Synchronous switch mode power supply and method of operating the synchronous switch mode power supply

Abstract

A synchronous switch mode power supply for converting an input at an input node to an output at an output node, comprising an energy storage component arranged for storing energy, a main switch arranged for transferring energy from the input to the energy storage component, a synchronous switch arranged for providing a current path for current flowing through the energy storage component when the main switch is deactivated, a diode placed in parallel over said synchronous switch, an output capacitor arranged for storing electrical energy at the output node, and a controller arranged for controlling the main switch and the synchronous switch, wherein said controller is arranged to disable control of said synchronous switch for high load conditions such that for high load conditions said converter operates as a non-synchronous converter.

Description

[0001] SYNCHRONOUS SWITCH MODE POWER SUPPLY AND METHOD OF OPERATING THE SYNCHRONOUS SWITCH MODE POWER SUPPLY

[0002] TECHNICAL FIELD

[0003] The present disclosure generally relates to the field of switch mode power supply and, more specifically, to switch mode power supplies capable of efficiently handling different load conditions.

[0004] BACKGROUND

[0005] A synchronous switch mode power supply, SMPS, represents an evolution in power conversion technology, offering advantages in efficiency and performance over traditional non-synchronous designs. At its core, this type of power supply utilizes active switches, typically Metal Oxide Semiconductor, MOS, Field Effect Transistors, FETs, MOSFETs, both for the main switching element and for synchronous rectification, i.e. the synchronous switch. This dual employment of MOSFETs facilitates synchronous operation, where the rectification process is actively controlled rather than relying on passive diodes. Such a configuration presents several benefits, including enhanced efficiency, reduced losses, and improved transient response.

[0006] In the operation of a synchronous SMPS, the electrical components play interconnected roles. Firstly, the energy storage component, commonly an inductor or transformer, serves as a reservoir for storing and releasing energy. During the on-state of the main switch, this component stores energy as current flows through it, generating a magnetic field. Subsequently, during the off-state of the main switch, the stored energy is released, maintaining a continuous current flow and ensuring efficient energy transfer to the output.

[0007] The main switch, typically a MOSFET, acts as the primary driver of energy transfer in the Switch Mode Power Supply. By cyclically switching on and off at certain frequencies, the main switch regulates the flow of energy from the input source to the energy storage component. This precise control mechanism allows for the modulation of output voltage and current levels.

[0008] Complementing the main switch, the synchronous switch operates in in a complementary manner to facilitate synchronous rectification. When the main switch is in the off-state, the synchronous switch provides a low-resistance path for current flow, effectively replacing the traditional diode rectification mechanism. This synchronous rectification process substantially reduces conduction losses, resulting in higher overall efficiency and improved power conversion performance.

[0009] Additionally, the output capacitor serves a role in, for example, stabilizing the output voltage of the SMPS. By smoothing out high-frequency ripple and noise generated during the switching process, the output capacitor may ensure a clean and consistent DC voltage output. This capacitor also aids in transient response, supplying immediate current to the load during sudden changes in load demand, thus maintaining output voltage stability.

[0010] While synchronous Switch Mode Power Supplies, SMPS, offer efficiency advantages, their performance can vary under different load conditions. At light loads, the fixed losses associated with switching and control circuitry may disproportionately impact overall efficiency. Strategies such as pulse frequency modulation, PFM, or burst mode operation are commonly employed to mitigate these losses by adjusting the switching frequency based on load demand, thereby improving efficiency at light loads.

[0011] Conversely, under heavy load conditions, synchronous SMPSs may excel due to the low on-resistance of the MOSFETs used in both switching and rectification. This characteristic may minimize conduction losses and may improve efficiency, making synchronous SMPSs well-suited for applications requiring high current output.

[0012] Nevertheless, challenges exist, particularly in dynamically changing load scenarios. Rapid fluctuations in load demand can challenge the regulation and efficiency of synchronous SMPSs.

[0013] Summarizing, synchronous switch mode power supplies represent a significant improvement in power conversion technology, offering improved efficiency and performance over traditional designs. By leveraging active components for both switching and rectification, synchronous SMPSs deliver enhanced efficiency, reduced losses, and improved transient response, making them ideal for a wide range of applications demanding high- performance power conversion solutions. However, challenges exist for ensuring that the efficiency of synchronous switch mode power supplies is high for different load conditions.

