GB2474476A - An isolating capacitor using a PCB layer as a dielectric - Google Patents

An isolating capacitor using a PCB layer as a dielectric Download PDF

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Publication number
GB2474476A
GB2474476A GB0918036A GB0918036A GB2474476A GB 2474476 A GB2474476 A GB 2474476A GB 0918036 A GB0918036 A GB 0918036A GB 0918036 A GB0918036 A GB 0918036A GB 2474476 A GB2474476 A GB 2474476A
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GB
United Kingdom
Prior art keywords
circuit
isolator
electrical
capacitor
electrical isolator
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB0918036A
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GB0918036D0 (en
Inventor
William Michael James Holland
Jonathan Ephraim David Hurwitz
Iain Barnett
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Broadcom Networks Edinburgh Ltd
Original Assignee
Gigle Semiconductor Ltd
Gigle Networks Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Gigle Semiconductor Ltd, Gigle Networks Ltd filed Critical Gigle Semiconductor Ltd
Priority to GB0918036A priority Critical patent/GB2474476A/en
Publication of GB0918036D0 publication Critical patent/GB0918036D0/en
Publication of GB2474476A publication Critical patent/GB2474476A/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/0213—Electrical arrangements not otherwise provided for
    • H05K1/0254—High voltage adaptations; Electrical insulation details; Overvoltage or electrostatic discharge protection ; Arrangements for regulating voltages or for using plural voltages
    • H05K1/0256—Electrical insulation details, e.g. around high voltage areas
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
    • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
    • H03K17/687—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors
    • H03K17/689—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors with galvanic isolation between the control circuit and the output circuit
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
    • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
    • H03K17/687—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors
    • H03K17/689—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors with galvanic isolation between the control circuit and the output circuit
    • H03K17/691—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors with galvanic isolation between the control circuit and the output circuit using transformer coupling
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/0213—Electrical arrangements not otherwise provided for
    • H05K1/0237—High frequency adaptations
    • H05K1/0239—Signal transmission by AC coupling
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/16—Printed circuits incorporating printed electric components, e.g. printed resistor, capacitor, inductor
    • H05K1/162—Printed circuits incorporating printed electric components, e.g. printed resistor, capacitor, inductor incorporating printed capacitors
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/09—Shape and layout
    • H05K2201/09209—Shape and layout details of conductors
    • H05K2201/0929—Conductive planes
    • H05K2201/09309—Core having two or more power planes; Capacitive laminate of two power planes
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/09—Shape and layout
    • H05K2201/09818—Shape or layout details not covered by a single group of H05K2201/09009 - H05K2201/09809
    • H05K2201/09972—Partitioned, e.g. portions of a PCB dedicated to different functions; Boundary lines therefore; Portions of a PCB being processed separately or differently

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Dc-Dc Converters (AREA)

Abstract

Digital feedback signals are coupled to the high-voltage primary circuit 42 of a switched mode power supply (SMPS) through one or more capacitors 56 which comprise metal layers on opposing sides of a printed circuit board (PCB) or on opposing sides of an internal layer of the PCB (figure 3). This form of capacitive feedback is cheaper than a conventional capacitor or a feedback transformer and consumes less power than an opto-isolator. Two PCB capacitors may be used to couple a data-modulated clock to the controller 58. PCB capacitors may be used in an intelligent plug to couple signals to a controller switching AC input mains to an AC mains feed or to an auxiliary circuit (108,112, figure 4). The technique may be used in a multimedia home networking node.

