Electrical conversion circuitry

Abstract

A DC signal for powering a load is generated from a rectified AC signal. Conversion circuitry is controlled to convert the received rectified AC signal into a selected one of a plurality of different

Description

The present invention relates to a method and apparatus / circuitry for use in the conversion of an AC grid (or mains) signal to a DC signal suitable for use by a load. The invention has particular although not exclusive relevance to a power conversion circuit that can provide power to a controller that controls DC-to-DC conversion circuitry that can provide different DC voltages and powers to the load. Typically, in AC-to-DC power conversion systems a bridge rectifier 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 to reduce the variation of the generated HVDC signal. For a 240V mains (AC) signal the resulting HVDC signal may up to about 120V (DC). To reduce the output voltage level, flyback converter, a step-down DC-to-DC converter, a Buck-Boost DC-to-DC converter, or the like, may be provided after the rectifying and smoothing circuitry to bring the DC voltage down to the voltage required by the load (which typically is somewhere in the range of 3 volts and 40 volts (DC) although higher voltages can of course be output). Typically, the DC-to-DC converter circuitry is controlled via a controller that operates a switch of the DC-to-DC converter circuitry in order to charge (and discharge) a capacitor of the DC-to-DC converter circuitry to produce a constant DC power output to a load connected to the DC-to-DC converter circuitry. With the development of modern power conversion circuitry such as the Universal Serial Bus-C (USB-C) technology, loads having different voltage and power requirements can be connected to the same power conversion circuitry. This has caused such power conversion circuitry to become more complex as it must be able to supply the required voltage level and power requirement for the different loads. A further complexity is that modern converter circuits need to minimise their standby power losses when the load is either not connected or not drawing much power. There is therefore a need to develop improved conversion circuits and parts thereof. Summary of Invention Embodiments of the invention provide apparatus for generating a DC signal for powering a load. The apparatus comprises: means for receiving a rectified AC signal; conversion circuitry capable of converting the received rectified AC signal into one of a plurality of different DC outputs for powering a load; control circuitry for controlling the conversion circuitry to cause the conversion circuitry to convert the received rectified AC signal into a selected one of the plurality of different DC outputs in accordance with a requirement of the load; and auxiliary power circuitry configured to convert the rectified AC signal into an auxiliary DC signal for powering the control circuitry. In the apparatus for generating a DC signal for powering a load, the auxiliary power circuitry may be connected in parallel with the conversion circuitry. In the apparatus for generating a DC signal for powering a load, the auxiliary power circuitry may comprise sub-circuitry. For example, the auxiliary power circuitry may comprise DC voltage levelling circuitry. That DC voltage levelling circuitry may be configured to In the apparatus for generating a DC signal for powering a load, the auxiliary power circuitry may be configured to charge a first capacitor during each cycle of the rectified AC signal to provide a smoothed rectified AC signal. That the smoothed rectified AC signal may be input to the conversion circuitry. In the apparatus for generating a DC signal for powering a load, the voltage stored on the first capacitor of the auxiliary power circuitry may be within the range of 100 volts to 250 volts. Furthermore, the first capacitor of the auxiliary power circuitry may be charged through a first inductor of the auxiliary power circuitry and the charging of that first capacitor may controlled by opening and closing a switch whilst the rectified AC signal is greater than a voltage stored on the first capacitor. The first inductor of the auxiliary power circuitry through which the first capacitor may be charged may be coupled to a second inductor of the auxiliary power circuitry so that during switching of the switch current flowing in the first inductor induces a voltage in the second inductor. Additionally, a diode and a second capacitor of the auxiliary power circuitry may be connected to the second inductor in such a way as to prevent current flow in the second inductor when the switch is closed to charge the first capacitor and to allow current to flow to charge the second capacitor when the switch is opened. In the apparatus for generating a DC signal for powering a load, the voltage stored on the second capacitor may provide the auxiliary DC signal for powering the control