Power supply circuit for an electricity meter

Abstract

A power supply circuit for use in an electricity meter is disclosed. The power supply circuit comprises a rectifier circuit, an oscillator circuit, and an isolation capacitor. The rectifier circuit is configured to rectify an oscillating signal received from the oscillator circuit, via the isolation capacitor, and to provide power to a further circuit that is isolated from a secondary-side power supply to the oscillator circuit. An electricity meter comprising the power supply circuit is also disclosed.

Description

[0001] POWER SUPPLY CIRCUIT FOR AN ELECTRICITY METER

[0002] FIELD OF INVENTION

[0003] The present disclosure is in the field of power supply circuits, and relates in particular to power supply circuits for use in electricity meters, such as multi-phase electricity meters. Specifically, the present disclosure relates to a high efficiency and low- cost means of powering circuitry that is floating on phase voltage and isolated from a circuit providing power to the circuitry.

[0004] BACKGROUND TO INVENTION

[0005] Electricity meters, such as multi-phase electricity meters, may be provided for metering, e.g. measuring, consumption of electric power at domestic, commercial and / or industrial premises.

[0006] Such electricity meters may comprise circuity for metering current and / or voltage characteristics of one or more phases of an electrical power supply. Such electricity meters may be configured to communicate and / or store data corresponding to such characteristics. For example, one or more current sensors may be implemented for sensing a flow of current through a supply line, and measurement circuitry, such as an analog-to-digital converter or the like may be provided to accurately sense an output from the current sensors, or through an associated shunt.

[0007] Such measurement circuitry may be isolated from the supply line and / or further circuitry within the electricity meter, and may therefore be effectively floating relative to the supply line and / or further circuitry.

[0008] In one example of a known electricity meter, such floating circuits may typically be powered from supply line voltages with capacitive droppers implemented to generate a low voltage, and may work only at every half line cycle. Thus, this kind of power supply may exhibit a very low efficiency and may require a relatively large X-class capacitor to provide sufficient current to the floating circuit.

[0009] Furthermore, the X-class capacitor need to be implemented with sufficient capacity such that operation is guaranteed at the lowest possible line voltage, which may detrimentally increase losses when operating at a nominal operating voltage.

[0010] Furthermore, a relatively large capacitor may also mean that a apparent power consumption of the electricity meter is relatively large, wherein such apparent power consumption may not be chargeable to a consumer and may thus contribute to a financial loss to the electrical power supplier.

[0011] It is therefore desirable to provide a low cost, efficient means of powering circuitry that is floating on phase voltage and is electrically isolated from a circuit providing power to the circuitry.

[0012] It is therefore an aim of at least one embodiment of at least one aspect of the present disclosure to obviate or at least mitigate at least one of the above identified shortcomings of the prior art.

[0013] SUMMARY OF INVENTION

[0014] The present disclosure is in the field of power supply circuits for use in electricity meters, such as multi-phase electricity meters. According to first aspect of the disclosure, there is provided a power supply circuit for use in an electricity meter. The power supply circuit comprises: a rectifier circuit; an oscillator circuit; and an isolation capacitor. The rectifier circuit is configured to rectify an oscillating signal received from the oscillator circuit, via the isolation capacitor, and to provide power to a further circuit that is isolated from a secondary-side power supply to the oscillator circuit.

[0015] Advantageously, in such a circuit the rectifier and further circuit (which collectively may be referred to herein as a ‘floating part’ or ‘floating circuit’) may be powered from the isolated secondary-side power supply. The secondary side, e.g. circuitry that is isolated from a high-voltage line-side, may typically be powered separately with a floating output flyback power supply. Thus, the secondary-side power supply is already of high efficiency, and that output is fed to the floating circuit through the isolation capacitor. As such, an efficiency of the overall power supply to the rectifier circuit ad to the further circuit may be relatively improved.

[0016] The secondary-side power supply to the oscillator circuit may be configured to be electrically isolated from a line and / or load side of the electricity meter.

[0017] The power supply circuit may comprise the further circuit. The further circuit may comprise at least one analog-to-digital converter (ADC) configured to sense a current and / or voltage corresponding to a / the line and / or load side of the electricity meter.

[0018] For example, one or more shunt resistors may be implemented, wherein said ADC may be configured to sense a voltage drop across said shunt resistor. The further circuit may be isolated from the secondary-side power supply to the oscillator circuit by an isolation barrier. The isolation barrier may comprise at least one of: one or more capacitors; a digital isolator integrated circuit (IC); an optocoupler.