Description

Electrical isolators
Field of the invention
The present invention relates to a low power electrical isolator circuit operable to provide isolation of a low voltage circuit from a high voltage circuit whilst providing for coupling of a signal from the low voltage circuit to the high voltage circuit.
Background to the invention
Mains voltage powered consumer products, such as multimedia home networking nodes, are required for reasons of safety to have electrical isolation between mains voltage circuitry and low voltage circuitry. Despite the electrical isolation there is often a need to convey signals across the electrical isolation barrier between the low voltage circuitry and the mains voltage circuitry.
The coupling of control signals from a switch mode power supply (SMPS) present on a low voltage side to mains voltage circuitry on a high voltage side is an example of such a need.
A known SMPS circuit is shown in Figure 1. The SMPS circuit 10 comprises circuitry on a mains, i.e. high, voltage side 12 and circuitry on a low voltage side 14, which are DC isolated from each other. More specifically, the SMPS circuit comprises a full wave rectifier with smoothing 16, which receives an AC mains signal and generates a substantially smooth high voltage DC voltage. The SMPS circuit 10 also comprises a transformer having a primary winding 18 and a secondary winding 20. A load circuit 22, e.g. multimedia home networking node circuitry, is electrically connected to the secondary winding. Feedback from the secondary winding 20 to the primary winding 18 is provided by means of a control feedback circuit 24, which is electrically connected to the secondary winding 20 and which drives an opto-isolator 26, which in turn drives a controller circuit 28. An output from the controller circuit drives a FET 30 in series with the primary winding 18 of the transformer.
The control feedback circuit 24 is operative to convert the voltage signal across the secondary winding 20 to a digital signal, which is coupled across the isolation barrier by the opto-isolator 26 to the controller 28. The controller 28 is operative to convert the digital signal into a Pulse Width Modulated signal that is operative to switch the EEl 30 on and off to modulate the current flowing in the primary winding 18. The primary and secondary windings 18, 20 provide for DC isolation between the high and low voltage sides 12, 14 whilst providing for coupling of power from the high voltage side 12 to the low voltage side 14. The opto-isolator 26 provides for DC iso'ation between the high and low voltage sides 12, 14 whilst providing for coupling of feedback control signals from the low voltage side 14 to the high voltage side 12.
According to another known approach, a transformer is used instead of the opto-isolator of Figure 1.
A disadvantage of using an opto-isolator in the circuit of Figure 1 is its comparatively high power dissipation. A disadvantage of using a transformer in the circuit of Figure 1 is its typically large size and its comparatively high cost.
The present invention has been devised in the light of the above mentioned problems with the known electrical isolator circuit.
It is therefore an object for the present invention to provide an electrical isolator circuit that is operable to isolate a low voltage circuit from a high voltage circuit whilst providing for coupling of signals from the low voltage circuit to the high voltage circuit.
It is a further object for the present invention to provide a low power electrical isolator circuit that is operable to isolate a low voltage circuit from a high voltage circuit whilst providing for coupling of signals from the low voltage circuit to the high voltage circuit.
Statement of invention
According to a first aspect of the present invention there is provided an electrical isolator circuit comprising: a high voltage circuit; a (ow voltage circuit, the high voltage circuit and low voltage circuit being DC isolated from each other; and a DC isolator comprising a capacitor, the electrical isolator circuit being configured such that the DC isolator is operable to couple a signal from the low voltage circuit to the high voltage circuit, the first and second plates of the capacitor being defined by conductive layers of a printed circuit board and the dielectric of the capacitor being defined by a non-conducting part of the printed circuit board.
In use, the DC isolator couples a signal from the low voltage circuit to the high voltage circuit, e.g. for control of the high voltage circuit by means of the signal. The electrical isolator circuit may be configured such that the first and second plates of the capacitor are respectively on a (ow voltage side and a high voltage side of the electrical isolator circuit. Capacitors in the form of discrete components that are suitable for the coupling of a signal from the low voltage circuit to the high voltage circuit tend to be expensive. Hence, the printed circuit board defined (i.e. non discrete) capacitor of the present invention can provide a lower cost alternative to a discrete capacitor. Electrical circuits of at least one of the high voltage circuit and the low voltage circuit may be mounted on and interconnected by means of the printed circuit board that defines the capacitor.
