Flexible flat cable with integrated output filter

The present invention relates to a flexible flat conductor having at least two electrically conductive layers, which are at least partially surrounded by an electrically insulating sheath, wherein the electrically conductive layers are insulated from each other by at least one dielectric layer arranged between them.

Furthermore, the invention relates to a power supply having such a flexible flat conductor.

Power supplies and chargers in the low power range are now designed as a switch mode power supply due to wide input voltage range requirements and lower losses. Widely used is the embodiment of a plug-in power supply unit 1, in which an electronic circuit for power conversion is arranged in a housing attached directly to the power plug, as shown in FIG. A variety of such devices is used to charge portable devices such. B. Mobile phones, PDAs, CD / DVD / MD / MP3 players and the like used. In particular, the size of the charger, its weight and the ease of transport play an important role in portability. The connection to the consumer (not shown in the figure) is usually carried out via an output plug 2 and a two-pole output line 3, which is designed as a round line or twin line, as shown in Figure 1.

Furthermore, it is known to use in such network devices flat cable, which are provided with a winding device. An example of such an arrangement is shown, for example, in JP 2001/128350 and WO 01/21521 A1. Such arrangements allow a particularly space-saving and orderly storage of the cable during transport.

For power conversion today usually a flyback converter, which is preferred due to the low circuit complexity in this power range. If the energy transmission takes place by means of a primary control, as shown in DE 100 18 229 A1, there is only one diode for rectification on the secondary side and an LC filter for filtering the output voltage. A circuit diagram of such a known output-side circuit is shown in Figure 2. While a ceramic capacitor is usually used for the capacitor C2 shown in FIG. 2, an electrolytic capacitor is usually selected due to the requirements for a low equivalent series resistance with a minimum cost for the capacitor C1. The components shown in Figure 2 typically have the following characteristics:<ul id="ul0001" list-style="none" compact="compact"><li>C1: 22 μF ... 470 μF</li><li>L: 1 μH ... 100 μH</li><li>C2: 10 pF ... 10 μF</li></ul>

As further shown in FIG. 3, a common-mode choke L3 'is usually connected downstream with a filter capacitor C3 to suppress common-mode noise. However, the filter arrangements shown in FIGS. 2 and 3 require considerable space as conventional discrete components in the power supply unit and therefore counteract further miniaturization of the power supply unit. In addition, high-frequency disturbances can also be coupled in via the output line, which usually require an additional input filter in the consumer and therefore increase the size, weight and cost of the consumer.

Finally, it is known to realize filter structures as simply as possible in a cost-effective and space-saving manner, to produce them in an integrated construction with a flexible flat conductor. Japanese Laid-Open Patent Publication JP 06-139831 A discloses a flexible flat cable having electronic components integrated therein. In this case, different conductive structures, which are surrounded by an electrical insulation, insulated from each other by a further dielectric layer, so that a capacitance is formed. By means of a meander-shaped structuring of the conductor planes, an inductance can be realized after a subsequent folding process in which the individual meanders in the third dimension are stacked in a leporello-like manner. The combination of capacitance and inductance provides an integrated filter here.

A disadvantage, however, in this solution, that in order to form the required inductance for a filter structure, the flexible flat conductor must be folded several times in a defined manner, which also requires an increased space required in addition to an increased effort in production. In addition, the required folding of the flexible flat conductor according to JP 06-139831 A requires that only certain areas of the flexible flat conductor can be used for the integrated filter structure, but long stretches of the cable must remain unused.

It is therefore an object of the present invention is to provide an improved flexible flat conductor and a power supply unit with such a flat conductor, in which the filtering can be improved, the space requirement can be reduced and at the same time the manufacturing cost can be reduced.

This object is achieved by a flexible lead with the features of claim 1 and a power supply with the features of claim 10. Advantageous developments of the present invention are the subject of several subclaims.