circuitry, and the voltage stored on that second capacitor may be, by way of example only, within the range of 3 volts to 25 volts. Nevertheless, it will be appreciated that the voltage stored on the second capacitor may be any voltage that is sufficiently large enough to provide power to the control circuitry, more especially when the switch of the auxiliary power circuitry is open. In the apparatus for generating a DC signal for powering a load, the charging of the first capacitor may be controlled by opening and closing the switch whilst the rectified AC signal is greater than a voltage stored on the first capacitor at a frequency of between 10 kHz and 1 MHz. In the apparatus for generating a DC signal for powering a load, the auxiliary DC signal for powering the control circuitry may be substantially independent of the selected one of the plurality of different DC outputs. That is to say the auxiliary power circuit and the conversion circuitry of the apparatus may be arranged so that the power drawn by the load has a negligible effect on the operation of the auxiliary power circuit thereby ensuring that a substantially constant DC signal can be provided to the control circuitry. The apparatus for generating a DC signal for powering a load may also comprise rectification circuitry for generating the rectified AC signal from an input AC signal. For example, the apparatus may comprise any appropraite rectifier such as, by way of example only, a half wave rectifier, a full wave rectifier, a bridge rectifier, or the like. The load connected to the apparatus for generating a DC signal for powering that load may be any appropriate electronic device, however more particularly, it may be a Universal Serial Bus type C (USB-C) electronic device. Embodiments of the invention also provide a method for generating a DC signal for powering a load. The method comprises negotiating power requirements of the load; receiving a rectified AC signal; controlling, by control circuitry, conversion circuitry to cause the conversion circuitry to convert the rectified AC signal into a selected one of a plurality of different DC outputs for powering a load in accordance with the negotiated power requirement of the load; and converting the rectified AC signal into an auxiliary DC signal for powering the control circuitry. Brief Description of Figures Examples of the electrical conversion circuitry and its various elements, along with methods of operating the electrical conversion circuitry will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 schematically illustrates an electrical conversion circuit; Figure 2 illustrates an example of a rectified voltage applied across a smoothing capacitor used in the electrical conversion circuit shown in Figure 1 during charging and discharging of the capacitor; Figure 3a illustrates an example of a current flowing through the third inductor as the second switch is opened / closed; Figure 3b illustrates an example voltage (potential difference) across the windings of the third inductor as the second switch is opened / closed; and Figure 4 illustrates a simplified sequence diagram of a method of controlling the provision of power to the load of the electrical conversion circuit of Figure 1. Overview Figure 1 illustrates an example of electrical conversion circuitry 100 for converting an AC grid signal 102 from an AC source 104 to a DC signal 106 suitable for a load 108 connected to the circuitry 100 (e.g., a USB-C power delivery device, or the like). The electrical conversion circuitry 100 includes rectifier circuitry 110 to rectify the AC grid signal 102 to produce a rectified signal 111 output by the rectifier circuitry at output 110-1. The rectifier circuitry 110 may take the form of any appropriate rectifier circuitry known to the skilled person. The electrical conversion circuitry 100 also has appropriate DC-to-DC conversion circuitry 114 (e.g., a flyback converter, or the like) for converting the rectified signal 111 output by the rectifier circuitry 110, to provide a smoothed output DC signal 106 at a voltage level and power level suitable for the load 108. The DC-to-DC conversion circuitry 114 includes a first inductor 116-1 having one end 116-11 that is connected to the output 110-1 of the rectifier circuitry 110 to receive the rectified signal 112. The other end 116-12 of the first inductor 116-1 is connected in series through a first switch 118 to a reference voltage (e.g. ground). The switch 118 is controlled by a main controller 120 via an appropriate control signal 122 to control the current flowthrough the first inductor 116-1. A second inductor 116-2 is coupled to the first inductor 116-1 such that when a current flows through the first inductor 116-1 a voltage (EMF) is induced in the second inductor 116-2. The second inductor 116-2 is connected to a diode 128 and a first capacitor 132 and the load 108 is connected across the first capacitor 132. The voltage induced in the second