[0019] The rectifier circuit may comprise a rectifier for rectifying the oscillating signal received from the oscillator circuit.

[0020] The rectifier circuit may comprise at least one voltage regulator configured to receive a rectified voltage from the rectifier and to provide a regulated voltage to the further circuit.

[0021] For example, the regulator may provide a 12 Volt (V), a 5 V, a 3.3 V or the like reference to the further circuit.

[0022] A capacitance of the isolation capacitor may be selected to present a relatively high impedance to frequency components of 60 Hz or less on the oscillating signal from the oscillator circuit.

[0023] A capacitance of the isolation capacitor may be selected to present a relatively low impedance to frequency components of 1 kHz or greater on the oscillating signal from the oscillator circuit, such that a supply of current is provided from the oscillator circuit to the rectifier circuit.

[0024] The oscillator circuit may be configured to generate the oscillating signal having a frequency of at least 100 kHz. In some examples, the oscillator circuit may be configured to generate the oscillating signal having a frequency of at least 250 kHz.

[0025] That is, in the disclosed power supply circuit, the floating circuit may be fed with current from the secondary side through a relatively small isolation capacitor (relative to a typical X-class capacitor) using a relatively high frequency, which may be in the region of hundreds of kilohertz to low megahertz range. This relatively small isolation capacitor, which may have a capacitance in the range of nanofarads, may presents a high impedance at low frequencies like 50 or 60 Hz that are typically used on the line side of the electricity meter. However, at the high frequencies mentioned, the isolation capacitor may present a relatively low impedance and thus may supply current to the rectifier circuit, e.g. the floating circuit.

[0026] The oscillator circuit may comprise a driver. In some example embodiments, the driver may comprise a half bridge or a totem pole transistor. In some example embodiments, the driver may comprise an operational amplifier, a comparator, a motor driver IC, or a H-bridge.

[0027] That is, the isolation capacitor may be driven with a half bridge or one or more totem pole transistors from a secondary-side voltage, for example 12V. The secondary-side power supply to the oscillator circuit may comprise a floating output flyback power supply.

[0028] The secondary-side power supply to the oscillator circuit may comprise a floating output switch-mode power supply.

[0029] The secondary-side power supply to the oscillator circuit may be protected by a line-filtering capacitor and at least one of a voltage limiting resistor and a varistor.

[0030] The line-filtering capacitor may be configured to be connected between a / the line side and a neutral of the electricity meter. The line side may be at a substantially same potential as the rectifier circuit, e.g. a power supply to the rectifier circuit.

[0031] The power supply to the oscillator circuit may be referenced to one of: neutral; a rectified negative line voltage; or a rectified positive line voltage.

[0032] That is, the secondary side may be referenced to neutral, rectified negative line voltage or rectified positive line voltage. Each of these references may provide different arrangements for powering the floating circuit. For example, when referenced to neutral, current may flow from the secondary side to the floating circuit only when line voltage at the floating circuit is lower than the neutral, i.e., every half cycle of line voltage.

[0033] The power supply circuit may comprise a plurality of rectifier circuits. Each rectifier circuit may be configured to rectify an oscillating signal received from the oscillator circuit via a respective isolation capacitor. Each rectifier circuit may be configured to provide power to a respective further circuit that is isolated from the secondary-side power supply to the oscillator circuit.

[0034] That is, the same power supply circuit may be configured to supply electrical power to a plurality of floating circuits residing in various live voltages, such as in a 3- phase electricity meter. In such an arrangement, one isolation capacitor may be used for each phase and a common oscillator and driver / power stage may be provided for the power supply.

[0035] According to a second aspect of the disclosure, there is provided an electricity meter comprising the power supply circuit of the first aspect.

[0036] The electricity meter may be a multi-phase electricity meter. One rectifier circuit of the plurality of rectifier circuits, and the respective isolation capacitor, may be associated with each phase.

[0037] The above summary is intended to be merely exemplary and non-limiting. The disclosure includes one or more corresponding aspects, embodiments or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. It should be understood that features defined above in accordance with any aspect of the present disclosure or below relating to any specific embodiment of the disclosure may be utilized, either alone or in combination with any other defined feature, in any other aspect or embodiment or to form a further aspect or embodiment of the disclosure.