[0014] SUMMARY

[0015] It would be advantageous to achieve a synchronous switch mode power supply that is efficient for different load conditions. It would further be advantageous to achieve a corresponding method for operating such a synchronous switch mode power supply. In a first aspect of the present disclosure, there is provided a synchronous switch mode power supply for converting an input at an input node to an output at an output node and arranged to provide a regulated power to a load couplable to the output node, the synchronous switch mode power supply, comprising: an energy storage component arranged for storing energy; a main switch arranged for transferring energy from the input voltage to the energy storage component; a synchronous switch arranged for providing a current path for current flowing through the energy storage component when the main switch is deactivated; a diode placed in parallel over said synchronous switch; an output capacitor arranged for storing electrical energy at the output node; a controller arranged for controlling the main switch and the synchronous switch, wherein said controller is arranged to disable control of said low-side switch, when the load has a power requirement exceeding a high-power requirement threshold, such that said converter operates as a non-synchronous converter.

[0016] The synchronous switch mode power supply is used for powering a load. The load is coupled to the output node of the synchronous switch mode power supply. The synchronous switch mode power supply may provide a regulated power to the load. The load may require a relatively high power or a relatively low power compared to the power the synchronous switch mode power supply can provide. The load may be e.g. dimmed so that the load may demand from the synchronous switch mode power supply a power ranging from full power down to a very low power.

[0017] The inventors have found that typically, to guarantee soft switching under all types of load conditions, synchronous switch mode power supplies can be applied. Such switch mode power supplies comprise a main switch and a synchronous switch, which allow the positive and the negative peak current to be high enough to fully charge and discharge the halfbridge point.

[0018] However, due to higher circulating currents, such switch mode power supply may show higher losses compared to a switch mode power supply running in Boundary Condition Mode, BCM at high load conditions. A high load condition may occur in a situation where a relative high load can be considered a load having a power requirement exceeding a high-power requirement threshold. Normally, a switch mode power supply running in Boundary Condition Mode comprises a single switch, i.e. the main switch, and a diode for the synchronous part. Maintaining Boundary Condition Mode may result in high switching frequencies for relatively low loads.

[0019] To limit the switching frequency, such switch mode power supplies may enter Discontinuous Mode for light loads which may result in higher switching losses and Electromagnetic Interference, EMI, levels.

[0020] The present disclosure is directed to the concept of a synchronous switch mode power supply which may use the synchronous switch at low load conditions and may disable this synchronous switch, such that the diode is used, for high load conditions. In this way, the switching frequency can be limited without entering Discontinuous Mode.

[0021] It is noted that the working principle of the switch mode power supply is explained with reference to a buck converter. However, it is explicitly noted that the present disclosure may be used for different types of switch mode power supplies such as a Cuk converter, a boost converter or a flyback converter.

[0022] Boundary Conduction Mode, BCM, is a mode of operation in buck converters where the inductor current never reaches zero during the switching cycle. In this mode, the main switch and the diode may conduct simultaneously for a brief period, allowing the inductor current to flow continuously. This continuous current flow reduces switching losses and enables the converter to operate efficiently at moderate to heavy loads.

[0023] However, BCM operation necessitates higher switching frequencies to maintain continuous conduction, especially at light loads, which can lead to increased power losses and electromagnetic interference, EMI.

[0024] Discontinuous Mode, DCM, on the other hand, occurs when the inductor current drops to zero during a portion of the switching cycle. In this mode, the switch conducts for a shorter duration, resulting in discontinuous conduction of the inductor current. DCM operation is typically employed at light loads to limit the switching frequency and minimize power losses. However, the intermittent current flow during DCM operation can lead to higher switching losses and increased EMI levels compared to BCM operation.

[0025] Boundary Conduction Mode, BCM, and Discontinuous Mode, DCM, thus represent different operating conditions in switch mode power supplies. While BCM ensures continuous conduction of the inductor current throughout the switching cycle, DCM allows the inductor current to drop to zero during certain periods.

