Low power electrical conversion

Abstract

An apparatus and a method for use in electrical conversion are described. The apparatus comprises signal processing and switch circuitry that can process an AC mains signal for determining when best to convert the AC mains signal to a DC signal in the AC mains signal cycle.

Description

[0001] Low Power Electrical Conversion

[0002] The present invention relates to a method and apparatus for use in the conversion of an AC grid (or mains) signal to provide a DC output signal. In particular, the present invention is directed toward methods and apparatus for converting an AC mains signal to provide a low level DC power signal (e.g., a USB-C power supply, or the like) suitable for meeting ‘standby’ power needs of electronic devices.

[0003] Typically, in AC-to-DC power conversion systems a bridge rectifier, or the like, is provided to rectify an AC signal to produce a varying DC output. One disadvantage associated with the use of such bridge rectifiers however is that the DC output varies significantly, varying between substantially the peak input AC magnitude and zero. One technique that is commonly used to reduce the variation in the DC output signal is to provide a smoothing capacitor connected across the output of the bridge rectifier. That smoothing capacitor in use may be cyclically charged and discharged as appropriate to smooth the output DC signal such that it has minimal variation between the peak input AC magnitude and zero.

[0004] Alternatively, by way of example only, to reduce the variation in the DC output signal or to reduce the output voltage level, a step-down DC-to-DC converter, or a Buck-Boost DC-to-DC converter may be used.

[0005] However, whilst such DC-to-DC power converters (e.g., step down and / or Buck-Boost) help to ensure the provision of a stable and regulated output voltage across the load, inefficiencies in AC-to-DC power conversion systems that utilise such DC-to-DC power converters still persist. For example, when a continuous low power needs to be provided to an electronic device (e.g., when it is operating in a standby mode, or the like), conversion of a whole AC cycle of an AC mains signal may result in inefficiencies in power conversion, particularly at high voltage points.

[0006] There is therefore a need to develop improved AC-to-DC power conversion systems that minimise energy losses during AC-to-DC conversion of an AC mains signal and / or subsequent DC-to-DC conversion of the resultant DC signal, especially in the context of low- power provision to electronic devices (e.g., when providing power to an electronic device operating in a standby mode).

[0007] Summary of Invention

[0008] Embodiments of the invention provide apparatus for converting an alternating current, AC, mains signal to a direct current, DC, signal for powering an electronic device, the apparatus comprising: means for receiving the AC mains signal; conversion circuitry for converting the AC mains signal or a signal derived from the AC mains signal (such as a rectified signal) into the DC signal for powering the electronic device; switching circuitry for receiving the AC mains signal or the signal derived from the AC mains signal and for selectively applying the AC mains signal or the signal derived from the AC mains signal to the conversion circuitry; and processing circuitry for processing the AC mains signal or the signal derived from the AC mains signal to determine periods of time in the vicinity of zero crossing points of the AC mains signal and configured to control the switching circuitry so that during said periods of time in the vicinity of said zero crossing points, the AC mains signal or the signal derived from the AC mains signal is applied to the conversion circuitry and so that during periods of time in the vicinity of peaks of the AC mains signal, the switching circuitry does not apply said AC mains signal or the signal derived from the AC mains signal to said conversion circuitry.

[0009] The conversion circuitry may comprise a capacitor that maintains the DC output from the conversion circuitry during periods of time when the AC mains signal or the signal derived from the mains signal is not applied to the conversion circuitry.

[0010] In some embodiments, the processing circuitry may be configured to detect zero crossing points of the AC mains signal and to determine said periods of time in the vicinity of zero crossing points of the AC mains signal using said crossing points and a timer.

[0011] In some embodiments, the processing circuitry is configured to determine periods of time in the vicinity of said peaks of the AC mains signal or the signal derived from the AC mains signal and is configured to determine said periods of time in the vicinity of said zero crossing points using the determined periods of time in the vicinity of said peaks of the AC mains signal or the signal derived from the AC mains signal.