[0038] BRIEF DESCRIPTION OF DRAWINGS

[0039] These and other aspects of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, wherein:

[0040] Figure 1 depicts an example of phase voltage filtering circuitry for supplying an electricity meter;

[0041] Figure 2 depicts a example prior art circuit for supplying floating circuitry in an electricity meter;

[0042] Figure 3 depicts a power supply circuit for use in an electricity meter, according to an embodiment of the disclosure;

[0043] Figure 4 depicts the power supply circuit of Figure 3, with a return current path indicated;

[0044] Figure 5 depicts a power supply circuit for use in an electricity meter, according to a further embodiment of the disclosure;

[0045] Figure 6 depicts a power supply circuit for use in an electricity meter, according to a further embodiment of the disclosure; and

[0046] Figure ? depicts an electricity meter, according to a further embodiment of the disclosure.

[0047] DETAILED DESCRIPTION OF DRAWINGS

[0048] In known power supply circuits for electricity meters, floating circuits are typically powered from line voltages with capacitive droppers to a low (few volts) voltage and work only at every half line cycle. Such a power supply has a relatively low efficiency and may require implementation of a relatively large X-class capacitor to provide sufficient current to the floating circuit. Additionally the capacitor need to be dimensioned such that operation is guaranteed at the lowest possible line voltage and losses are then increased when operating at nominal operating voltage. This relatively large capacitor also means that apparent power consumption of the meter is relatively large. Another means of powering the floating circuit may be to implement a similar capacitive dropper, but to higher voltage. This higher voltage may then be converted down to low voltage with a buck converter. This may provide a small efficiency improvement over the above-described capacitive dropper directly to low voltage, though at additional cost.

[0049] A circuit 100 depicted in Figure 1 comprises typical input protection components of an electricity meter power supply. In the depicted example, the phase voltage is brought to the meter through a current limiting resistor 1 15. Any surge or impulse voltage or similar disturbance is clamped with a varistor 120 and protection capacitor 125, which may be an X-class capacitor.

[0050] An output 130 of the circuit 100 (denoted “To power supply”) may be rectified and / or regulated to provide a supply to a secondary side of the electricity meter, and thus also to any floating circuit.

[0051] In such known prior art circuits, the protection capacitor 125 may typically have a capacity of 47 nF, which may result in approximately 0.781 VA apparent power consumption at 230 VAC and at 50 Hz.

[0052] Figure 2 depicts an example prior art circuit 200 for supplying floating circuitry in an electricity meter. The circuit 200 is a capacitive dropper type power supply for powering the floating part connected to live phase voltage.

[0053] An input 205 is denoted ‘Live’. In an example, the input 205 may be coupled to a line side of the electricity meter. For example, the input 205 may correspond to one phase of a multi-phase meter, and therefore may be at a phase voltage, e.g. 110 V or 240 V, or the like. The input 205 may be coupled, directly or indirectly, to a live terminal of the electricity meter.

[0054] Also depicted is a neutral line 210, which may also be coupled, directly or indirectly, to a neutral terminal of the electricity meter.

[0055] A current-limiting resistor 215, a varistor 220 and a protection capacitor 225, e.g. an X-class capacitor, are typical protection components for a power supply, as described above with reference to the circuit 100 of Figure 1 .

[0056] An output 230 of the circuit 200 (denoted “To power supply”) may be rectified and / or regulated to provide a secondary-side power supply.

[0057] In this example, a Zener diode 240 is used to create voltage difference in the floating part which is then supplied to rectifier and regulator 250, which typically consists of rectifier diode, filtering capacitor and a Zener clamp diode. The live phase voltage, e.g. voltage at the input 205, provides a ground reference point 265 for the rectifier and regulator 250, and also for the actual floating circuit to be powered.

[0058] In this non-limiting example, the actual circuit to be powered is an analog-to- digital converter 260 (ADC). The ADC 260 is isolated from rest of the circuit with an isolation barrier 270, which may comprise any of: a capacitor; a digital isolator integrated circuit (IC); and / or an optocoupler.

[0059] For the example circuit 200 of Figure 2, wherein the live phase voltage at the input 205 is 230V at 50Hz, and in order to provide enough current for the floating side power supply, the protection capacitor 225 may be an X-class capacitor with a capacity of 150 nF to 220 nF. In such an example, the circuit 200 described herein would therefore exhibit approximately 2.49 VA apparent power consumption.

[0060] Turning now to Figure 3, there is depicted a power supply circuit 300 for use in an electricity meter, according to an embodiment of the disclosure. That is, the circuit 300 is for powering a floating live-side circuit 390 (hereafter ‘floating circuit’ or ‘floating part’ 390) of the meter.