The formation of the capacitor of the present invention in a printed circuit board may offer a cost advantage over and lower power consumption than the known electrical isolator of Figure 1.
Alternatively or in addition, the capacitor may be connected in series between the low voltage circuit and the high voltage circuit.
Alternatively or in addition, the capacitor may have a capacitance of less than 100 pF. More specifically, the capacitor may have a capacitance of less than 50 pF. More specifically, capacitor may have a capacitance of less than 10 pF, such as substantially 5 pF. As regards power dissipation, substantially no power is dissipated in the capacitor.
Alternatively or in addition, at least one plate of the capacitor is defined by a layer of metal in or on the printed circuit board. The layer of metal may be formed on a surface, such as an upper or lower surface of the printed circuit board. Hence, the first and second plates of the capacitor may be formed on opposing upper and lower surfaces of the printed circuit board such that the non-conducting body of the printed circuit board constitutes the dielectric of the capacitor. Alternatively, at least one layer of metal may be embedded within the printed circuit board. Hence, at least one of the first and second plates of a capacitor may be formed within the printed circuit board such that they are spaced apart from each other and with their footprints overlapping, whereby a non-conducting part of the printed circuit board between the first and second plates constitutes the dielectric of the capacitor. The first and second plates may share substantially the same footprint.
Alternatively or in addition, a high voltage AC signal in the context of the present invention may be an AC voltage of 50 Vrms or greater according to standards defined by the International Electrotechnical Commission, such as an AC voltage of substantially 110 Vrms or substantially 230 Vrms. Thus, the high voltage AC signal may be a domestic mains voltage signal or a mains voltage signal in a ship.
Alternatively or in addition, a low voltage signal in the context of the present invention may be an AC voltage of less than 50 Vrms or a DC voltage of less than 120 V according to standards defined by the International Electrotechnical Commission. More specifically, the low voltage signal may be a DC voltage of less than substantiafly 15 volts, such as a voltage of 12 volts. More specifically, the low voltage signal may be a DC voltage of substantially 5 volts or less.
Alternatively or in addition, the electrical isolator circuit may further comprise a power DC isolator that is operable to couple electrical power from the high voltage circuit to the low voltage circuit.
More specifically, the power DC isolator may comprise a transformer with the high voltage AC circuit comprising a primary winding of the transformer and the low voltage circuit comprising a secondary winding of the transformer. More specifically, the secondary winding of the transformer may provide electrical power to the low voltage circuit. Alternatively or in addition, the primary winding of the transformer may be electrically connected to a source of AC power.
Alternatively or in addition, the high voltage AC circuit may comprise a switch, such as a FET switch.
More specifically, the high voltage circuit may be configured such that the switch is actuated in dependence on a signal coupled by the capacitor of the DC isolator.
More specifically and where the switch is a FET switch, the high voltage circuit may be configured such that a gate of the FET switch is electrically connected (either directly or indirectly) to the capacitor such that the FET is controlled by the capacitor coupled signal. Where the high voltage AC circuit comprises a primary winding of a transformer, the FET switch may be in series with the primary winding. In use, the FET switch may be used to turn the primary winding on and off in dependence on an output from the low voltage circuit.
According to a first embodiment, the electrical isolator circuit may further comprise a switch mode power supply (SMPS), a primary winding of the switch mode power supply forming part of the high voltage circuit, a secondary winding of the switch mode power supply forming part of the low voltage circuit and a feedback circuit of the switch mode power supply from the high voltage circuit to the low voltage circuit comprising the DC isolator. Thus, the switch mode power supply may comprise a control feedback circuit, which is electrically connected to the secondary winding and which drives the capacitor, which in turn drives a controller circuit. An output from the controller circuit drives a FET in series with the primary winding.
According to a second embodiment, the electrical isolator circuit may further comprise a switch, e.g. a FET switch, which is operative to turn on and off an auxiliary power supply line in dependence upon the signal coupled by the capacitor of the DC isolator. The auxiliary power supply line may be a power supply line other than the power supply to a primary winding of a transformer of the electrical isolator circuit.