inductor 116-2 causes a current to flow in the secondary circuit formed by the second inductor 116-2, the diode 128 and the capacitor 132. By varying the timing and duration that the switch 118 is opened and closed relative to the rectified signal 111 output from the rectifier circuitry 110, the main controller 120 can control the voltage and power available to the load 108 through the inductors 116-1 and 116-2 and the diode 128 and capacitor 132. The main controller 120 receives a voltage and power demand signal 123 from the load 108 - indicating the voltage and power level required by the load 108. Based on this signal 123, the main controller 120 controls the opening and closing of the switch 118 to provide the required voltage and power to the load 108. The DC-to-DC conversion circuitry 114 is just one example of such circuitry and other types of DC-DC conversion circuitry 114 can be used. A problem arises with such DC-DC conversion circuitry 114 when such circuitry is required to supply a wide range of voltages and power levels to different loads 108. In particular, the main controller 120 is normally powered using the DC voltage output by the DC-DC conversion circuitry 114. However, when the output is designed to produce a wide range of output voltages (as is the case for USB-C devices), it is not practical to use the DC output from the DC-DC converter circuitry 114. Specifically, the main controller 120 needs a fixed voltage level to operate and if this voltage level is different from the voltage generated by the DC-DC conversion circuitry 114, then inefficient and complex circuitry is needed to generate the required voltage from the variable DC output from the DC-DC conversion circuitry 114. To address or at least ameliorate this problem, the inventors have provided auxiliary power circuitry 126 that is configured to provide the required constant operating voltage to the main controller 120 irrespective of the instantaneous voltage level of the rectified signal 112 or the variable DC voltage level supplied to the load 108 by the DC-DC conversion circuitry 114. As shown in Figure 1, the auxiliary power circuitry 126 includes appropriate DC voltage levelling circuitry 127 for smoothing / levelling off the rectified signal 111 output by the rectifier circuitry 110, to provide a smoothed I levelled output DC signal 112 to the DC-DC conversion circuitry 114. The DC voltage levelling circuitry 127 for smoothing out the rectified signal 111 output by the rectifier circuitry 110 includes a second diode 140, a switch 136, a third inductor 116-3, a second capacitor 138, and a fourth diode 142. The second diode 140 and second switch 136 are connected in series between the output 110-1 of the rectifier circuitry 110 and a reference voltage (e.g. ground), with the second diode 140 blocking current flow from the output 110-1 of the rectifier circuitry 110 to ground when the second switch 136 is closed. The second capacitor 138 and the third diode 142 are also connected in series between the output 110-1 of the rectifier circuitry 110 and a reference voltage (e.g. ground), with the third diode 142 blocking current flow from the output 110-1 of the rectifier circuitry 110 to the second capacitor 138. The third inductor 116-3 is connected between the output of the second switch 136 and the second capacitor 138 to allow charging of the second capacitor 138 when the second switch 136 is closed. As shown in Figure 1, the opening and closing of the second switch 136 is controlled via a control signal 152 received from the control circuitry 150. That control circuitry 150 may, for example, via the control signal 152, control the second switch 136 to open and close repeatably at a specified high frequency (e.g., at a frequency of multiple kHz, for example: 45 kHz or 125 kHz)) to control the flow of current through the third inductor 116-3 and charge up the second capacitor 138. As also shown in Figure 1, the auxiliary power circuitry 126 also includes a fourth inductor 116-4 that is coupled to the third inductor 116-3 such that when current flows through the third inductor 116-3 a voltage (EMF) is induced in the fourth inductor 116-4. That fourth inductor 116-4 is connected to a fourth diode 144 and to a third capacitor 146. The third and fourth inductors 116-3 and 116-4 form a step down transformer to reduce the high voltage DC signal stored on the second capacitor 138 to a much lower DC voltage (e.g. between 3 V to 10 V) suitable for powering the main controller 120 via the power input line 124. It will be appreciated that the control circuitry 150 may also be powered by the low voltage power signal 148 generated by the auxiliary power circuitry 126. As will be described in more detail below, during operation of the electrical conversion circuitry 100, the AC grid signal 102 is passed through rectifier circuitry 110 to rectify the AC grid signal 102 and output, at the output 110-1 of the rectifier circuitry 100, a