[0026] The present disclosure is thus directed to include the synchronous switch under light load conditions. For high load conditions the switch mode power supply may operate in Boundary Condition Mode. Doing so, the efficiency for higher load conditions is improved, whereas for light load conditions - where efficiency is less of an issue - the frequency can be limited by generating a negative peak current.

[0027] In an example, the controller is arranged to disable control of said synchronous switch when a load condition of said switch mode power supply is above a predetermined load condition.

[0028] By disabling the control of the synchronous switch, the diode is used.

[0029] In another example, the switch mode power supply further comprises: a current measurement circuit arranged for detecting a current drawn by a load connected to said switch mode power supply.

[0030] The controller may use the detected current for determining whether the controller needs to disable control of the synchronous switch. For example, when the detected current is above a predetermined threshold, the controller may decide to disable the control of the synchronous switch. More particularly, the controller may control the synchronous switch in such a way that the synchronous switch is “open”, such that the diode will ensure the corresponding current path.

[0031] In a further example, the switch mode power supply further comprises: a voltage measurement circuit arranged for detecting a voltage at an intermediate node, said intermediate node being a point where said synchronous switch connects to said energy storage component.

[0032] In yet another example, the controller is further arranged to disable control of said synchronous switch based on said detected voltage at said intermediate node.

[0033] In an even further example, the controller is further arranged to disable control of said synchronous switch based on a minimum value of said detected voltage at said intermediate node.

[0034] In one of the examples, the energy storage component is an inductor.

[0035] In yet another example, the controller is arranged to control said main switch and said synchronous switch based on a switching frequency, wherein said controller is further arranged to disable control of said synchronous switch based on said switching frequency.

[0036] In a further example, the controller is arranged to control said main switch and said synchronous switch based on a signal having a duty-cycle, wherein said controller is further arranged to disable control of said synchronous switch based on said duty-cycle.

[0037] In an even further example, the diode is implemented as a body diode in said synchronous switch. In another example, a lighting device comprises a switch mode power supply in accordance with any of the preceding claims and the load, wherein the load is a lighting load.

[0038] Preferably, the synchronous switch mode power supply provides power to a lighting load, which may be dimmable and therefore require a dynamic power. All over the dimming range, the control of the synchronous switch mode power supply is optimized and efficiency and other performances are improved.

[0039] In a second aspect of the present disclosure, there is provided a method of operating a switch mode power supply in accordance with any of the previous examples, wherein said method comprises the step of: controlling, by said controller, said main switch and said synchronous switch, disabling control, by said controller, of said main switch for high load conditions such that for high load conditions said switch mode power supply operates as a non-synchronous switch mode power supply.

[0040] It is noted that the advantages as explained with respect to the first aspect of the present disclosure, being the synchronous switch mode power supply, are also applicable to the second aspect of the present disclosure, being the method of operating a switch mode power supply.

[0041] In an example, the step of disabling said control of said main switch comprises disabling said control of said synchronous switch when said load condition is above a predefined load condition.

[0042] In an even further example, the step of disabling control of said synchronous switch is based on any of: a current drawn by a load connected to said switch mode power supply; a voltage detected on an intermediate node; a minimum voltage detected on said intermediate node; a switching frequency used for controlling said main switch and said synchronous switch; a duty-cycle of a signal used for controlling said main switch and said synchronous switch.

[0043] In a third aspect of the present disclosure, there is provided a computer program product comprising a computer readable medium having instructions stored thereon which, when executed by a controller of a switch mode power supply, cause said switch mode power supply to implement a method in accordance with any of the examples as provided above.

[0044] In the appended figures, similar components and / or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

[0045] The above and other aspects of the disclosure will be apparent from and elucidated with reference to the examples described hereinafter.

[0046] BRIEF DESCRIPTION OF THE FIGURES

[0047] Fig. 1 discloses a non-synchronous buck converter in accordance with the prior art;

[0048] Fig. 2 discloses waveforms for a buck converter running in Boundary Condition and Discontinuous Mode;

[0049] Fig. 3 discloses a synchronous buck converter in accordance with the present disclosure;

[0050] Fig. 4 discloses waveforms for a synchronous buck converter;

[0051] Fig. 5 discloses waveforms illustrating the generation of a negative peak current for light load conditions.