The solution according to the invention is based on the knowledge that a particularly simple and space-saving realization of a filter structure can be achieved by an integrated arrangement, wherein at least one of the electrically conductive layers of the flexible flat conductor is structured by recesses, that a plurality of meandering elements is formed, and in which the meandering elements are serially connected in a plane defined by the flat conductor, to form the filter structure. Cost-intensive process steps, such as folding the flat conductor, are eliminated in this solution. Furthermore, the flexibility in designing, for example, an output filter in a power supply is substantially increased because the entire length of the line can be used for the filter. The flexibility of the cable is maintained over the entire length, and it can be used without problems, for example, a winder. For this purpose, a flexible ceramic dielectric is preferably embedded between the electrically conductive layers.

According to an advantageous development, the recesses occupy less than 50% of the area of ​​each meander element. This allows a sufficiently high inductance can be achieved with only slightly increased DC resistance. Also, the required capacity can be produced without problems.

In particular, when the recesses are formed by slots extending across about 50% of the width of the first conductive layer transverse to the longitudinal axis of the lead and even have a width of less than 10% of their length, the increase in DC resistance remains on the order of less than 1.5%.

According to an advantageous development of the present invention, the dielectric layer is subdivided by at least one recess into individual subregions. As a result, different series or parallel connected capacities can be realized in an advantageous manner.

Thus, for example, the Π filters can be formed via a corresponding circuit of the meander structures in the first electrically conductive layer, as required, for example, according to FIG.

More complex filter structures can furthermore be realized by providing recesses both transversely to the direction of the longitudinal axis of the flexible flat conductor and in the direction of the longitudinal axis in the dielectric layer. This can be realized in a very cost effective manner a variety of required filter structures.

If a further of the electrically conductive layers is also structured by forming meander structures, counter and common mode filters can be realized. This can be achieved in a very simple manner in that the meander structures are either arranged in the same direction (whereby a push-pull filter can be realized) or are arranged in opposite directions, whereby a common mode filter is formed.

The advantageous properties of the flexible flat conductor according to the invention are particularly useful if it is used in a power supply with a primary-side connector and a secondary-side connector between the secondary-side connector and the actual power supply as output line. Such a power supply on the one hand has the advantage that the space required for the filter structures in the power supply can be drastically reduced, and that on the other hand, the system costs in the consumer, so the mobile device can be lowered because an input filter can be avoided. Furthermore, the functionality of the output filter can be adapted to the needs of the power supply in a very space-saving and cost-effective manner.

The power supply according to the invention can also be equipped with a winding device to at least partially roll up the flexible flat conductor, for example, for the transport or for shortening the output cable.

With reference to the advantageous embodiments shown in the accompanying drawings, the invention will be explained in more detail below. Similar or corresponding details of the subject invention are provided with the same reference numerals. Show it:<dl id="dl0001"><dt>FIG. 1</dt><dd>a perspective view of a plug-in power supply according to the prior art;</dd><dt>FIG. 2</dt><dd>a circuit diagram of a secondary-side filter assembly;</dd><dt>FIG. 3</dt><dd>another secondary-side filter structure;</dd><dt>FIG. 4</dt><dd>a cross section through the flexible flat conductor according to the invention;</dd><dt>FIG. 5</dt><dd>a schematic representation of the flexible flat conductor of Figure 4 in plan view;</dd><dt>FIG. 6</dt><dd>a plan view of the flexible flat conductor according to the invention according to a first embodiment;</dd><dt>FIG. 7</dt><dd>a schematic representation of a single meander structure of Figure 6;</dd><dt>FIG. 8</dt><dd>a schematic representation of a flexible flat conductor according to a second advantageous embodiment;</dd><dt>FIG. 9</dt><dd>a schematic representation of a flexible flat conductor according to a third advantageous embodiment;</dd><dt>FIG. 10</dt><dd>a schematic representation of a flexible flat conductor according to a fourth advantageous embodiment;</dd><dt>FIG. 11</dt><dd>an electrical equivalent circuit diagram of the arrangement of Figure 10;</dd><dt>FIG. 12</dt><dd>a generic stage of the equivalent circuit of Figure 11;</dd><dt>FIG. 13</dt><dd>a transfer function for a 10, 20 or 30-stage filter of Fig. 12;</dd><dt>FIG. 14</dt><dd>an electrical equivalent circuit diagram of the arrangement of Figure 5;</dd><dt>FIG. 15</dt><dd>an electrical equivalent circuit diagram of an RCLC filter;</dd><dt>FIG. 16</dt><dd>the transfer functions of the filter structures of Figures 14 and 15;</dd><dt>FIG. 17</dt><dd>various transfer functions of the structure of Fig. 15;</dd><dt>FIG. 18</dt><dd>a flexible flat conductor according to another embodiment;</dd><dt>FIG. 19</dt><dd>the electrical equivalent circuit diagram of the structure of Figure 18;</dd><dt>FIG. 20</dt><dd>a further advantageous embodiment of the flexible flat conductor according to the invention;</dd><dt>FIG. 21</dt><dd>the equivalent circuit of the arrangement of Figure 20;</dd><dt>FIG. 22</dt><dd>the perspective view of a power supply with a flexible flat conductor according to the invention.</dd></dl>