rectified (e.g., high-voltage DC (HVDC)) signal 111. That rectified signal 111 is then passed to the DC voltage levelling circuitry 127 for smoothing out the rectified signal 111 to produce a smoothed HVDC signal 112. More specifically, during operation, when the second switch 136 of the DC voltage levelling circuitry 127 is closed, the rectified signal 111 from the rectifier circuitry 110 passes through the third inductor 116-3 and charges the second capacitor 138. When the second switch 136 of the DC voltage levelling circuitry 127 is opened, the second capacitor 138 can discharge to provide the smoothed HVDC signal 112 to an input 134 of the DC-to DC converter circuitry 114 to maintain a generally constant power to the DC-to DC converter circuitry 114 for subsequent conversion and provision to the load 108. The period during which the second capacitor 138 can be charged starts when the voltage of the rectified signal 111 from the rectifier circuitry 110 goes above a certain voltage and the period during which the second capacitor 138 can be charged ends when the rectified signal 111 from the rectifier circuitry 110 drops below another voltage. In this way, the DC voltage levelling circuitry 127 can smooth I level-out the DC voltage by storing energy in the second capacitor 138 when the voltage of the rectified signal 111 peaks and can return that energy from the second capacitor 138 when the voltage of the rectified signal 111 drops below that stored on the second capacitor 138. Beneficially, by controlling the charging and discharging of the second capacitor 138 in this manner, the efficiency of the AC-to-DC electrical conversion can be improved compared to that achieved with typical electrical conversion circuits. For example controlling the charging and discharging of the second capacitor 138 in this manner allows, i) Control of the charging on / off times of the capacitor 141 to adjust the smoothness of the smoothed I levelled output DC signal 112; and / or ii) Control of the total charging period of the second capacitor 138 to account for the power being drawn by the load 108 across the electrical conversion circuitry 100. Furthermore, during operation of the electrical conversion circuitry 100, when the second switch 136 is closed in response to the control signal 152 received from the control circuitry 150 and the rectified signal 111 from the rectifier circuitry 110 passes through the third inductor 116-3 to the second capacitor 138 to charge up that second capacitor 138, due to the orientation of the windings of the third inductor 116-3 and the fourth inductor 116-4, and the presence of the fourth diode 144 no current will flowthrough the fourth inductor 116-4 during this charging period. When the second switch 136 is opened in response to the control signal 152, and the second capacitor 138 begins to discharge through the third diode 142 to provide the smoothed HVDC signal 112 to an input 134 of the DC-to DC converter circuitry 114, the current flowing through the third inductor 116-3 will reduce to zero and this changing current through the third inductor 116-3 induces a voltage (EMF) in the fourth inductor 116-4, which in turn causes a corresponding electrical current / 2 to flow and charge up the third capacitor 146. That electrical current / 2 also flows through the power input line 124 to the main controller 120 to power that main controller 120 until the second switch 136 is closed again in response to the control signal 152 from the control circuitry 150, at which point the charge on the third capacitor 146 will begin to discharge to provide a flow of current to the main controller 120 through the power input line 124 to power that main controller 120 until the second switch 136 is opened again. Thus a much lower constant DC voltage (e.g. between 3V to 25V) 148 suitable for powering the main controller 120 can be provided to the main control 120 via the power input line 124 irrespective ofwhetherornotthe second switch 136 is open or closed. It will be appreciated that the voltage stored on the capacitor 138, the turns ratio of the third and fourth inductors and the size of the fourth capacitor 146, as well as the switching periods of the switch 136 are chosen to provide the desired substantially constant voltage on the fourth capacitor 146 that can power the Main controller 120 as well as the control circuitry 150. Beneficially, by providing a separate auxiliary power supply circuit 126 as shown in Fig. 1, a constant low DC voltage can be provided to the main controller 120 to power the main controller 120 irrespective of the varying rectified signal 111, and irrespective of desired voltage level required by the load 108. This in turn advantageously means that: i) The risk of high voltages being provided to the main controller 120 by the DC-to-DC converter 114 when the load 108 negotiates such a high voltage is avoided, thereby preventing damage to the main controller 120. ii) No complex