[0052] DETAILED DESCRIPTION

[0053] It is noted that in the description of the figures, same reference numerals refer to the same of similar components performing a same of essentially similar function.

[0054] A more detailed description is made with reference to particular examples, some of which are illustrated in the appended drawings, such that the features of the present disclosure may be understood in more detail. It is noted that the drawings only illustrate typical examples and are therefore not to be considered to limit the scope of the subject matter of the claims. The drawings are incorporated for facilitating an understanding of the disclosure and are thus not necessarily drawn to scale. Advantages of the subject matter as claimed will become apparent to those skilled in the art upon reading the description in conjunction with the accompanying drawings. The ensuing description above provides preferred exemplary embodiment s) only, and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the disclosure, it being understood that various changes may be made in the function and arrangement of elements, including combinations of features from different embodiments, without departing from the scope of the disclosure.

[0055] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." As used herein, the terms "connected," "coupled," or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, electromagnetic, or a combination thereof. Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or" in reference to a list of two or more items, covers all the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

[0056] These and other changes can be made to the technology considering the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein.

[0057] As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

[0058] Fig. 1 shows an example of a switch mode power supply, in this case a non- synchronous buck converter. There are five electrical components comprised by the buck converter. First, a main switch, typically a MOSFET, used to connect the supply voltage to the electrical energy storage component (inductor). Second, the inductor used to store electrical energy. Third, an output capacitor used to store electrical charge for, for example, stabilize the output signal during the off period of the switch. Fourth, a diode is used to prevent current running through this part of the circuit to the load but allows current to circulate during an off-time of the main switch. Lastly, a load. The magnitude of the load is of importance, in accordance with the present disclosure, for determining the switching frequency as, typically, the switching frequency depends on the magnitude of the current drawn by the load.

[0059] Fig. 2 shows waveforms for a buck converter, specifically for the peak current through the inductor.

[0060] In a non-synchronous buck converter operating in Boundary Conduction Mode, BCM, the waveform of the current through the inductor is similar to that of a synchronous buck converter. However, in a non-synchronous buck converter, the “freewheeling” diode is used instead of the synchronous switch to provide a path for the inductor current during the off-state of the main switch.

[0061] During the on-state of the main switch, i.e. the MOSFET as shown, the inductor current ramps up linearly as energy is stored in the inductor's magnetic field. This ramp-up period corresponds to the time when the main switch is conducting, and the inductor current increases steadily.

[0062] When the main switch turns off, the inductor current continues to flow through the load and the freewheeling diode in series. This phase, known as the freewheeling or flyback period, ensures continuous current flow through the load during the off-state of the main switch. The diode conducts to provide a path for the inductor current, preventing abrupt changes in current and voltage. As a result, the inductor current decreases gradually during this phase, maintaining a relatively smooth waveform.

[0063] Once the inductor current decreases to zero, the diode stops conducting, and the cycle repeats as the main switch turns on again. Throughout this process, the inductor current waveform resembles a sawtooth pattern, with a gradual rise during the on-state of the main switch and a gradual fall during the off-state, ensuring continuous energy transfer from input to output.

[0064] Fig. 3. Shows an alternative configuration for the buck converter, namely by replacing the diode by a synchronous switch: A synchronous switch mode power supply.

[0065] In a synchronous buck converter, a synchronous switch is used in place of the traditional freewheeling diode present in a non-synchronous buck converter (fig. 1). This synchronous rectifier provides a low-resistance path for the inductor current during the off- state of the main switch, minimizing losses and improving efficiency. By actively controlling the rectification process, synchronous buck converters can achieve higher efficiency and better performance, especially at high frequencies and under varying load conditions.

[0066] In a non-synchronous buck converter (fig. 1), a freewheeling diode is used for rectification during the off-state of the main switch. While this diode provides a path for the inductor current, it introduces additional losses due to its forward voltage drop, leading to slightly lower efficiency compared to synchronous buck converters.

[0067] Fig. 4 Shows the waveforms for such a synchronous converter of Fig. 3. As is clear from the figure, the peak current may become negative.

[0068] Fig. 5 shows more waveforms for the converter topology from Fig. 3. This shows different switching frequencies and switching points, depending on different load conditions. When a medium to full load is applied, the switching frequency is inherently lower, which means that switch mode power supply may be used in Boundary Condition mode, because that adds the advantage of lower circulating current.

