EP2797091A1 - Transformateur et alimentation utilisant un tel transformateur - Google Patents

Transformateur et alimentation utilisant un tel transformateur Download PDF

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Publication number
EP2797091A1
EP2797091A1 EP13165415.4A EP13165415A EP2797091A1 EP 2797091 A1 EP2797091 A1 EP 2797091A1 EP 13165415 A EP13165415 A EP 13165415A EP 2797091 A1 EP2797091 A1 EP 2797091A1
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EP
European Patent Office
Prior art keywords
transformer
shield
primary
winding
copper
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.)
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Application number
EP13165415.4A
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German (de)
English (en)
Inventor
Humphrey De Groot
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.)
NXP BV
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NXP BV
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Publication date
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Priority to EP13165415.4A priority Critical patent/EP2797091A1/fr
Publication of EP2797091A1 publication Critical patent/EP2797091A1/fr
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/28—Coils; Windings; Conductive connections
    • H01F27/288—Shielding
    • H01F27/2885—Shielding with shields or electrodes

Definitions

  • This invention relates to transformers, and to power supply circuits using transformers.
  • a power supply is a part of system which supplies the other components of the system with energy.
  • EMC electrospray chrometic microporescence
  • This invention relates particularly to EMC emission standards.
  • Every alternating source (current or voltage) will generate radiated noise via different kinds of medium (air or copper wire). This emission has to be limited to prevent other apparatus from being disturbed in their operation. The way the disturbance has to be measured and the maximum allowed level of disturbance can be found in the specific standards.
  • the noise which an apparatus and specifically a power supply emits can be split into common mode noise and differential mode noise. For both types, different measures have to be taken to restrict this emission. Therefore in a power supply a number of components can be found which do not contribute to the fundamental functionality but are only present to fulfil EMC regulations.
  • Figure 1 shows that the mains input is coupled to an overvoltage protection varistor 10, a common mode filter 12 and a differential mode filter 14 before application to a switch mode power supply (SMPS).
  • the SMPS the provides the power supply to the application 18, and includes a transformer providing galvanic isolation.
  • the various units are used to fulfil the EMC requirements of overvoltage protection, CM-filtering and differential-mode filtering.
  • This galvanic isolation provided by the SMPS is needed to prevent a conductive connection between the mains and the real application.
  • a transformer is used with a primary winding connected with the mains and a secondary winding connected with the application.
  • An alternating source is needed to transport energy from the primary side to the secondary side, but noise is also transported. Even though there is no conductive connection between the primary and secondary side, noise can be transported to the secondary side by the parasitic capacitance which is present between the primary and secondary side.
  • i cap is the capacitive current
  • C 1 is the size of the capacitance
  • V c1 is the voltage over the capacitance.
  • This formula shows that the amplitude of the capacitance current which is responsible for the noise is a product of the capacitance and rate of change of the capacitance voltage.
  • the emission is measured via a line impedance stabilisation network (LISN), and the converter has a passive load of 5V 1A.
  • Plot 20 represents the peak measurements and plot 22 represents the average measurements.
  • the lines 24 represent the peak and average limits imposed by standards. It is noted that the lines 24 appear in Figure 3 , 4 , 8 and 10 , but an explanation of these lines is not repeated.
  • the standards require measurement at certain frequencies.
  • the construction of the transformer is shown in the right part of Figure 2 as a cross section through the bobbin.
  • the transformer has two auxiliary windings (Aux 1 and Aux 2), a primary (P) and a secondary winding (S).
  • the auxiliary windings used to generate voltages for internal use by the power supply, such as the supply for the the primary controller.
  • the noise level is above the limit lines 24 and therefore does not meet EMC requirements.
  • the secondary side is connected to the environment, and therefore the capacitance to the environment is taken as infinite large.
  • One of the basic solutions is to place a capacitor between the secondary and primary ground to offer a return path for the noise.
  • CM common mode
  • this additional capacitance is prohibited or may only be extremely small such as in medical applications.
  • Examples of minimizing the capacitance include restricting the contact area between the primary and secondary windings or increasing the distance between the primary and secondary windings. Examples of minimizing the contact area include not using a sandwich construction or minimizing the number of wires.
  • Examples of increasing the distance include using a resonant topology with separated chambers for the primary and secondary windings (although for a flyback converter this is not really an option).
  • Another option is to restrict the voltage rate of change. By using copper shields or by clever constructions of the windings this can be realized.
  • Figure 4 shows a modification to the transformer arrangement of Figure 2 in which a copper shield 40 is provided between the primary and secondary windings, and Figure 4 also shows the resulting change in EMC performance.
  • the power supply fulfils the emission requirements to 30MHz.
  • Figure 5 shows a first example of transformer structure which is based on choosing the right sequence of windings to minimise the voltage difference. For example, with respect to the primary winding P, the turns close to the drain voltage will vary more in voltage than the turns close to the bus voltage. This is shown in Figure 5 by the waveforms. Thus, by placing the appropriate turns from the primary P and secondary S windings opposite each other the voltage difference can be minimized and therefore the noise current.