or inefficient circuitry is needed to convert the variable DC voltage supplied to the load 108 to a suitable value for the main controller 120 or the control circuitry 150. The above overview is given to introduce the main circuit components used in the conversion circuitry. Amore detailed description of how the conversion circuitry 100, and in particular the auxiliary power circuitry 126, operate will now be given. Figure 2 is a graphical representation illustrating the rectified signal 111 output by the rectifier circuitry 110 and the desired timings of when charging of the third capacitor 146 is to start and when charging of the third capacitor 146 is to end or stop during each cycle of the rectified signal 111. More specifically, the control circuitry 150 starts to charge the second capacitor 138 at time tcs (or normalised time cotes as shown in Figure 2) when the instantaneous voltage level of the rectified signal 111 is greater than the voltage stored on the second capacitor 138, and stops charging the second capacitor 138 at time tee (or normalised time cotcE as shown in Figure 2) when the voltage on the second capacitor 138 has reached the desired voltage level. For example, the control circuitry 150 may stop charging the second capacitor at a time tcE when the voltage on the second capacitor 138 has received a value of between 100 to 250 V. The control circuitry 150 performs a similar charging process during each cycle of the rectified signal 111. During each charging period, the control circuitry 150 rapidly opens and closes the second switch 136 at a high frequency of between about 10 kHz and 1 MHz. By switching the second switch 136 in this way, the second capacitor 138 may be charged in small bursts over a period of time, which helps to minimise losses in the inductor 116-3 and helps to smooth out the rate at which the charge builds up on the plates of the second capacitor 138. Further, if the control circuitry 150 just closed the switch once per cycle of the rectified signal 111, then the third capacitor 146 would not receive sufficient charge to be able to power the main controller 120 and the control circuitry 150. However, since the control circuitry 150 opens and closes the second switch 136 rapidly during the charging time period (T1 shown in Figure 2), each time the switch 136 is opened, a small amount of charge is stored onto the capacitor 146. Over the course of the charging period (T1 shown in Figure 2), the third capacitor 146 is charged sufficiently to be able to provide the power needed by the main controller 120 and the control circuitry 150 until the next charging period begins. Thus, the charge stored on the third capacitor 146 during the charging period T1 is sufficient to allow the third capacitor 146 to power the main controller 120 and the control circuitry 150 during the non-charging period T2 when the second switch 136 remains open. When the instantaneous voltage level of the rectified signal 111 output from the rectifier circuit 110 drops below the voltage stored on the capacitor 138, the voltage on second the capacitor 138 will be provided back to the input line 134 which then feeds into the DC-DC conversion circuitry 114. As those skilled in the art will appreciate, the switching frequency used to open and close the second switch 136 is set to ensure that the charge stored on the third capacitor 146 is sufficient to meet the power requirements of the main controller 120 and the control circuitry 150. If the power requirements of the main controller 120 or of the control circuitry 150 changes, then the control circuitry 150 may vary the switching frequency accordingly. Figure 3a is a graphical representation illustrating an example current that flows through the third inductor 116-3 as the second switch 136 is opened / closed. As shown in Figure 3a, when the second switch 136 of the DC voltage levelling circuitry 127 is closed during the charging period of the second capacitor 138 ( / .e. during the rapid switching of that second switch 136 at a high frequency of between about 10 kHz and 1 MHz), the rectified signal 111 from the rectifier circuitry 110 passes through the third inductor 116-3, causing an increasing current to flow through the third inductor until the second switch 136 is closed. As that current flows through the third inductor 116-3, the second capacitor 138 is charged up. When the second switch 136 of the DC voltage levelling circuitry 127 is open during the charging period of the second capacitor 138 ( / .e. during the rapid switching of that second switch 136 at a high frequency of between about 10 kHz and 1 MHz), the second capacitor 138 begins to discharge through the third diode 142 to provide the smoothed HVDC signal 112 to an input 134 of the DC-to DC converter circuitry 114, and the current flowing through the third inductor 116-3 will reduce backdown to zero. As described above, as the current flowing through the third inductor 116-3 reduces