[0012] The processing circuitry may be configured to determine said periods of time in the vicinity of zero crossing points of the AC mains signal by comparing the AC mains signal or the signal derived from the AC mains signal with a threshold. The comparing may determine if the AC mains signal is above or below the threshold. In some embodiments, the processing circuitry is configured to compare the AC mains signal or the signal derived from the AC mains signal with a threshold by applying the AC mains signal or the signal derived from the AC mains signal to a filter circuit defining the threshold.

[0013] The processing circuitry may be formed from analogue circuit components, digital circuit components or a mix of analogue and digital circuit components. Where digital signal processing circuitry is provided, it may be configured to use a frequency transform processing technique to generate a digital representation of the AC mains signal and may determine said periods of time in the vicinity of the zero crossing points of the AC mains signal using said digital representation of the AC mains signal.

[0014] Typically, the apparatus comprises rectifier circuitry for rectifying the AC mains signal to generate a rectified signal corresponding to said signal derived from the AC mains signal. In this case, the processing circuitry may be configured to receive the AC mains signal and the switching circuitry may be configured to receive the rectified signal from the rectifier circuitry and to pass the rectified signal to the conversion circuitry during said periods of time in the vicinity of the zero crossing points of the AC mains signal. In alternative embodiments, the processing circuitry may receive the rectified signal from the rectifier circuitry and use it to determine the periods of time in the vicinity of the zero crossing points of the AC mains signal.

[0015] In some embodiments, the processing circuitry is configured to receive the AC mains signal and the switching circuitry is configured to receive the AC mains signal and to pass the AC mains signal to the conversion circuitry during said periods of time in the vicinity of the zero crossing points of the AC mains signal.

[0016] The conversion circuitry will typically comprise DC to DC conversion circuitry. It may in addition or alternatively comprise AC to DC conversion circuitry.

[0017] Embodiments of the invention also provide a method of converting an alternating current, AC, mains signal to a direct current, DC, signal for powering an electronic device, the method comprising: receiving the AC mains signal; using conversion circuitry to convert the AC mains signal or a signal derived from the AC mains signal into the DC signal for powering the electronic device; using switching circuitry to receive the AC mains signal or the signal derived from the AC mains signal and to selectively apply the AC mains signal or the signal derived from the AC mains signal to the conversion circuitry; and processing the AC mains signal or the signal derived from the AC mains signal to determine periods of time in the vicinity of zero crossing points of the AC mains signal, to control the switching circuitry so that during said periods of time in the vicinity of said zero crossing points, the AC mains signal or the signal derived from the AC mains signal is applied to the conversion circuitry and so that during periods of time in the vicinity of peaks of the AC mains signal, the switching circuitry does not apply said AC mains signal or the signal derived from the AC mains signal to said conversion circuitry. Brief Description of Figures

[0018] Examples of apparatus and methods will now be described, by way of example, with reference to the accompanying drawings in which:

[0019] Figure 1a illustrates a first circuit arrangement for converting an AC grid signal into a DC signal for provision to an electrical device I load with signal processing and switch control circuitry positioned before any converters;

[0020] Figure 1b illustrates an alternative first circuit arrangement for converting an AC grid signal into a DC signal for provision to an electrical device I load with signal processing and switch control circuitry positioned after at least one converter;

[0021] Figure 2a illustrates an example of a typical AC grid signal;

[0022] Figure 2b illustrates an example square wave signal illustrating time periods when control circuitry forming part of Figure 1 controls a switch to cause a rectified version of the AC mains signal to be applied to DC to DC conversion circuitry forming part of Figure 1 ;

[0023] Figure 3 illustrates a second circuit arrangement for converting an AC grid signal into a DC signal for provision to an electrical device I load;

[0024] Figure 4a illustrates the typical AC grid signal shown in Figure 2a;

[0025] Figure 4b illustrates an example square wave signal representing the regions in which the typical AC grid signal of Fig. 4a is at or near its maximum voltage value that can be generated by signal processing circuitry;

[0026] Figure 4c illustrates an example square wave signal representing the regions in which the typical AC grid signal of Fig. 4a is at or near its minimum voltage value that can be generated by signal processing circuitry;

[0027] Figure 5a illustrates an illustrates an example step down DC-to-DC converter that may be implemented in the first and second circuit arrangements of Figs. 1 and 3 respectively; and

[0028] Figure 5b illustrates an illustrates an example Buck-Boost DC-to-DC converter that may be implemented in the first and second circuit arrangements of Figs. 1 and 3, respectively.