  • an alternative is to apply between the primary P and secondary S winding an additional winding 60 with the same polarity (voltage variation) as the secondary winding S but connected to the Vbus voltage on the primary side.
  • the additional winding acts as shield.
  • the capacitance on the primary side will be larger but the voltage difference between the primary and secondary sides will be almost zero.
  • a disadvantage is the increase in thickness of the total winding package and the increase in losses.
  • An alternative shielding method is to use a one turn foil instead of an additional winding.
  • the foil is less effective but is less thick.
  • the voltage difference of the last layer which is: / number of layers Vbus is replaced by: V bus / n p
  • Figure 7 shows the additional winding 60 of Figure 6 replaced with a one turn shield 70, over the full winding width.
  • a shield is made of copper foil.
  • Figure 8 shows the emission of a 5W adapter with a copper shield between the secondary and primary windings.
  • the disturbance measured by the receiver is much lower than without the shield.
  • Figure 9 the difference in dissipation is shown between a flyback converter (5V, 1A) with a transformer with shield (plot 90) and a transformer without shield (plot 92).
  • Figure 9 plots the efficiency against the output power. As can be seen, the losses increase as a result of the shield, as can be seen as a reduction in efficiency.
  • CM-choke some external filter
  • the invention provides a transformer comprising a primary winding and a secondary winding, wherein a shielding foil sheet is provided between the primary and secondary windings, comprising a material having a resistivity of more than 2 x 10 -8 ⁇ m at 20 degrees Celsius.
  • the shielding foil has a higher resistance than copper.
  • the increased resistance compared to copper results in reduced eddy current losses, while maintaining the electromagnetic shielding advantages.
  • the material can have a resistivity of more than 4 x 10 -8 ⁇ m at 20 degrees Celsius.
  • the shield has to be connected to a reference point (ground or bus voltage), so not all materials are suitable. Furthermore thin sheets have to made of the material and the material has to be flexible.
  • the material preferably comprises a copper-based alloy.
  • One example is brass such as CuZn30 brass, and another is bronze.
  • a first shielding foil sheet can be provided at the inside of the primary winding and a second shielding foil sheet of the same material can be provided at the outside of the primary winding.
  • the primary winding is provided around a bobbin, and the secondary winding is provided around the outside of the primary winding, with the shielding foil sheet between them. This provides two shielding layers which sandwich the primary winding.
  • An auxiliary winding can be provided around the outside of the secondary winding.
  • the invention also provides a switch mode power supply comprising a transformer of the invention.
  • the invention provides a transformer comprising a primary winding and a secondary winding, wherein a shielding foil sheet is provided between the primary and secondary windings.
  • the sheet comprises a material having a resistivity of more than copper.
  • the invention is based on obtaining the advantages of a foil shield but avoiding the disadvantage of a large increase of energy dissipation.
  • a foil material with a higher electrical resistivity can reduce the losses.
  • the used foil material should have good solderability for simple electrical connection of the foil to ground.
  • the electrical resistivity for these two materials at room temperature are respectively 6.25*10 -8 ⁇ m and 13.3*10 -8 ⁇ m.
  • the resistivity is 1.75 x 10 -8 ⁇ m.
  • the brass and bronze have resistivity 3.6 and 7.6 times higher than copper, so that the resistance for the same dimensions is higher by this factor.
  • Figure 10 shows the result of the spectrum when the copper shield in a transformer is replaced by a bronze shield. Compared to the spectrum in Figure 8 hardly any difference can be seen. However, the efficiency plot of Figure 11 shows an increase of approximately of 0.5% in efficiency.
  • Plot 110 is for the use of a copper shield (corresponding to plot 90 in Figure 9 )
  • plot 112 is for the use of a bronze shield
  • plot 114 is for no shield.
  • one shield is used but two shields can be used as shown in Figure 12 .
  • FIG 12 shows shields 120a and 120b between which the primary winding P is sandwiched. This arrangement of the transformer gives even more efficiency gain.
  • the foils sheet or sheets of the invention are insulated from the other windings by having a coating or by using a layer of isolation tape.
  • a higher resistivity shield such as brass or bronze
  • CM-choke superfluous or at least lower in value.
  • a shield from a conductive material with a higher resistivity than that of copper the same reduction of CM-noise can be reached as with copper but the additional losses can be lower. Therefore the efficiency of a power converter based on the transformer can be increased.
  • Copper based alloys have been given as examples. Another example is an aluminium foil, although the electrical connection is then less straightforward. Tin is a further option.
  • a shield is provided between the primary and secondary windings.
  • a shield can be provided between the different layers of turns within the primary and secondary windings.
  • the shield or shields are connected to the voltage which gives the best performance. This could be the primary ground, or the bus voltage or even an AC voltage if this gives the best result.
  • the invention can be used in all transformers used in switch mode power supplies supporting galvanic isolation.
  • CM-noise can be effectively reduced with less increase of losses.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)
EP13165415.4A 2013-04-25 2013-04-25 Transformateur et alimentation utilisant un tel transformateur Withdrawn EP2797091A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP13165415.4A EP2797091A1 (fr) 2013-04-25 2013-04-25 Transformateur et alimentation utilisant un tel transformateur