back down to zero, a voltage (EMF) is induced in the fourth inductor 116-4, which in turn causes the corresponding electrical current / 2 to flow and charge up the third capacitor 146. As shown in Figure 3a, the rate of change of the current flowing through the third inductor 116-3 when the second switch 136 is opened may be greater than the rate of change of the current flowing through the third inductor 116-3 when the second switch 136 is closed. Figure 3b is a graphical representation illustrating an example voltage across the windings of the third inductor 116-3 as the second switch 136 is opened / closed. As shown in Figure 3b, when the second switch 136 of the DC voltage levelling circuitry 127 is closed during the charging period of the second capacitor 138 ( / .e. during the rapid switching of that second switch 136 at a high frequency of between about 10 kHz and 1 MHz) and a current flows through the third inductor 116-3 to the second capacitor 138, a potential difference is induced across the windings of the third inductor 116-3 that has a value of Vac - Vc where Vac is the voltage of the rectified signal 111 and the voltage across the second capacitor 138. As will be appreciated, the value of Vac - Vc may vary depending on the value of Vac at any given time during the charging period. When the second switch 136 of the DC voltage levelling circuitry 127 is open during the charging period of the second capacitor 138 ( / .e. during the rapid switching of that second switch 136 at a high frequency of between about 10 kHz and 1 MHz) and the second capacitor 138 begins to discharge through the third diode 142, the potential difference across the windings of the third inductor 116-3 has a value -Vc. An example methods 400 of operating the electrical conversion circuitry 100 will now be described with reference to Figure 4. Electrical Conversion Circuitry: Method of Operation Figure 4 illustrates a simplified sequence diagram of a method of controlling the provision of power to the load 108 of the electrical conversion circuit of Figure 1. In particular the method 400 allows for the control of the charging and discharging of the first capacitor 132 of the electrical conversion circuit 100 so as to provide a negotiated voltage and power to the load 108. At step S402, in accordance with the USB-C standard, and in response to a load 108 being placed across the electrical conversion circuit 100, the main controller 120 communicates with the load 108 to negotiate the voltage and power requirements of the load 108. For example, via an appropriate interface, the load 108 negotiates with the main controller 120 and chooses an appropriate voltage and power level that is necessary to meet the needs of the load 108 and which can be reliably and safely supplied by the electrical conversion circuit 100. At step S404, the main controller 120, in response to the negotiated voltage and power level, controls, via appropriate control signals 122, the opening and closing of the first switch 118 to provide the negotiated voltage and power to the load 108. In particular, the main controller 120 may determine a start time and a stop time of a charging period for charging the first capacitor 132 that will ensure sufficient charging of the first capacitor 132 to provide the appropriate voltage and power requested by the load 108. The main controller 120 may also rapidly open and close the first switch 118 at a high frequency of between about 10 kHz and 1 MHz. By switching the first switch 118 in this way, the capacitor 138 may be charged in small bursts over a period of time, which helps to minimise losses in the inductors 116-1 and 116-2 and helps to smooth out the rate at which the charge builds up on the plates of the first capacitor 132. Alternatives & Modifications 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. The main controller 120 and / or the control circuitry 150 may comprise any suitable form of control 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. Whilst it is described above that the main controller 120 and the control circuitry 150 are described as being two separate entities, it will be appreciated that the functionalities of these two controllers may be provided by a single controller or control circuitry. Whilst the electrical conversion circuitry 100 of Figure 1 includes a DC voltage levelling circuitry 127 that comprises two diodes, one switch, an inductor, and a single capacitor, it will nevertheless be appreciated that appropriate adaptations to that DC voltage levelling circuitry 127 may be made to further improve the smoothing out of the rectified DC signal 111 received from the rectifier circuit 110. For example, the DC voltage levelling circuitry 127 may include additional capacitors and / or resistors to further smooth out the rectified DC signal 111 such as in a pi-filter. 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. Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