[0029] Overview

[0030] Fig. 1 illustrates a first example circuit arrangement that may be used to facilitate the passing of the AC grid signal 102 to an electrical converter for AC-to-DC conversion and an electrical converter for DC-to-DC conversion for provision of DC power to an electronic device (e.g., a load across Vout of the circuit).

[0031] As shown in Fig. 1 there is provided an AC source 101 (which is typically a mains supply but it could be from on-site AC generating circuitry) that provides the AC grid (or mains) signal 102 that is provided to signal processing and switching circuitry 104 to process the AC grid signal 102. For example, the signal processing part of the signal processing and switch control circuitry 104 may be configured to: determine regions / portions of the AC grid signal where it is at (or near) to its maximum voltage value; determine the regions / portions of the AC grid signal where it is at (or near) to its minimum voltage value; and / or determine locations (vicinities) where the voltage of the AC grid signal is non-zero and low (e.g., close to the zero crossing points, in the region of the zero crossing points etc.).

[0032] It will be appreciated that in the case of the determinations outlined above, the signal processing part of the signal processing and switch control circuitry 104, rather than determining regions / portions of the AC grid signal, may instead determine timings associated with when the AC grid signal is: at (or near) to its maximum voltage value; at (or near) to its minimum voltage value; and / or at a region where the voltage of an AC grid signal is at or near zero.

[0033] Having determined regions / locations where the voltage of the AC grid (mains) signal is nonzero and low (e.g., close to the zero crossing points, in the region of the zero crossing points etc.), the switch control part of the signal processing and switching circuitry 104 sends an appropriate signal (e.g., a control signal, or the like), to the switch 110 to either trigger the switch closed or trigger the switch open.

[0034] As shown in Fig. 1 the AC mains signal 102 is also provided to an appropriate AC-to-DC converter 106 (e.g., a bridge rectifier circuit, or the like) for rectifying (converting) the AC grid signal 102 into a high voltage DC (HVDC) signal.

[0035] When the control signal triggers the closing of the switch 110, the HVDC output signal from the AC-to-DC converter 106 (e.g., a bridge rectifier, or the like) is provided to a DC-to-DC converter 108 (e.g., a step down converter, Buck-Boost converter, or the like) for conversion of the HVDC signal to a low voltage DC signal usable in an electrical device which may be placed across Vout 112. Examples of the circuitry associated with step down converter and a Buck-Boost converter will be described in more detail later with reference to Fig 5.

[0036] Once the HVDC signal has been converted to a low voltage DC signal it may then be provided to an electrical load (e.g., an electrical device) to provide power to that electrical load.

[0037] Alternatively, when the control signal triggers the opening of the switch 110 the HVDC output signal from the AC-to-DC converter 104 (e.g., a bridge rectifier, or the like) is not provided to the DC-to-DC converter 306 (e.g., a step down converter, Buck-Boost converter, or the like).

[0038] In this scenario, a low voltage DC signal may still be provided to the electrical load (e.g., the electrical device) across the circuit if there is a capacitor in the DC-to-DC converter 108 that has charge on it. In this case, the capacitor in the DC-to-DC converter 108 may discharge across the electrical load (e.g., the electrical device), thereby providing power to the electrical load.

[0039] It will be appreciated that while in Fig. 1 the signal processing and switch control circuitry 104 is configured to receive the AC grid signal 102, it could, instead be configured to receive the rectified signal output from the AC-to-DC converter 106 - as shown in Fig. 1b.

[0040] It will also be appreciated that while the description of Fig. 1 describes the signal processing and switch control circuitry 104 collectively, the first circuit arrangement may nevertheless comprise separate the signal processing circuitry and switch control circuitry.

[0041] Control of Switch 110

[0042] The control of the switch 110 by the signal processing and switch control circuitry 104 may be based on a determination by the signal processing circuitry of when the AC grid signal 102 is at a low voltage ( / .e., far removed from its peak voltage value).

