transformer including a primary side winding, a secondary side winding, and a primary side bias winding, and the primary side bias winding may be operably coupled to the feedback circuit.
In still another related embodiment, the switching converter may be a flyback converter. In yet another related embodiment, the startup circuit may be passive and may include a resistor connected in series with a capacitor. In still yet another related embodiment, the lighting system may further include a rectifier configured to provide rectified AC voltage to the startup circuit and to the switching converter.
In another embodiment, there is provided a method. The method includes: providing, via a switching converter including a transformer and a switch configured to be controlled by a control signal, an output voltage suitable to drive a load; providing, via controller circuitry, the control signal; providing, via a startup circuit having a gain, a startup voltage to the controller circuitry; providing, via a feedback circuit, a feedback voltage to the controller circuitry, the feedback voltage based on the output voltage of the converter; and isolating, via a decoupling circuit, the feedback voltage from the gain of the startup circuit so as to prevent overvoltage protection (OVP) circuitry from falsely triggering.
In a related embodiment, the method may further include: rectifying an input AC voltage; and providing the rectified input AC voltage to the startup circuit and to the switching converter. In another related embodiment, the method may further include: processing an input voltage; and providing the processed input voltage to the startup circuit and to the switching converter.
In still another related embodiment, providing, via a switching converter including a transformer and a switch configured to be controlled by a control signal, an output voltage includes providing, via a switching converter including a transformer and a switch configured to be controlled by a control signal, an output voltage suitable to drive a lighting element, and wherein the method reduces flickering of the lighting element due to false triggering of the OVP circuitry. In yet another related embodiment, the method may further include triggering the OVP circuitry of the controller circuitry in response to a valid OVP condition.
The foregoing and other objects, features and advantages disclosed herein will be apparent from the following description of particular embodiments disclosed herein, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles disclosed herein.
As discussed above, the output voltage of a switching converter-based power supply circuit may become unstable when there is a high AC mains input voltage, particularly during light load conditions. Such power supply circuits may be, for example, a flyback converter-based power supply for use in solid state lighting applications, although various SMPS topologies and applications will be apparent in light of this disclosure. To further explain the stability problem, it may first be helpful to understand an example scenario where the instability may manifest. In more detail, a typical SMPS needs an internal supply voltage at startup equal to the turn-on threshold voltage of the controller IC used to control the converter's transistor (switching element). In some cases, this startup voltage may be supplied by a passive startup circuit. After startup, the SMPS may use a primary side auxiliary or bias winding connected to the flyback converter to provide VCC to the controller. The primary side bias winding may also provide output voltage regulation. In universal mains applications, a combination of high line voltage, light load conditions, and the additional gain provided by the passive startup circuit may decrease output voltage regulation, in some cases. The additional gain from the startup circuit may cause false triggering of dynamic OVP within the controller IC and limit the effectiveness of the SMPS when operated in wide load range applications. This is because false triggering of OVP causes the controller IC to temporarily stop switching the flyback converter transistor, which in turn causes the flyback output voltage and the internal supply voltage for the controller IC to be unstable. This instability may manifest in a number of ways, depending on the application. For example, in a lighting application, the instability may cause flickering of the lighting element, while in a communication application, the instability may cause messaging errors. An active startup circuit may be used, which may not cause the instability, but involves active componentry and the cost associated therewith. In addition, depending on the design of the active startup circuit, there may still be an additional gain that causes false OVP triggering thereby giving rise to the stability problem. In a lighting application, a light load condition may occur, for instance, when solid state lighting elements are used rather than incandescent or fluorescent lighting elements.