Claims

1. Apparatus for generating a DC signal for powering a load, the apparatus comprising:means for receiving a rectified AC signal;conversion circuitry capable of converting the received rectified AC signal into one of a plurality of different DC outputs for powering a load;control circuitry for controlling the conversion circuitry to cause the conversion circuitry to convert the received rectified AC signal into a selected one of the plurality of different DC outputs in accordance with a requirement of the load; andauxiliary power circuitry configured to convert the rectified AC signal into an auxiliary DC signal for powering the control circuitry.

2. The apparatus of claim 1, wherein the auxiliary power circuitry is connected in parallel with the conversion circuitry.

3. The apparatus of claim 1 or claim 2, wherein the auxiliary power circuitry is configured to charge a first capacitor during each cycle of the rectified AC signal to provide a smoothed rectified AC signal.

4. The apparatus of claim 3, wherein the smoothed rectified AC signal is input to the conversion circuitry.

5. The apparatus of claim 3 or claim 4, wherein the voltage stored on the first capacitor is within the range of 100 volts to 250 volts6. The apparatus of any one of claims 3 to 5, wherein the first capacitor is charged through a first inductor, and wherein charging of the first capacitor is controlled by opening and closing a switch whilst the rectified AC signal is greater than a voltage stored on the first capacitor.

7. The apparatus of claim 6, wherein the first capacitor is connected to the first inductor and, wherein a second inductor is coupled to the first inductor so that during switching of the switch current flowing in the first inductor induces a voltage in the second inductor.

8. The apparatus of claim 7, wherein a diode and a second capacitor are connected to the second inductor, wherein the diode is connected to the second inductor to prevent current flow in the second inductor when the switch is closed to charge the first capacitor and to allow current to flow to charge the second capacitor when the switch is opened.

9. The apparatus of claim 8, wherein the voltage stored on the second capacitor provides the auxiliary DC signal for powering the control circuitry.

10. The apparatus of claim 8 or claim 9, wherein the voltage stored on the second capacitor is within the range of 3 volts to 25 volts.

11. The apparatus of any one of claims 6 to 10, wherein charging of the first capacitor is controlled by opening and closing the switch whilst the rectified AC signal is greater than a voltage stored on the first capacitor at a frequency of between 10 kHz and 1 MHz.

12. The apparatus of any preceding claim, wherein the auxiliary DC signal is substantially independent of the selected one of the plurality of different DC outputs.

13. The apparatus of any preceding claim, wherein the auxiliary power circuit and the conversion circuitry are arranged so that the power drawn by the load has a negligible effect on the operation of the auxiliary power circuit.

14. The apparatus of any preceding claim, further comprising:rectification circuitry for generating the rectified AC signal from an input AC signal.

15. The apparatus of any preceding claim, wherein the load to be powered is a Universal Serial Bus type C, USB-C, electronic device.

16. A method for generating a DC signal for powering a load comprising:negotiating power requirements of the load;receiving a rectified AC signal;controlling, by control circuitry, conversion circuitry to cause the conversion circuitry to convert the rectified AC signal into a selected one of a plurality of different DC outputs for powering a load in accordance with the negotiated power requirement of the load; andconverting the rectified AC signal into an auxiliary DC signal for powering the control circuitry.

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