[0043] For example, Fig. 2a depicts a typical AC grid (mains) signal 102 operating at 240 / 1 lOVolts and a frequency of 50 / 60Hz. In regions of the AC grid signal 102 where it is determined by the signal processing circuitry that the AC grid signal 102 is at a low voltage - as shown in Fig. 2b - the switch control circuitry sends an appropriate control signal to trigger the switch 108 to close, thereby enabling the rectified AC grid signal ( / .e., the HVDC signal) to be passed on to the DC-to-DC converter 108 (e.g., conversion circuitry) for conversion to a low DC signal for provision to the electrical load 112.

[0044] Alternatively, in regions of the AC grid signal 102 where it is determined by the signal processing circuitry that the AC grid signal 102 is at or close to its peak voltage, the switch control circuitry sends an appropriate control signal to trigger the switch 108 to open, thereby preventing the rectified AC grid signal (J.e., the HVDC signal) to be passed on to the DC-to- DC converter 108 e.g., conversion circuitry) for conversion to a low DC signal for provision to the electrical load 112.

[0045] Beneficially by controlling the switch 108 to only be closed when the voltage of the AC grid signal 102 is close to zero (e.g., close to its zero crossing points), only those portions of the AC grid signal 102 that have the smallest voltage are passed to the DC-to-DC converter for conversion from a HVDC signal to a low voltage DC signal. By only using those portions of the AC grid signal 102 that have the smallest voltage, the conversion losses that typically occur when converting high voltage mains electrical signals to DC voltages are avoided, and thus overall efficiency gains are achieved by the circuit.

[0046] Thus, the switch 110 is opened and closed two times in every cycle of the AC grid signal 102. It is of course not essential to perform this switching every cycle of the AC grid signal 102. The benefits of invention can still be achieved if this switching is carried out in only some of the cycles of the AC grid signal 102 - although in this case the efficiency savings would be reduced.

[0047] Signal Processing - First circuit arrangement

[0048] There now follows a description of the signal processing that may be performed by the signal processing circuitry to process the AC mains signal 102 to determine when the switching circuitry should trigger switch 108 to open or close as described above.

[0049] In one example, the signal processing circuitry 104 may determine regions / portions of the AC grid signal 102 where it is at (or near) to its maximum voltage value and its minimum voltage value by applying thresholds. For example, as shown in Fig. 2a, a (pre)configured / defined maximum voltage threshold - ThresholdMax- may be set such that a region / portion of the AC grid signal 102 is determined to be a region / portion of the AC grid signal 102 at (or near) to its maximum voltage value when the voltage of the AC grid signal 102 is above the (pre)configured / defined maximum voltage threshold. An example of a maximum voltage threshold may be 60 Volts. Other thresholds could of course be used.

[0050] Similarly, as shown in Fig. 2a, a (pre)configured / defined minimum voltage threshold - ThresholdMin - may also be set and the signal processing circuitry 104 may use that minimum voltage threshold to determine a region / portion of the AC grid signal 102 that is at (or near) to its minimum voltage value. For example, the signal processing circuitry 104 may determine that a region / portion of the AC grid signal 102 is at (or near) to its minimum voltage value when the voltage of the AC grid signal 102 is more negative than the (pre)configured / defined minimum voltage threshold. An example of the minimum voltage threshold may be -60 Volts. Other thresholds could of course be used.

[0051] In another example, the signal processing circuitry 104 may determine the regions / portions of the AC grid signal 102 where it is at (or near) the zero crossing points of the AC grid signal 102 and use them to control one or more timers to determine periods when the switch 110 should be open and when it should be closed. For example, having determined that the voltage of the AC grid signal 102 has reached zero ( / .e., having determined a zero crossing point of the AC grid signal 102), the signal processing and switch control circuitry 104 may start a timer and deem that the AC grid signal 102 is close to the zero crossing (and so the switch 110 should be closed) until the timer reaches a predetermined value. Another timer (or the same timer counting to different values) can then be used to determine the periods when the AC grid signal 102 is close to its positive or negative peaks - during which times, the switch 110 should be opened.