The rectified AC voltage is also output to the passive startup circuit 102, which includes a first resistor 107, a second resistor 108, and a polarized capacitor 109. The first resistor 107, the second resistor 108, and the polarized capacitor 109 are in series with each other. The first resistor 107 and the second resistor 108 are in series between the rectified voltage source 101 and the feedback circuit 117. The polarized capacitor 109 is also connected to a ground. The feedback circuit 117 is connected between the second resistor 108 and the polarized capacitor 109. The feedback circuit 117 includes the primary side bias winding 110c, which provides the internal voltage supply (VCC) to a controller or control IC (not shown in
The passive startup circuit 102 initially provides the internal supply voltage VCC for the controller when the AC mains are turned on, and in turn the gate drive of the controller operates the switching transistor 111. Once the flyback converter 103 starts switching, the primary side bias winding 110c provides VCC to the controller. As previously explained, the voltage on the primary side bias winding 110c reflects the secondary side voltage of the transformer 110 and also provides output voltage regulation. At high voltage values of the AC source 104, the output voltage represented by the feedback voltage between the fourth resistor 118 and the fifth resistor 119 may become further increased due to the gain of the passive startup circuit 102. This increase in the feedback voltage may trigger the dynamic OVP circuitry within the controller, thereby causing the controller to temporarily stop the switching transistor 111. This stop-and-start switching effect is an instability that may manifest in the load 114 (e.g., flickering light, etc). In controllers without dynamic OVP protection, the additional gain provided by the passive startup circuit 102 will result in increased signal level or gain higher than the internal controller reference, resulting in instability and loss of regulation of the output current/voltage. For example, at high input AC voltage, the additional gain may cause the output voltage/current to decrease from the nominal voltage/current due to added input signal from the startup circuit 102 to the feedback pin of the control IC. This in turn limits the design of very wide input voltage range converters (e.g., such as in the example case of 108 to 305VAC), especially when there is no DC-DC converter as a second stage supplying the load.
Thus, embodiments provide a stable output voltage by isolating the output voltage feedback loop (i.e., the feedback circuit 117) from the gain provided by the passive startup circuit 102. Decoupling the output voltage feedback from the passive startup circuit 102 inhibits false triggering of dynamic OVP, thus increasing the stability of the output voltage throughout a wide load range suitable for universal mains operation. In addition, decoupling of output voltage feedback from the passive startup circuit 102 prevents output current instability/loss of regulation, thus improving stable and regulated operation throughout wide input voltage range suitable for the desired load 114. Note that this result, in some embodiments, is achieved without an active startup circuit, which in turn decreases active component count, circuit complexity, power consumption, and cost.
Though lighting circuits having various converter types may benefit from isolating the output voltage feedback or control loop pin of a control IC from the startup circuit, for ease of description, embodiments are described with flyback converters including a primary side bias winding that provides a reflection of the secondary side of the flyback converter transformer. As will be appreciated, embodiments may also be, and sometimes are, implemented with a DC voltage source. In such embodiments, a wide operating range of DC source may cause problems with output voltage stability similar to a rectified AC source, and the techniques described herein may be implemented to stabilize the output voltage.
In
The controller (not shown in
As will be appreciated, the designations as to what is included in the feedback circuit 317 and the decoupling circuit 320 are provided for purposes of discussion and are not intended to implicate limitations as to a particular structure or circuit. In some embodiments, each of the feedback circuit 317 and the decoupling circuit 320 may effectively include the primary side bias winding 310c as well as the third resistor 316, though this is not shown in
In embodiments wherein the load 314 includes one or more solid state lighting elements, which may operate at lower load conditions compared to incandescent, fluorescent, or other lighting systems, periodic high voltages from the rectified AC voltage source 301 combined with gain from the passive startup circuit 302 may trigger OVP at the controller if the output voltage feedback is not isolated from the passive startup circuit 302. Triggering OVP causes the gate drive of the controller to stop switching the switching transistor 311 of the flyback converter 303 and thus creates flickering in the lighting load 314. Thus, the circuit shown in
In
As will be appreciated, the various values and particulars of the components change from one embodiment to the next, and will depend on the application at hand. In some embodiments, the circuits shown in
A reasonable tolerance (e.g., +/−1% or +/−5%) should be presumed if no example range is given. Note that these example values and components are not intended to limit the claimed invention but are provided to show example configurations. As will be further appreciated, the size and/or value of a given component will depend on the power level and other pertinent factors that will reveal themselves for a given application. Numerous other configurations will be apparent in light of this disclosure.
The methods and systems described herein are not limited to a particular hardware or software configuration, and may find applicability in many computing or processing environments. The methods and systems may be implemented in hardware or software, or a combination of hardware and software. The methods and systems may be implemented in one or more computer programs, where a computer program may be understood to include one or more processor executable instructions. The computer program(s) may execute on one or more programmable processors, and may be stored on one or more storage medium readable by the processor (including volatile and non-volatile memory and/or storage elements), one or more input devices, and/or one or more output devices. The processor thus may access one or more input devices to obtain input data, and may access one or more output devices to communicate output data. The input and/or output devices may include one or more of the following: Random Access Memory (RAM), Redundant Array of Independent Disks (RAID), floppy drive, CD, DVD, magnetic disk, internal hard drive, external hard drive, memory stick, or other storage device capable of being accessed by a processor as provided herein, where such aforementioned examples are not exhaustive, and are for illustration and not limitation.