FIG. 4 shows a cross section through a flexible flat conductor 100 according to the invention. The flexible flat conductor 100 has two electrically conductive layers 102 and 104, which are surrounded by an electrically insulating sheath 106. According to the invention, in order to integrate the function of a filter into the flexible flat conductor 100, the two electrically conductive layers 102, 104, which may be made of copper or aluminum, for example, are separated from one another by a dielectric 108. Initially, without further structuring of the metallic layers 102 and 104, a capacitance is formed between the conductors, which is calculated according to the following equation [1].<maths id="math0001" num="[1]"><math display="block"><mrow><msub><mrow><mtext>C = ε</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>ε</mtext></mrow><mrow><mtext>r</mtext></mrow></msub><mtext> A / d</mtext></mrow></math><img file="EP1544867A2_D0001.tif" /></maths>

As a dielectric is preferably a flexible ceramic dielectric with a dielectric constant of ε_r = 100 to 5000 embedded between the two layers of metallic conductors 102, 104 and laminated together with two outer insulating films 106.

According to an advantageous embodiment, an output line according to the invention may have two meters total length and a cross section of 2 x 0.25 mm² respectively. The geometric and electrical parameters may, for example, assume the following values: width of the copper foil 7 mm, thickness of the copper foil 35 μm, thickness of the dielectric layer 5 μm, relative dielectric constant ε_r = 1000 and thickness of the insulating film 25 microns.

In order to achieve a uniform lamination of the outer insulation layers 106, the resulting total width of the line 100 is 7.5 mm, with a thickness of only 0.125 mm. These dimensions are particularly suitable for a space-saving winding when using the flexible flat conductor 100 in a power supply, as shown in Figure 22. The space requirement compared to a conventional round cable (as shown for example in Figure 1) is reduced by 22%.

With the example values ​​of the parameters given above, a resulting total capacitance between the two conductors 102 and 104 of approx. 25 uF. In switching power supplies with a switching frequency of, for example, 100 kHz, this value is sufficient to obtain a sufficient screening of the output voltage. Furthermore, the ceramic dielectric 108 has better high-frequency properties, in particular a lower equivalent series resistance (ESR) than a comparable electrolytic capacitor, so that despite the comparatively small capacity, a sufficiently low voltage ripple is achieved at the end of the line. In addition, due to the areal distribution of the capacitance over the entire surface of the line in conjunction with the very good heat transfer through the copper electrodes, a slight self-heating of the flexible flat conductor 100 also results at high currents through the dielectric.

According to the invention, the first of the two electrically conductive layers 102 is structured such that a meandering structure is formed, as shown in FIG. According to the first embodiment of the present invention, the opposing copper foil 104 remains unstructured. As a result, an inductance parallel to the capacitor, the value of which can be calculated approximately from the formula for a flat square coil with one turn, is formed.

According to the invention, individual meandering elements 110 are serially connected in series in the plane of the flexible flat conductor in order to produce the required inductance.

In the meandering structure shown in FIG. 6, which consists of a series of meandering elements 110, each formed by relatively small recesses 109, 111 in area, the inductance required for an integrated filter can be produced in an elegant manner only within the plane of the flexible flat conductor without needing, for example, a folding as shown in JP 06-139831. In this way, if necessary, the entire length of the flexible flat conductor for the corresponding inductance can be provided with meandering elements 110. However, this is not absolutely necessary, but depends on the respectively required parameters.