[0052] It will be appreciated that by determining the zero crossing points of the AC grid signal 102 in this way and using it and the timer as described above, only the low voltage part of the AC signal after the zero crossing points may be fed into the DC-DC converter 108.

[0053] In yet another example, the signal processing circuitry 104 may determine the regions / portions of the AC grid signal 102 where it is at (or near) to its maximum voltage value and its minimum voltage value using digital signal processing (DSP) techniques. For example, the signal processing circuitry 104 may use frequency transform techniques to generate a digital representation of the AC grid signal (one that is synchronised with the actual AC grid signal 102). The signal processing circuitry 104 can then use that digital representation of the AC grid signal 102 to determine the regions / portions of the AC grid signal 102 when it is at (or near) to its maximum / minimum voltage value and / or at or near its zero crossing points.

[0054] Alternative circuit arrangement

[0055] Fig. 3 illustrates a second example circuit arrangement that may be used to facilitate the passing of the AC grid signal 302 to an electrical converter for AC-to-DC conversion (e.g., conversion circuitry) and an electrical converter for DC-to-DC conversion (e.g., conversion circuitry) for provision of DC power to an electronic device.

[0056] As shown in Fig. 3 there is provided an AC source 301 that provides the AC grid (mains) signal 302 that is provided to signal processing circuitry 304 to process the AC grid signal 302. For example, the signal processing circuitry may be configured to: determine regions / portions of the AC grid signal where it is at (or near) to its maximum voltage value; determine the regions / portions of the AC grid signal where it is at (or near) to its minimum voltage value; and / or determine regions / portions of the AC grid signal where it is close to its zero crossing points.

[0057] It will be appreciated that in the case of determinations outlined above, the signal processing part of the signal processing and switch control circuitry 304, rather than determining regions / portions of the AC grid signal, may instead determining timings associated with when the AC grid signal is: at (or near) to its maximum voltage value; at (or near) to its minimum voltage value; and / or at a region where the voltage of an AC grid signal is non-zero and low.

[0058] Having determined regions / locations where the voltage of the AC grid (mains) signal is nonzero and low (e.g., close to the zero crossing points) and / or regions / portions of the AC grid signal 302 where it is near its maximum / minimum level, the switch control circuitry 304 sends an appropriate signal (e.g., a control signal, or the like), to the switch 310 to either trigger the switch closed or trigger the switch open.

[0059] As shown in Fig. 3 the AC mains signal 302 may be provided to an appropriate AC-to-DC converter 306 (e.g., a bridge rectifier, or the like) for rectifying (converting) the AC grid signal 102 into a high voltage DC (HVDC) signal depending on whether a control signal from the switching circuitry triggers the closing of the switch 310. It will be appreciated that the AC-to- DC converter 306 may also more simply be referred to as ‘conversion circuitry’.

[0060] For example, when the control signal triggers the closing of the switch 310, the AC mains signal 302 is provided to the AC-to-DC converter 304 (e.g., a bridge rectifier, or the like) for conversion to a HVDC signal, which is then in turn provided to a DC-to-DC converter 308 (e.g., a step down converter, Buck-Boost converter, or the some other appropriate form of conversion circuitry) for conversion of the HVDC signal to a low voltage DC signal usable in an electrical device which may be placed across Vout 312.

[0061] Examples of the circuitry associated with step down converter and a Buck-Boost converter will be described in more detail later with reference to Fig 5.

[0062] Once the HVDC signal has been converted to a low voltage DC signal it may then be provided to an electrical load (e.g., an electrical device) to provide power to that electrical load. Alternatively, when the control signal triggers the opening of the switch 310 the AC mains signal 302 is not provided to the AC-to-DC converter 304 for conversion to a HVDC signal. In this scenario, a low voltage DC signal may still be provided to the electrical load (e.g., the electrical device) across the circuit if there is a capacitor in the DC-to-DC converter 308 that has charge on it. In this case, the capacitor in the DC-to-DC converter 308 may discharge across the electrical load (e.g., the electrical device), thereby providing power to the electrical load even when the AC grid signal 302 is not passed to the AC-to-DC converter 306.