[0069] With lower loads, it may be beneficial to ensure that the current may become negative, as this adds the advantage of having a lower switching frequency while not needing large peak currents, resulting in at least substantially low circulating currents.

[0070] In the examples provided, the switch mode power supply is arranged to provide a regulated power to a load. The load may be a lighting load, preferably a solid-state lighting load. Such a lighting load may be an LED or a laser diode.

[0071] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. The provided figures and descriptions of the embodiments of the invention are illustrative and explanatory to the heart of the invention and should not be seen as limiting the invention thereto. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

CLAIMS:

1. A synchronous switch mode power supply for converting an input at an input node to an output at an output node and arranged to provide a regulated power to a load couplable to the output node, the synchronous switch mode power supply comprising: an energy storage component arranged for storing energy; a main switch arranged for transferring energy from the input to the energy storage component; a synchronous switch arranged for providing a current path for current flowing through the energy storage component when the main switch is deactivated; a diode placed in parallel over said synchronous switch; an output capacitor arranged for storing electrical energy at the output node; a controller arranged for controlling the main switch and the synchronous switch, wherein said controller is arranged to disable control of said synchronous switch, when the load has a power requirement exceeding a high-power requirement threshold, such that said converter operates as a non-synchronous converter.

2. A synchronous switch mode power supply in accordance with claim 1, wherein said controller is arranged to disable control of said synchronous switch when a load condition of said switched mode power supply is above a predetermined load condition.

3. A switch mode power supply in accordance with any of the previous claims, wherein said switched mode power supply further comprises: current measurement circuit arranged for detecting a current drawn by a load connected to said switched mode power supply.

4. A switch mode power supply in accordance with claim 3, wherein said controller is arranged to disable control of said synchronous switch when said detected current is above a predetermined threshold.

5. A switch mode power supply in accordance with any of the previous claims, wherein said switched mode power supply further comprises: a voltage measurement circuit arranged for detecting a voltage at an intermediate node, said intermediate node being a point where said synchronous switch connects to said energy storage component.

6. A switch mode power supply in accordance with claim 5, wherein said controller is further arranged to disable control of said synchronous switch based on said detected voltage at said intermediate node.

7. A switch mode power supply in accordance with claim 6, wherein said controller is further arranged to disable control of said synchronous switch based on a minimum value of said detected voltage at said intermediate node.

8. A switch mode power supply in accordance with any of the previous claims, wherein said energy storage component is an inductor.

9. A switch mode power supply in accordance with any of the previous claims, wherein said controller is arranged to control said main switch and said synchronous switch based on a switching frequency, wherein said controller is further arranged to disable control of said synchronous switch based on said switching frequency.

10. A switch mode power supply in accordance with any of the previous claims, wherein said controller is arranged to control said main switch and said synchronous switch based on a signal having a duty-cycle, wherein said controller is further arranged to disable control of said synchronous switch based on said duty-cycle.

11. A lighting device comprising a switch mode power supply in accordance with any of the preceding claims and the load, wherein the load is a lighting load.

12. A method of operating a switch mode power supply in accordance with any of the previous claims, wherein said method comprises the step of: controlling, by said controller, said main switch and said synchronous switch,disabling control, by said controller, of said main switch for high load conditions such that for high load conditions said switched mode power supply operates as a non-synchronous switched mode power supply.

13. A method in accordance with claim 12, wherein said step of disabling said control of said main switch comprises disabling said control of said synchronous switch when said load condition is above a predefined load condition.

14. A method in accordance with any of the claims 11 - 13, wherein said step of disabling control of said synchronous switch is based on any of: a current drawn by a load connected to said switched mode power supply; a voltage detected on an intermediate node; a minimum voltage detected on said intermediate node; a switching frequency used for controlling said main switch and said synchronous switch; a duty-cycle of a signal used for controlling said main switch and said synchronous switch.

15. A computer program product comprising a computer readable medium having instructions stored thereon which, when executed by a controller of a switched mode power supply, cause said switched mode power supply to implement a method in accordance with any of the claims 12 - 14.

Images