More specifically, the auxiliary power supply line may be in parallel with the power supply to a primary winding of a transformer of the electrical isolator circuit.
Alternative'y or in addition, the auxiliary power supply line may provide electrical power to an actuated circuit of the high voltage circuit. For example, the actuated circuit may be an operative circuit, such as an auxiliary power regulation circuit, on the high voltage side, with actuation of the operative circuit having no adverse impact on coupling of power from the high voltage circuit to the low voltage circuit and no adverse impact on the coupling of a signal from the low voltage circuit to the high voltage circuit by means of the DC isolator.
Alternatively or in addition, the electrical isolator circuit may comprise a controller circuit that is operable to drive the switch and which is operable in dependence on the signal coupled by the capacitor of the DC isolator.
The controller circuit may be operable to shape the signal received from the capacitor to a form appropriate for driving the switch. For example and where the switch is a FET switch, the controller circuit may comprise a latch so as to provide a regular digital signal to drive the gate of the FET switch.
Alternatively or in addition, the DC isolator may comprise a plurality of capacitors in parallel with each other, whereby each of a plurality of signals may be coupled by a respective capacitor from the low voltage circuit to the high voltage circuit. Hence, the plurality of capacitors may be used to provide for data communication from the low voltage circuit to the high voltage circuit. For example, data communication may involve communication of a data modulated system clock.
According to a second aspect of the present invention, there is provided an electrical apparatus, such as might form part of a multimedia home networking node, comprising the electrical isolator circuit according to the first aspect of the present invention.
More specifically, the electrical apparatus may further comprise a load circuit. Power to the load circuit may be provided by a power DC isolator of the electrical isolator circuit. An output from the load circuit may be electrically coupled to the DC isolator such that the load circuit provides a signal to the capacitor of the DC isolator.
Further embodiments of the second aspect of the present invention may comprise one or more features of the first aspect of the present invention.
According to a further aspect of the present invention, there is provided and electrical isolator circuit comprising a first circuit; a second circuit, the first circuit and the second circuit being DC isolated from each other; and a DC isolator comprising a capacitor, the electrical isolator circuit being configured such that the DC isolator is operable to couple a signal from the second circuit to the first circuit, the first and second plates of the capacitor being defined by conductive layers of a printed circuit board and the dielectric of the capacitor being defined by a non-conducting part of the printed circuit board.
Mores specifically, the first circuit may be a high voltage AC circuit.
Alternatively or in addition, the second circuit may be a low voltage circuit.
Further embodiments of the further aspect of the present invention may comprise one or more features of the first aspect of the present invention.
Brief description of drawings
Further features and advantages of the present invention will become apparent from the following specific description, which is given by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram of a known electrical isolator circuit; Figure 2 is a circuit diagram of an SMPS circuit having an electrical isolator circuit according to a first embodiment of the present invention; Figure 3 provides plan and cross-section views of a printed circuit board configured to form part of the DC isolator of the present invention; and Figure 4 is a circuit diagram of electrical apparatus having an electrical isolator circuit according to a second embodiment of the present invention.
The Switch Mode Power Supply (SMPS) circuit 40 of Figure 2 is similar to the circuit of Figure 1 with the exception of the feedback path from the low voltage side to the high voltage side as will become apparent from the following description. The SMPS circuit 40 comprises circuitry on a mains, i.e. high, voltage side 42 and circuitry on a low voltage side 44, which are DC isolated from each other. More specifically, the SMPS circuit 40 comprises a full wave rectifier with smoothing 46, which receives an AC mains signal and generates a substantially smooth high voltage DC voltage. The AC mains signal is an AC voltage of substantially 110 Vrms or substantially 230 Vrms. Circuitry on the low voltage side operates at a DC voltage of substantially 5 volts.