[0063] Control of Switch 310

[0064] It will be appreciated that the control of switch 310 by the signal processing and switch control circuitry 304 may be based on a determination by the signal processing circuitry of when the AC grid signal 302 is at a relatively low voltage ( / .e., far removed from its peak voltage value).

[0065] Signal Processing - Second circuit arrangement

[0066] It will be appreciated that one or more of the methods of determining when the AC grid signal 302 is at a low voltage ( / .e., far removed from its peak voltage value) that may be performed by the signal processing and switching circuitry 304 may be the same as the methods described above with reference to the signal processing and switch control circuitry 104.

[0067] Signal Processing - Further details

[0068] There now follows a further detailed description of the signal processing that may be performed by the signal processing and switch control circuitry 104 and / or the signal processing and switch control circuitry 304.

[0069] For example, having received the AC main signal 102, 302, the signal processing and switch control circuitry 104 / 304 may determine the regions / portions of the AC grid signal 102, 302 where it is at (or near) to its minimum and / or maximum voltage value. Based on that determination (using one of the methods described above), the signal processing and switch control circuitry 104 / 304may output two (or more) signals, (e.g., square wave signals) that indicate points in time that correspond to regions of the AC grid signal 102 that contains the maximum voltage value and / or the minimum voltage value. For example, Fig. 4a shows the same typical AC grid signal shown in Figure 2a and Fig. 4b depicts a square waveform 414 that is positive at the points in time that correspond to regions of the AC grid signal 102, 302 that contains a maximum voltage value, while Fig. 4c depicts a square waveform 416 that is positive at the points in time that correspond to regions of the AC grid signal 102, 302 that contains a minimum voltage value. Using both of those signals the signal processing and switch control circuitry 104 / 304 may then in turn determine periods where the voltage of the AC grid signal 102, 302 is close to its zero crossing points - as the times when both square waveforms 414 and 416 are at a low value. This would effectively generate the square waveform shown in Fig. 2b.

[0070] Having determined the times at which the AC grid signal 102 is close to the zero crossing points as shown in Fig. 2b previously, the signal processing and switch control circuitry 104 / 304 may then use the signal shown in Fig. 2b to determine when the switch 110, 310 should be open and when the switch 110, 310 should be closed.

[0071] Alternatively still, the signal processing and switch control circuitry 104 / 304 could directly use the square waveforms 414 and 416 to control the position of the switch 110 / 310. Specifically, the signal processing and switch control circuitry 104 / 304 could open the switch 110 / 310 when either of waveforms 414 or 416 are high and close the switch 110 / 310 at all other times.

[0072] DC-to-DC converters

[0073] As alluded to above, at the times when the switch 110 / 310 is open, the load 112, 312 across the output of the conversion circuitry 108 / 308 may be provided with sufficient amounts of power from a capacitor provided in the DC-to-DC converter 108 / 308 until the switch 110 / 310 is closed again.

[0074] There therefore now follows examples of DC-to-DC converters that may be implemented in the first and second circuit arrangements of Figs. 1 and 3.

[0075] Fig. 5a illustrates an example of a step-down DC-to-DC converter 500 that may be implemented in either of the first and second circuit arrangements of Figs. 1 and 3. The step-down converter is a type of DC-to-DC converter that has an output voltage magnitude that is less than the input voltage magnitude.

[0076] As shown in Fig. 5a, the step-down DC-to-DC converter 500 includes a voltage input Vm 502 which may, for example, be a high-voltage DC (HVDC) input that is received from an AC-to- DC converter (e.g., AC-to-DC converter 106, 306). The step-down DC-to-DC converter 500 also includes a switch 504, an inductor 506, a diode 508, and a capacitor 510.

[0077] While in the ‘on’ state i.e., when the switch 504 is closed, the input voltage Vm is directly connected to the inductor 506 causing a build-up of stored energy in the inductor 506. In this stage, the capacitor 510 supplies energy (DC power) to any load connected to the output Vout of the step-down DC-to-DC converter. On the other hand, while in the ‘off’ state i.e., when the switch 504 is open, the inductor 506 is connected to the output Vout of the circuit and thus any load that may be connected across the output of the step-down DC-to-DC converter. Additionally, the inductor 506 is connected to the capacitor 510, and thus energy (DC power) is provided to the load connected to the output Vout of the step-down DC-to-DC converter via the inductor 506 i.e., energy is transferred from the inductor 506 to the capacitor 510, and then to any load connected to the output Vout of the circuit.