[0061] An input 305 is denoted ‘Live’. In an example, the input 305 may be coupled to a line side of the electricity meter. For example, the input 305 may correspond to one phase of a multi-phase meter, and therefore may be at a phase voltage, e.g. 110 V or 240 V, or the like. The input 305 may be coupled, directly or indirectly, to a terminal of the electricity meter.

[0062] Also depicted is a neutral line 310, which may also be coupled, directly or indirectly, to a terminal of the electricity meter.

[0063] A current-limiting resistor 315, a varistor 320 and a protection capacitor 325, e.g. an X-class capacitor, are typical protection components for a power supply, as described above with reference to the circuit 100 of Figure 1 .

[0064] An output 330 of the circuit 300 (denoted “To power supply”) may be rectified and / or regulated to provide a secondary-side power supply.

[0065] In this non-limiting example, the actual floating circuit 390 to be powered comprises a rectifier and regulator 350 (which may comprise a rectifier diode, filtering capacitor and a Zener clamp diode), and an analog-to-digital converter 360 (ADC). The ADC 360 is isolated from rest of the circuit with an isolation barrier 370, which may comprise any of: a capacitor; a digital isolator integrated circuit (IC); and / or an optocoupler. Also depicted is an isolation capacitor 375 and an oscillator circuit 380. In this example, the oscillator circuit 380 comprises an oscillator (which may be as simple as an RC oscillator). The example oscillator circuit 380 also comprises a driver (also known generally as a power stage). In non-limiting example embodiments, the driver may comprise a half bridge, totem pole transistors, an operational amplifier, a comparator, a motor driver IC, or a H-bridge.

[0066] The oscillator circuit 380 and isolation capacitor 375 are configured to provide a capacitive power supply for the live side circuit, e.g. to the rectifier and regulator 350 and to the ADC 360.

[0067] In the depicted example, the oscillator circuit 280 has a ground reference 385 which is coupled to the neutral line 310.

[0068] For purposes of example, the output 330 is provided to a secondary-side power supply 335, which may for example comprise a floating output flyback power supply or other switch-mode power supply, is depicted. The secondary-side power supply 335 may provide a supply of power to the oscillator circuit 380.

[0069] That is, in the depicted circuit 300, the rectifier circuit 350 is configured to rectify an oscillating signal received from the oscillator circuit 380, via the isolation capacitor 375, and to provide power to a further circuit, e.g. the ADC 360, that is isolated from a secondary-side power supply 335 to the oscillator circuit 380.

[0070] Figure 4 depicts the power supply circuit 300 of Figure 3, with a current path indicated. The protection capacitor 325 provides return current path for supply current coming through isolation capacitor 375.

[0071] In Figure 4, it can be seen that the current path from the oscillator circuit 380 is through the isolation capacitor 375 and back through the protection capacitor and the ground reference 385.

[0072] Isolation capacitor 375 can be relatively small to provide enough operating current for the floating part 390, e.g. for the rectifier and regulator 350 and the ADC 360.

[0073] The oscillator circuit 380 may be configured to operate at a relatively high frequency compared to a frequency of the phase voltage. For example, the line phase voltage, e.g. at input 305, may have a frequency of 50 Hz, whereas the oscillator circuit 380 may be configured to generate a signal having a frequency of 100 to 1000 kHz.

[0074] Advantageously, such a frequency mismatch between the 50 Hz live side of the floating circuit 390 (including its harmonics) and the high frequency of the oscillator circuit 380 may improve an efficiency of the powering of the floating circuit 390. For example, a 2.2 nF isolation capacitor driven from the oscillator circuit 380 with 12 V DC-voltage (6 V midpoint at power stage) and at 250 kHz may provide about 20 milliamps of current to the live circuit side. In the depicted circuit 300 about half of this is unusable, as the live voltage is higher for a half cycle (10 milliseconds) at 50 Hz compared to the neutral referenced oscillator circuit 380. However, this same 2.2 nF capacitor provides about 1 .45 mega-ohm capacitive reactance towards the oscillator circuit. As such, a negligible current flows from the live side to the power supply side.

[0075] Figure 5 depicts a further a power supply circuit 400 for use in an electricity meter, according to an embodiment of the disclosure.