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP13165415.4A EP2797091A1 (fr) 2013-04-25 2013-04-25 Transformateur et alimentation utilisant un tel transformateur

Publications (1)

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EP2797091A1 true EP2797091A1 (fr) 2014-10-29

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3035349A1 (fr) * 2014-12-17 2016-06-22 Nxp B.V. Transformateur
US10620740B2 (en) 2015-09-18 2020-04-14 Fujitsu Limited Biometric authentication system and method
CN111180177A (zh) * 2020-01-07 2020-05-19 南京航空航天大学 一种多绕组交叠绕法高频变压器的屏蔽绕组多点接地共模噪声消除方法

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3376531A (en) * 1966-08-26 1968-04-02 Westinghouse Electric Corp Electrical inductive apparatus with wire cloth shielding means
US4308512A (en) * 1978-07-21 1981-12-29 Giorgio Capecchiacci Modular air core coil inductance assembly
EP0291093A2 (fr) * 1987-05-14 1988-11-17 Matsushita Electric Industrial Co., Ltd. Appareil à induction fixe
EP0585650A1 (fr) * 1992-08-22 1994-03-09 Robert Bosch Gmbh Transducteur et son application
EP1284487A2 (fr) * 2001-08-13 2003-02-19 Bose Corporation Blindage de transformateur

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3376531A (en) * 1966-08-26 1968-04-02 Westinghouse Electric Corp Electrical inductive apparatus with wire cloth shielding means
US4308512A (en) * 1978-07-21 1981-12-29 Giorgio Capecchiacci Modular air core coil inductance assembly
EP0291093A2 (fr) * 1987-05-14 1988-11-17 Matsushita Electric Industrial Co., Ltd. Appareil à induction fixe
EP0585650A1 (fr) * 1992-08-22 1994-03-09 Robert Bosch Gmbh Transducteur et son application
EP1284487A2 (fr) * 2001-08-13 2003-02-19 Bose Corporation Blindage de transformateur

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
"Monel alloy 400 (Ni65/Cu33/Fe2)", 1 January 2013 (2013-01-01), XP055067124, Retrieved from the Internet <URL:http://www.goodfellow.com/E/Monel-alloy-400.html> [retrieved on 20130618] *
ARNAUD DEVRED: "Service technique de cryogénie et de magnétisme", 1 January 1998 (1998-01-01), XP055067118, Retrieved from the Internet <URL:http://lss.fnal.gov/archive/other/dapnia-stcm-98-02.pdf> [retrieved on 20130618] *
HE-ZONG LI ET AL: "Analysis of microbending of CuZn37 brass foils based on strain gradient hardening models", JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, ELSEVIER, NL, vol. 212, no. 3, 11 October 2011 (2011-10-11), pages 653 - 661, XP028438582, ISSN: 0924-0136, [retrieved on 20111019], DOI: 10.1016/J.JMATPROTEC.2011.10.007 *

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3035349A1 (fr) * 2014-12-17 2016-06-22 Nxp B.V. Transformateur
CN105720823A (zh) * 2014-12-17 2016-06-29 恩智浦有限公司 变压器
US9576720B2 (en) 2014-12-17 2017-02-21 Nxp B.V. Transformer
CN105720823B (zh) * 2014-12-17 2018-07-20 恩智浦有限公司 变压器
US10620740B2 (en) 2015-09-18 2020-04-14 Fujitsu Limited Biometric authentication system and method
CN111180177A (zh) * 2020-01-07 2020-05-19 南京航空航天大学 一种多绕组交叠绕法高频变压器的屏蔽绕组多点接地共模噪声消除方法
CN111180177B (zh) * 2020-01-07 2021-02-05 南京航空航天大学 一种多绕组交叠绕法高频变压器的屏蔽绕组多点接地共模噪声消除方法

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