The SMPS circuit 40 also comprises a transformer having a primary winding 48 and a secondary winding 50. A load circuit 52, e.g. multimedia home networking node circuitry, is electrically connected to the secondary winding. Feedback from the secondary winding 50 to the primary winding 48 is provided by means of a control feedback circuit 54, which is electrically connected to the secondary winding 50 and which drives a capacitor, which in turn drives a controller circuit 58. An output from the controller circuit 58 drives a FET 60 in series with the primary winding 48 of the transformer. The control feedback circuit 54 is operative to convert the voltage signal across the secondary winding 50 to a digital signal, which is coupled by the capacitor 56 across the isolation barrier to the controller 58. The controller 58 is operative to convert the digital signal into a Pulse Width Modulated signal that is operative to switch the FET 60 on and off to modulate the current flowing in the primary winding 48. The primary and secondary windings 48, 50 provide for DC isolation between the high and low voltage sides 42, 44 whilst providing for coupling of power from the high voltage side 42 to the low voltage side 44. The capacitor 56 provides for DC isolation between the high and low voltage sides 42, 44 whilst providing for coupling of feedback control signals from the low voltage side 44 to the high voltage side 42. As is described below with reference to Figure 3, the capacitor 56 is formed in the printed circuit board on which the SMPS circuit 40 is mounted.
Plan 70 and cross-section 72 views of the capacitor of Figure 2 are shown in Figure 3. As can be seen, each of the first 74 and second 76 plates of the capacitor are defined by respective metal layers on the top and bottom surfaces of the printed circuit board. The metal layers are disposed such that they share the same footprint and so that the non-conductive substrate 78 of the printed circuit board defines the dielectric of the capacitor. The formation of metal tracks and of larger area structures, such the metal layers of the first and second plates, on a printed circuit board substrate is a process that is well known to the skilled person.
Alternatively, one or more capacitor plates are defined by metal layers embedded within the substrate. The provision of embedded metal tracks and of larger area structures, such the metal layers of the first and second plates, is a process that is well known to the skilled person. Typically, the capacitor has a value of substantially 5 pF, which is appropriate where the controller 58 has an input capacitance of substantially 2 pF.
According to an un-illustrated form of the SMPS circuit 40 of Figure 2, two capacitors are employed instead of the single capacitor 56 of Figure 2.
The two capacitors respectively provide for coupling of a data modulated system clock that is operative to provide for communications from the low voltage side to the high voltage side. The control feedback circuit 54 of Figure 2 is configured to generate messages in the form of data that modulates a system clock, the modulated system clock being conveyed by means of the capacitors to the controller 58. The controller 58 is configured to demodulate the modulated system clock to recover the data with the controller being operative to change the PWM signal in dependence on the recovered data.
Electrical apparatus 90 having an electrical isolator circuit according to a second embodiment of the present invention is shown in Figure 4. The electrical apparatus 90 comprises a transformer having a primary winding 92 that receives a mains AC signal 94 and a secondary winding 96 that is electrically coupled to a load circuit 98. Hence, the electrical apparatus 90 comprises circuitry on a mains, i.e. high, voltage side 91 and circuitry on a low voltage side 93, which are DC isolated from each other. An output line from the load circuit 98 is electrically connected to a capacitor 100, which is operative to provide for DC isolation between the high and low voltage sides 91, 93 whilst providing for coupling of feedback control signals over the output line from the low voltage side 93 to the high voltage side 91.
The capacitor 100 is formed in the printed circuit board on which the electrical apparatus 90 is mounted as is described above with reference to Figure 3. The capacitor is connected to a controller 102 on the high voltage side 91 with the controller driving a gate of a first FET switch 104 and a gate of a second FET switch 106. The controller 102 is operative to shape the signal coupled by the capacitor 100 such that it is capable of driving the gates of the first and second FETs. For example, the controller comprises a latch that receives attenuated control signals from the capacitor 100 and provides corresponding output signals having high and low voltage values that are capable of turning the FET switches on and off.
The first FET 104 of the circuit of Figure 4 is in series with a line of an auxiliary AC mains feed 108 tapped from the mains AC signal 94.
According to a form of the present embodiment, the electrical apparatus forms part of an intelligent plug with the auxiliary AC mains feed 108 constituting the supply to whatever electrical device is plugged into the intelligent plug. Hence, the first FET 104 can be used to switch on and off the electrical device plugged into the intelligent plug.
The second FET 106 of the circuit of Figure 4 is in series with a line of another auxiliary AC mains feed 110 to an auxiliary circuit 112. Hence, the second FET 106 can be used to switch on and off the auxiliary circuit, e.g. for power conservation purposes.