[0078] Thus in the context of the circuit arrangements described above with reference to Figs. 1 and 3, it will be appreciated that when the switch 110 or 310 of those circuit arrangements is open, and thus no signal is provided to the step-down DC-to-DC converter, the capacitor 510 may supply energy (DC power) to any load connected to the output Vout of the step-down DC-to-DC converter.

[0079] Fig. 5b illustrates an example of a Buck-Boost DC-to-DC converter 500 that may be implemented in either of the first and second circuit arrangements of Figs. 1 and 3. The buck-boost converter is a type of DC-to-DC converter that has an output voltage magnitude that is either greater than or less than the input voltage magnitude.

[0080] As shown in Fig. 5b, the Buck-Boost DC-to-DC converter 600 includes a voltage input Vm 502 which may, for example, be a high-voltage DC (HVDC) input that is received from an AC-to-DC converter (e.g., AC-to-DC converter 106, 306). The Buck-Boost DC-to-DC converter 600 also includes a switch 504, an inductor 506, a diode 508, and a capacitor 510.

[0081] While in the ‘on’ state i.e., when the switch 504 is closed, the input voltage Vm is directly connected to the inductor 506 causing a build-up of stored energy in the inductor 506. In this stage, the capacitor 510 supplies energy (DC power) to any load connected to the output Vout of the Buck-Boost DC-to-DC converter.

[0082] On the other hand, while in the ‘off’ state i.e., when the switch 504 is open, the inductor 506 is connected to the output Vout of the circuit and thus any load that may be connected across the output of the Buck-Boost DC-to-DC converter. Additionally, the inductor 506 is connected to the capacitor 510, and thus energy (DC power) is provided to the any load connected to the output Vout of the Buck-Boost DC-to-DC converter via the inductor 506 i.e., energy is transferred from the inductor 506 to the capacitor 510, and then to any load connected to the output Vout of the circuit.

[0083] Thus in the context of the circuit arrangements described above with reference to Figs. 1 and 3, it will be appreciated that when the switch 110 or 310 of those circuit arrangements is open, and thus no signal is provided to the Buck-Boost DC-to-DC converter, the capacitor 510 may supply energy (DC power) to any load connected to the output Vout of the Buck- Boost DC-to-DC converter.

[0084] Alternatives & Modifications

[0085] Detailed examples have been described above. As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above examples whilst still benefiting from the concepts embodied therein.

[0086] The signal processing and switch control circuitry may comprise any suitable form of processing circuitry including (but not limited to), for example: one or more hardware implemented computer processors; microprocessors; central processing units (CPUs); arithmetic logic units (ALUs) processing registers; hardware or software implemented counters, pointers and / or timers; and / or the like. Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0087] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “containing,” means “including but not limited to,” and is not intended to (and does not) exclude other components, integers, or steps.

[0088] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

Claims

Claims1. Apparatus for converting an alternating current, AC, mains signal to a direct current, DC, signal for powering an electronic device, the apparatus comprising: means for receiving the AC mains signal; conversion circuitry for converting the AC mains signal or a signal derived from the AC mains signal into the DC signal for powering the electronic device; switching circuitry for receiving the AC mains signal or the signal derived from the AC mains signal and for selectively applying the AC mains signal or the signal derived from the AC mains signal to the conversion circuitry; and processing circuitry for processing the AC mains signal or the signal derived from the AC mains signal to determine periods of time in the vicinity of zero crossing points of the AC mains signal and configured to control the switching circuitry so that during said periods of time in the vicinity of said zero crossing points, the AC mains signal or the signal derived from the AC mains signal is applied to the conversion circuitry and so that during periods of time in the vicinity of peaks of the AC mains signal, the switching circuitry does not apply said AC mains signal or the signal derived from the AC mains signal to said conversion circuitry.

2. Apparatus according to claim 1, wherein the conversion circuitry comprises a capacitor that maintains the DC output from the conversion circuitry during periods of time when the AC mains signal or the signal derived from the mains signal is not applied to the conversion circuitry.