With reference to FIG. 7, now approximately the inductance achieved is to be calculated. In this case, it is assumed that the inductance of the individual meander element 110 shown in FIG. 7 is characterized by the basic geometry of a flat square coil with only one turn, which has a turn diameter a and a trace width w. The inductance L of such a meandering element 110 can then be calculated according to the following equation [2]:<maths id="math0002" num=""><img file="EP1544867A2_D0002.tif" /></maths>

The individual meander element 110 of FIG. 7 is characterized in that it is formed by a comparatively small slot 109 in the electrically conductive material of the conductor track 102. Between the individual meandering elements 110, slots 111, which in the embodiment shown have the same dimensions as the slots 109, are arranged. For example, the slot may have a length of about 3.5 mm and a width of only 0.2 mm. With an edge length a of 7 mm, the remaining strip width w is therefore 3.4 mm. Inserting these two values ​​into the equation [2], a single meander element 110 with the dimensions mentioned has an inductance of about 9 nH. The thickness t of the metallization was assumed to be 35 μm for this calculation.

A juxtaposition of meandering elements 110 over the entire length of the flexible flat conductor of two meters would thus lead to an inductance of 2.5 μH. Due to the special geometry of the meander elements, the DC resistance increases only insignificantly by about 1.4%.

FIG. 8 shows a further advantageous embodiment of the present invention. If the dielectric 108 is interrupted by a slot 112 arranged transversely to the longitudinal axis of the flexible flat conductor, two partial regions A1 and A2 result (for better clarity, the structured layer 102 is shown in a raised position). As an equivalent circuit of the structure in FIG. 8, the Π-filter of FIG. 2 results.

By shifting the slot 112 along the longitudinal dimension of the flexible flat conductor 100 at a constant inductance, any distribution of the total capacitance can be achieved. With the dimensions mentioned above, every millimeter of length stands for a capacity of approx. 10 nF. Due to the manufacturing tolerances, the minimum dimension of one of the dielectric surfaces A1, A2 should not be less than approximately 1 mm.

As a filter capacitor in mobile telecommunications equipment, such as mobile phones, a small capacity is particularly desirable at the cable end to prevent coupling of the carrier in the megahertz frequency range. This can be achieved by an additional slot 114 extending in the direction of the longitudinal axis of the flexible flat conductor 114 in the dielectric 108. This further embodiment is shown schematically in FIG. This results in two single capacitors with half capacity, symbolized by the areas A3 and A4, which are connected in series via the backside metallization 104. This results in a resulting capacity of approx. 2.5 nF. Assigning the cross section 114 asymmetrically, so that, for example, the area A3 is equal to 1/6 A4, it follows from equation [3] as the resulting capacity:<maths id="math0003" num=""><img file="EP1544867A2_D0003.tif" /></maths>

A minimal capacity in the context of today's usual design rules results when one makes several transverse slots 114 so wide that only three dielectric surfaces of 1 mm x 1 mm remain. This results in a total capacity of approx. 100 pF in the series connection.

A significant advantage of the present invention is that this capacitance is very close to the consumer and that thus interference frequencies that couple via a conventional line, are far more effectively suppressed. This may optionally be dispensed with in the consumer on an additional filtering, and the consumer can be made easier and cheaper.

By choosing different longitudinal and transverse strips 112, 114, one can generate arbitrary filter combinations lying within the maximum capacitances and inductances. Even multi-stage filters are possible.

Figure 10 shows a flexible flat conductor 100, in which such a multi-stage filter is integrated. The associated electrical equivalent circuit diagram is shown in FIG.

To illustrate the many possibilities in the design of the filter characteristic, the filter of Figure 11 is decomposed into corresponding generic stages. For each stage, a longitudinal inductance of 9 nH with an ohmic resistance of approximately 100 mΩ and a transverse capacitance Ci of 85 nF is assumed. FIG. 12 schematically shows the generic stage "i".

FIG. 13 shows the transfer functions for flexible flat conductors with 10, 20 and 30 stages. Reference numeral 116 denotes the curve for 10 generic stages of FIG. 12, the curve 118 the transfer function for 20 stages and the curve 120 the transfer function for 30 stages. As can be seen from FIG. 13, when the number of stages is increased, the cutoff frequency remains constant, only the filter steepness increases. In a frequency range of less than 100 kHz, the filter effect is rather low.