The computer program(s) may be implemented using one or more high level procedural or object-oriented programming languages to communicate with a computer system; however, the program(s) may be implemented in assembly or machine language, if desired. The language may be compiled or interpreted.
As provided herein, the processor(s) may thus be embedded in one or more devices that may be operated independently or together in a networked environment, where the network may include, for example, a Local Area Network (LAN), wide area network (WAN), and/or may include an intranet and/or the internet and/or another network. The network(s) may be wired or wireless or a combination thereof and may use one or more communications protocols to facilitate communications between the different processors. The processors may be configured for distributed processing and may utilize, in some embodiments, a client-server model as needed. Accordingly, the methods and systems may utilize multiple processors and/or processor devices, and the processor instructions may be divided amongst such single- or multiple-processor/devices.
The device(s) or computer systems that integrate with the processor(s) may include, for example, a personal computer(s), workstation(s) (e.g., Sun, HP), personal digital assistant(s) (PDA(s)), handheld device(s) such as cellular telephone(s) or smart cellphone(s), laptop(s), handheld computer(s), or another device(s) capable of being integrated with a processor(s) that may operate as provided herein. Accordingly, the devices provided herein are not exhaustive and are provided for illustration and not limitation.
References to “a microprocessor” and “a processor”, or “the microprocessor” and “the processor,” may be understood to include one or more microprocessors that may communicate in a stand-alone and/or a distributed environment(s), and may thus be configured to communicate via wired or wireless communications with other processors, where such one or more processor may be configured to operate on one or more processor-controlled devices that may be similar or different devices. Use of such “microprocessor” or “processor” terminology may thus also be understood to include a central processing unit, an arithmetic logic unit, an application-specific integrated circuit (IC), and/or a task engine, with such examples provided for illustration and not limitation.
Furthermore, references to memory, unless otherwise specified, may include one or more processor-readable and accessible memory elements and/or components that may be internal to the processor-controlled device, external to the processor-controlled device, and/or may be accessed via a wired or wireless network using a variety of communications protocols, and unless otherwise specified, may be arranged to include a combination of external and internal memory devices, where such memory may be contiguous and/or partitioned based on the application. Accordingly, references to a database may be understood to include one or more memory associations, where such references may include commercially available database products (e.g., SQL, Informix, Oracle) and also proprietary databases, and may also include other structures for associating memory such as links, queues, graphs, trees, with such structures provided for illustration and not limitation.
References to a network, unless provided otherwise, may include one or more intranets and/or the internet. References herein to microprocessor instructions or microprocessor-executable instructions, in accordance with the above, may be understood to include programmable hardware.
Unless otherwise stated, use of the word “substantially” may be construed to include a precise relationship, condition, arrangement, orientation, and/or other characteristic, and deviations thereof as understood by one of ordinary skill in the art, to the extent that such deviations do not materially affect the disclosed methods and systems.
Throughout the entirety of the present disclosure, use of the articles “a” and/or an and/or the to modify a noun may be understood to be used for convenience and to include one, or more than one, of the modified noun, unless otherwise specifically stated. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
Elements, components, modules, and/or parts thereof that are described and/or otherwise portrayed through the figures to communicate with, be associated with, and/or be based on, something else, may be understood to so communicate, be associated with, and or be based on in a direct and/or indirect manner, unless otherwise stipulated herein.
Although the methods and systems have been described relative to a specific embodiment thereof, they are not so limited. Obviously many modifications and variations may become apparent in light of the above teachings. Many additional changes in the details, materials, and arrangement of parts, herein described and illustrated, may be made by those skilled in the art.
The present application claims priority of U.S. Provisional Application No. 61/772,483, entitled “IMPROVED PRIMARY SIDE CONTROL IN FLYBACK CONVERTER FOR POWER SUPPLY” and filed Mar. 4, 2013, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61772483 | Mar 2013 | US |