3. Apparatus according to claim 1 or 2, wherein the processing circuitry is configured to detect zero crossing points of the AC mains signal and is configured to determine said periods of time in the vicinity of zero crossing points of the AC mains signal using said crossing points and a timer.

4. Apparatus according to claim 1 or 2, wherein the processing circuitry is configured to determine periods of time in the vicinity of said peaks of the AC mains signal or the signal derived from the AC mains signal and is configured to determine said periods of time in the vicinity of said zero crossing points using the determined periods of time in the vicinity of said peaks of the AC mains signal or the signal derived from the AC mains signal.

5. Apparatus according to claim 1 or 2, wherein the processing circuitry is configured to determine said periods of time in the vicinity of zero crossing points of the AC mains signalby comparing the AC mains signal or the signal derived from the AC mains signal with a threshold.

6. Apparatus according to claim 5, wherein the processing circuitry is configured to determine said periods of time in the vicinity of zero crossing points of the AC mains signal when the AC mains signal or the signal derived from the AC mains signal is below said threshold.

7. Apparatus according to any preceding claim, wherein the processing circuitry is formed from analogue circuit components.

8. Apparatus according to claim 7 when dependent on claim 5, wherein the processing circuitry is configured to compare the AC mains signal or the signal derived from the AC mains signal with a threshold by applying the AC mains signal or the signal derived from the AC mains signal to a filter circuit defining said threshold.

9. Apparatus according to any of claims 1 to 6, wherein the processing circuitry comprises digital signal processing circuitry.

10. Apparatus according to claim 9, wherein the digital signal processing circuitry is configured to use a frequency transform processing technique to generate a digital representation of the AC mains signal and is configured to determine said periods of time in the vicinity of the zero crossing points of the AC mains signal using said digital representation of the AC mains signal.

11. Apparatus according to any preceding claim, wherein the apparatus comprises rectifier circuitry for rectifying the AC mains signal to generate a rectified signal corresponding to said signal derived from the AC mains signal.

12. Apparatus according to claim 11 , wherein said processing circuitry is configured to receive the AC mains signal and wherein the switching circuitry is configured to receive the rectified signal from the rectifier circuitry and to pass the rectified signal to the conversion circuitry during said periods of time in the vicinity of the zero crossing points of the AC mains signal.

13. Apparatus according to claim 11 , wherein said processing circuitry is configured to receive the rectified signal from the rectifier circuitry and wherein the switching circuitry isconfigured to receive the rectified signal from the rectifier circuitry and to pass the rectified signal to the conversion circuitry during said periods of time in the vicinity of the zero crossing points of the AC mains signal.

14. Apparatus according to any of claims 1 to 10, wherein said processing circuitry is configured to receive the AC mains signal and wherein the switching circuitry is configured to receive the AC mains signal and to pass the AC mains signal to the conversion circuitry during said periods of time in the vicinity of the zero crossing points of the AC mains signal.

15. Apparatus according to any preceding claim, wherein said conversion circuitry comprises DC to DC conversion circuitry.

16. Apparatus according to any preceding claim, wherein said conversion circuitry comprises AC to DC conversion circuitry.

17. A method for converting an alternating current, AC, mains signal to a direct current, DC, signal for powering an electronic device, the method comprising: receiving the AC mains signal; using conversion circuitry to convert the AC mains signal or a signal derived from the AC mains signal into the DC signal for powering the electronic device; using switching circuitry to receive the AC mains signal or the signal derived from the AC mains signal and to selectively apply the AC mains signal or the signal derived from the AC mains signal to the conversion circuitry; and processing the AC mains signal or the signal derived from the AC mains signal to determine periods of time in the vicinity of zero crossing points of the AC mains signal, to control the switching circuitry so that during said periods of time in the vicinity of said zero crossing points, the AC mains signal or the signal derived from the AC mains signal is applied to the conversion circuitry and so that during periods of time in the vicinity of peaks of the AC mains signal, the switching circuitry does not apply said AC mains signal or the signal derived from the AC mains signal to said conversion circuitry.

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