If the flexible flat conductor does not have a meandering structure in the electrically conductive layer 102, 104, that is, if the inductance is negligible, only the capacitance is effective and a simple RC filter results, as shown in FIG. The total achievable capacity over a length of 2 m is C1 = 25 μF.

In order to improve the high-frequency properties, a further LC circuit can be connected downstream of this arrangement by structuring the flexible flat conductor only in the immediate vicinity of the consumer. This produces the RCLC filter shown in FIG. 15 as an equivalent circuit diagram. The transfer functions of the filter structures of Figure 14 and Figure 15 are shown in Figure 16 as a function of the frequency. Curve 122 denotes the transfer function of the simple RC filter from FIG. 14 and curve 124 the transfer function of the RCLC filter according to FIG. 15. As seen from curve 124, the RCLC filter resonates at about 5.5 MHz. This is the resonant frequency of the LC circuit. At about 8 MHz, the attenuation is better than the simple RC filter. By varying the values ​​for the LC filter, the cut-off frequency (and therefore the high-frequency damping properties) can be influenced.

FIG. 17 illustrates various transfer functions of the filter of FIG. 15 with a variation of the values ​​for the capacitance C2. At this time, the value of the capacitance C2 was changed in the range of 50 nF to 200 nF in 50 nF steps. The cutoff frequency decreases as the value of C2 increases. In an analogous manner, this can be achieved by a variation of the inductance L1. In FIG. 17, the curve 126 denotes the transfer function for C2 = 50 nF, the curve 128 the transfer function for C2 = 100 nF, the curve 130 corresponds to C2 = 150 nF and the curve 132 to a value of C2 = 200 nF.

A further increase in the inductance can be obtained by patterning both conductor surfaces 102, 104 on the top and bottom of the dielectric 108 in meandering fashion. So you can double the inductance with full utilization of the length again.

Obtained on the appropriate length a push-pull filter (also referred to as differential mode filter), as shown in Figure 18, in which achieved with the above Parametem an effective capacity of up to 22 uF and an effective inductance of up to 7 uH can be. This design results when the two conductor surfaces congruent, that is structured with coiled meander elements 110 arranged in the same direction.

The equivalent circuit diagram corresponding to the arrangement of FIG. 18 is shown in FIG.

On the other hand, if the two conductor surfaces 102, 104 are mirror-inverted, as shown in FIG. 20, so that the meandering elements 110 are respectively arranged in opposite directions, a common mode filter is obtained whose equivalent circuit diagram is shown in FIG. Thus, the same direction disturbances can be extinguished by the opposing fields of the two inductors on the top and bottom.

In a particularly advantageous manner, the flexible flat conductor according to the invention for a power supply unit, as shown in Figure 22, are used. In this case, the flexible flat conductor is used as the output line 203, which establishes the connection between the actual power supply 201 and an output plug 202. The output plug 202 may, as indicated in Figure 22, be connected to a plurality of different loads 205 (eg, cell phones, PDAs, CD / DVD / MD / MP3 players, and the like) to provide them with electrical power. The power supply 201 has, in the illustrated embodiment, a winding device 204 which may be constructed, for example, similar to that shown in Japanese Patent Laid-Open Publication No. 2001/128350. The cover of the power supply 201 is shown in dashed lines in Figure 22, so as not to jeopardize the clarity.

With the flexible flat conductor according to the invention as the output line 203 can be realized within the given geometry of this output line, the most diverse filter arrangements. This results in the power supply 201 in addition to the reduced dimensions of the line arrangement, especially a space and cost reduction in the power supply. But even in a not shown here with the connector 202 to be connected terminal space and cost can be reduced, as can be dispensed with a separate input filter. The planar structure of the flexible flat conductor according to the present invention results in low tolerance deviations with high reproducibility and easier manufacturability. That is, the filter structures can be formed with a high degree of reproduction.

Finally, the solution according to the invention allows the use of environmentally compatible materials without additional plasticizers.