Claims (29)

  1. CLAIMS: 1. An electrical isolator circuit comprising: a high voltage circuit; a low voltage circuit, the high voltage circuit and low voltage circuit being DC isolated from each other; and a DC isolator comprising a capacitor, the electrical isolator circuit being configured such that the DC isolator is operable to couple a signal from the low voltage circuit to the high voltage circuit, the first and second plates of the capacitor being defined by conductive layers of a printed circuit board and the dielectric of the capacitor being defined by a non-conducting part of the printed circuit board.
  2. 2. The electrical isolator circuit according to claim 1 configured such that the first and second plates of the capacitor are respectively on a low voltage side and a high voltage side of the electrical isolator circuit.
  3. 3. The electrical isolator circuit according to claim 1 or 2, in which an electrical circuit of at least one of the high voltage circuit and the low voltage circuit is mounted on and interconnected by means of the printed circuit board that defines the capacitor.
  4. 4. The electrical isolator circuit according to any preceding claim, in which the capacitor is connected in series between the ow voltage circuit and the high voltage circuit.
  5. 5. The electrical isolator circuit according to any preceding claim, in which the capacitor has a capacitance of less than 100 pF.
  6. 6. The electrical isolator circuit according to any preceding claim, in which at least one plate of the capacitor is defined by a layer of metal in or on the printed circuit board.
  7. 7. The electrical isolator circuit according to claim 6, in which the layer of metal is formed on a surface of the printed circuit board.
  8. 8. The electrical isolator circuit according to claim 6 or 7, in which the first and second plates of the capacitor are formed on opposing upper and lower surfaces of the printed circuit board such that the non-conducting body of the printed circuit board constitutes the dielectric of the capacitor.
  9. 9. The electrical isolator circuit according to claim 6, in which at least one layer of metal is embedded within the printed circuit board.
  10. 10. The electrical isolator circuit according to claim 9, in which at least one of the first and second plates of a capacitor are formed within the printed circuit board such that they are spaced apart from each other and with their footprints overlapping, whereby a non-conducting part of the printed circuit board between the first and second plates constitutes the dielectric of the capacitor.
  11. 11. The electrical isolator circuit according to any preceding claim, in which a high voltage AC signal in the context of the present invention is an AC voltage of 50 Vrms or greater according to standards defined by the international Electrotechnical Commission.
  12. 12. The electrical isolator circuit according to any preceding claim, in which a low voltage signal in the context of the present invention is an AC voltage of less than 50 Vrms or a DC voltage of less than 120 V according to standards defined by the International Electrotechnical Commission.
  13. 13. The electrical isolator circuit according to claim 12, in which the low voltage signal is a DC voltage of less than substantially 15 volts.
  14. 14. The electrical isolator circuit according to any preceding claim further comprising a power DC isolator that is operable to couple electrical power from the high voltage circuit to the low voltage circuit.
  15. 15. The electrical isolator circuit according to claim 14, in which the power DC isolator comprises a transformer with the high voltage AC circuit comprising a primary winding of the transformer and the low voltage circuit comprising a secondary winding of the transformer, with the secondary winding of the transformer providing electrical power to the low voltage circuit.
  16. 16. The electrical isolator circuit according to any preceding claim, in which the high voltage AC circuit comprises a switch.
  17. 17. The electrical isolator circuit according to claim 16, in which the high voltage circuit is configured such that the switch is actuated in dependence on a signal coupled by the capacitor of the DC isolator.
  18. 18. The electrical isolator circuit according to claim 17, in which the switch is a FET switch, the high voltage circuit being configured such that a gate of the FET switch is electrically connected to the capacitor such that the FET switch is controlled by the capacitor coupled signal.