[0076] For purposes of brevity, references to similar components to those of the circuit of Figures 3 and 4 are simply incremented by 100, and are not described in more detail. That is, the circuit 400 also comprises: an input 405 denoted ‘Live’; a neutral line 410; a current-limiting resistor 415, a varistor 420; a protection capacitor 425; an output 430; a rectifier and regulator 450; an ADC 460; an isolation barrier 470; an isolation capacitor 475; a floating circuit 490; and an oscillator circuit 480.

[0077] The circuit 400 of Figure 5 shows different arrangement for return current path, wherein neutral is not available at the power supply side of the oscillator circuit 380. In this alternative example, a further capacitor 495, which may be similar to the isolation capacitor 475 is added to provide a return current path. This allows the power supply to be floating in reference to other (not depicted) parts of the electricity meter.

[0078] Figure 6 depicts a power supply circuit 500 for use in an electricity meter, according to a further embodiment of the disclosure. For purposes of brevity, references to similar components to those of the circuit of Figures 3 and 4 are simply incremented by 100, and are not described in more detail. That is, the circuit 500 also comprises: an input 505 denoted ‘Live’; a neutral line 510; a current-limiting resistor 515, a varistor 520; a protection capacitor 525; an output 530; a rectifier and regulator 550; an ADC 560; an isolation barrier 570; an oscillator circuit 580; ground reference 585; and floating circuit 590a.

[0079] The power supply circuit 500 is essentially the same as the power supply circuit 300 of Figures 3 and 4, except modified to show how the same circuit can power multiple floating circuits residing in various live voltages, such as in a 3-phase electricity meter. For purposes of simplicity of illustration, only a first floating circuit 590a is depicted.

[0080] In the example, one isolation capacitor 575a, 575b, 575c is used for each phase, and the common oscillator circuit 380 is used as the power supply. The circuit 500 shows a neutral referenced arrangement, e.g. the ground reference 585, but it will be appreciated that a floating arrangement described in Figure 5 is also applicable, e.g. with an implementation of the further capacitor 495.

[0081] Figure 7 depicts an electricity meter 600, according to a further embodiment of the disclosure.

[0082] For purposes of example, the electricity meter 600 is a multi-phase electricity meter. In the example, the electricity meter 600 is a 3-phase meter, e.g. a first phase denoted L1 , and second phase denoted L2, and third phase denote L3 and a neutral line denoted N. A line side 605 of the electricity meter 600 may be coupled to a supply, such as the electrical grid. A load side 610 of the electricity meter 600 may be coupled to one or more loads. Although only two ports are depicted on the electricity meter 600, it will be understood that this is for purposes of illustration only and further ports may be implemented. For example, in some embodiments the meter may comprise one of more Distributed Energy Resource (DER) ports. As such, the electricity meter 600 may be a multi-port meter in some embodiments.

[0083] The electricity meter 600 comprises the power supply circuit 500 as described above with reference to Figure 6. In other embodiments, the power supply circuit 500 may comprise the power supply circuit 300, 400 as described above with reference to Figures 3 to 5.

[0084] The power supply circuit 500 comprises a plurality of floating circuits 590a, 590b, 590c. Each floating circuit 590a, 590b, 590c comprises an ADC (not depicted) coupled to a sensor C1 , C2, C3 for metering current and / or voltage characteristics of a respective phase L1 , L2, L3 of the electrical power supply. For purposes of illustration only, three sensors C1 , C2, C3 are depicted, although it will be appreciated that other configurations having fewer than or greater than three sensors may be implemented. That is, the power supply circuit 500 comprises a rectifier circuit and associated ADC for each phase L1 , L2, L3.

[0085] Although the disclosure has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure, which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in any embodiments, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein. REFERENCE NUMERALS