  19. 19. The electrical isolator circuit according to claim 18, in which the high voltage AC circuit comprises a primary winding of a transformer and the FET switch is in series with the primary winding.
  20. 20. The electrical isolator circuit according to any preceding claim, in which the electrical isolator circuit further comprises a switch mode power supply (SMPS), a primary winding of the switch mode power supply forming part of the high voltage circuit, a secondary winding of the switch mode power supply forming part of the low voltage circuit and a feedback circuit of the switch mode power supply from the high voltage circuit to the low voltage circuit comprising the DC isolator.
  21. 21. The electrical isolator circuit according to claim 20, in which the switch mode power supply comprises a control feedback circuit, which is electrically connected to the secondary winding and which drives the capacitor, which in turn drives a controller circuit, with an output from the controller circuit driving a switch in series with the primary winding.
  22. 22. The electrical isolator circuit according to any one of claims I to 19, in which the electrical isolator circuit further comprises a switch which is operative to turn on and off an auxiliary power supply line in dependence upon the signal coupled by the capacitor of the DC isolator.
  23. 23. The electrical isolator circuit according to claim 22, in which the auxiliary power supply line is in parallel with the power supply to a primary winding of a transformer of the electrical isolator circuit.
  24. 24. The electrical isolator circuit according to claim 22 or 23, in which the auxiliary power supply line provides electrical power to an actuated circuit of the high voltage circuit.
  25. 25. The electrical isolator circuit according to any one of claims 22 to 24, in which the electrical isolator circuit comprises a controller circuit that is operable to drive the switch and which is operable in dependence on the signal coupled by the capacitor of the DC isolator.
  26. 26. The electrical isolator circuit according to any one of the preceding claims, in which the DC isolator comprises a plurality of capacitors in parallel with each other, whereby each of a plurality of signals is coupled by a respective capacitor from the low voltage circuit to the high voltage circuit.
  27. 27. An electrical apparatus comprising the electrical isolator circuit according to any one of the preceding claims.
  28. 28. The electrical apparatus according to claim 27, in which the electrical apparatus further comprises a load circuit, with power to the load circuit being provided by a power DC isolator of the electrical isolator circuit.
  29. 29. The electrical apparatus according to claim 28, in which an output from the load circuit is electrically coupled to the DC isolator such that the load circuit provides a signal to the capacitor of the DC isolator.
GB0918036A 2009-10-15 2009-10-15 An isolating capacitor using a PCB layer as a dielectric Withdrawn GB2474476A (en)

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Application Number Priority Date Filing Date Title
GB0918036A GB2474476A (en) 2009-10-15 2009-10-15 An isolating capacitor using a PCB layer as a dielectric

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GB2474476A true GB2474476A (en) 2011-04-20

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014135209A1 (en) 2013-03-06 2014-09-12 SiEVA Apparatus for high side transistor bridge driver

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4837452A (en) * 1988-10-19 1989-06-06 Spectra-Physics, Inc. Off-line dc power supply
US20090015315A1 (en) * 2007-07-12 2009-01-15 Stmicroelectronics S.A. Circuit for controlling an a.c. switch

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4837452A (en) * 1988-10-19 1989-06-06 Spectra-Physics, Inc. Off-line dc power supply
US20090015315A1 (en) * 2007-07-12 2009-01-15 Stmicroelectronics S.A. Circuit for controlling an a.c. switch

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014135209A1 (en) 2013-03-06 2014-09-12 SiEVA Apparatus for high side transistor bridge driver

Also Published As

Publication number Publication date
GB0918036D0 (en) 2009-12-02

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