[0086] 100 prior art circuit 40 420 varistor

[0087] 115 current limiting resistor 425 protection capacitor

[0088] 120 varistor 430 output

[0089] 125 protection capacitor 435 secondary-side power supply

[0090] 130 output 450 rectifier and regulator

[0091] 200 prior art circuit 45 460 ADC

[0092] 205 input 470 isolation barrier

[0093] 210 neutral line 475 isolation capacitor

[0094] 215 current limiting resistor 480 oscillator circuit

[0095] 220 varistor 490 floating live-side circuit

[0096] 225 protection capacitor 50 495 further capacitor

[0097] 230 output 500 power supply circuit

[0098] 240 Zener diode 505 input

[0099] 250 rectifier and regulator 510 neutral line

[0100] 260 ADC 515 current limiting resistor

[0101] 265 ground reference point 55 520 varistor

[0102] 270 isolation barrier 525 protection capacitor

[0103] 280 oscillator circuit 530 output

[0104] 300 power supply circuit 535 secondary-side power supply

[0105] 305 input 550 rectifier and regulator

[0106] 310 neutral line 60 560 ADC

[0107] 315 current limiting resistor 570 isolation barrier

[0108] 320 varistor 575a isolation capacitor

[0109] 325 protection capacitor 575b isolation capacitor

[0110] 330 output 575c isolation capacitor

[0111] 335 secondary-side power supply 65 580 oscillator circuit

[0112] 350 rectifier and regulator 585 ground reference

[0113] 360 ADC 590a floating live-side circuit

[0114] 370 isolation barrier 590b floating live-side circuit

[0115] 375 isolation capacitor 590c floating live-side circuit

[0116] 380 oscillator circuit 70 600 electricity meter

[0117] 385 ground reference 605 line side

[0118] 390 floating live-side circuit 610 load side

[0119] 400 power supply circuit C1 Current transformer

[0120] 405 input C2 Current transformer

[0121] 410 neutral line 75 C3 Current transformer

[0122] 415 current limiting resistor

Claims

CLAIMS1 . A power supply circuit for use in an electricity meter, comprising: a rectifier circuit; an oscillator circuit; and an isolation capacitor, wherein the rectifier circuit is configured to rectify an oscillating signal received from the oscillator circuit, via the isolation capacitor, and to provide power to a further circuit that is isolated from a secondary-side power supply to the oscillator circuit.

2. The power supply circuit of claim 1 , wherein the secondary-side power supply to the oscillator circuit is configured to be electrically isolated from a line and / or load side of the electricity meter.

3. The power supply circuit of any preceding claim, comprising the further circuit, wherein the further circuit comprises at least one analog-to-digital converter, ADC, configured to sense a current and / or voltage corresponding to a / the line and / or load side of the electricity meter.

4. The power supply circuit of claim 3, wherein the further circuit is isolated from the secondary-side power supply to the oscillator circuit by an isolation barrier comprising at least one of: one or more capacitors; a digital isolator integrated circuit; an optocoupler.

5. The power supply circuit of any preceding claim, wherein the rectifier circuit comprises: a rectifier for rectifying the oscillating signal received from the oscillator circuit; and at least one voltage regulator configured to receive a rectified voltage from the rectifier and to provide a regulated voltage to the further circuit.

6. The power supply circuit of any preceding claim, wherein a capacity of the isolation capacitor is selected to: present a relatively high impedance to frequency components of 60 Hz or less on the oscillating signal from the oscillator circuit; and present a relatively low impedance to frequency components of 1 kHz or greater on the oscillating signal from the oscillator circuit, such that a supply of current is provided from the oscillator circuit to the rectifier circuit.

7. The power supply circuit of any preceding claim, wherein the oscillator circuit is configured to generate the oscillating signal having a frequency of at least 100kHz.

8. The power supply circuit of any preceding claim, wherein the oscillator circuit comprises a driver, and optionally wherein the driver comprises: a half bridge; or a totem pole transistor; or a operational amplifier; or a comparator; or a motor driver IC; or a H-bridge.

9. The power supply circuit of any preceding claim, wherein the secondary-side power supply to the oscillator circuit comprises a floating output flyback power supply.

10. The power supply circuit of any preceding claim, wherein the secondary-side power supply to the oscillator circuit is protected by a line-filtering capacitor and at least one of: a voltage limiting resistor; and a varistor.1 1 . The power supply circuit of claim 10, wherein the line-filtering capacitor is configured to be connected between a / the line side and a neutral of the electricity meter, and wherein the line side is at a substantially same potential as the rectifier circuit.

12. The power supply circuit of any preceding claim, wherein the power supply to the oscillator circuit is referenced to one of: neutral; a rectified negative line voltage; or a rectified positive line voltage.

13. The power supply circuit of any preceding claim, comprising a plurality of rectifier circuits, each rectifier circuit configured to rectify an oscillating signal received from the oscillator circuit via a respective isolation capacitor, and to provide power to a respective further circuit that is isolated from the secondary-side power supply to the oscillator circuit.

14. An electricity meter comprising the power supply circuit of any preceding claim.

15. The electricity meter of claim 14, when dependent upon claim 13, wherein: the electricity meter is a multi-phase electricity meter; and one rectifier circuit of the plurality of rectifier circuits, and the respective isolation capacitor, is associated with each phase.

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