Apparatus for Compensating for Resistance Tolerances of a Fuse for a Circuit and Line Driver for a Connection of a Communication Device

Abstract

An apparatus for compensating for resistance tolerances of a fuse for a circuit, wherein the apparatus is particularly intended for use in a line driver for a communication device and includes a tolerance-affected fuse, a first resistor connected in series with the fuse, and a second resistor connected in parallel with the fuse and the first resistor, where the apparatus has, at a predefined ambient temperature, a resistance that corresponds to a desired total resistance, where the resistance of the second resistor is, depending on a power input into the apparatus in a fault state and/or depending on a predefined tolerance of the resistance of the apparatus, a multiple of that of the first resistor.

Claims

1. An apparatus for compensating for resistance tolerances of a fuse for a circuit, comprising a tolerance-affected fuse; a first resistor connected in series with the fuse; a second resistor connected in parallel with the fuse and with the first resistor; wherein the apparatus has, at a predefined ambient temperature, a resistance which corresponds to a desired total resistance; and wherein the resistance of the second resistor is depending on at least one of a power input into the apparatus in at least one of a fault state and a predefined tolerance of the resistance of the apparatus a multiple of that of the first resistor.

2. The apparatus as claimed in claim 1, wherein the fuse has a tolerance, with respect to its resistance, of at least 5% at the predefined ambient temperature.

3. The apparatus as claimed in claim 1, wherein the fuse has a tolerance, with respect to its resistance, of at least 20% within a predefined temperature range.

4. The apparatus as claimed in claim 2, wherein the fuse has a tolerance, with respect to its resistance, of at least 20% within a predefined temperature range.

5. The apparatus as claimed in claim 3, wherein the fuse has a temperature coefficient of at least 0.4% per degree Kelvin within the predefined temperature range.

6. The apparatus as claimed in claim 3, wherein at least one of the first resistor and the second resistor has a tolerance, with respect to a respective resistance of at most 0.1% within the predefined temperature range.

7. The apparatus as claimed in claim 5, wherein at least one of the first resistor and the second resistor has a tolerance, with respect to a respective resistance of at most 0.1% within the predefined temperature range.

8. The apparatus as claimed in claim 3, wherein the predefined temperature range comprises at least a range between −40° C. and 80° C.

9. The apparatus as claimed in claim 5, wherein the predefined temperature range comprises at least a range between −40° C. and 80° C.

10. The apparatus as claimed in claim 6, wherein the predefined temperature range comprises at least a range between −40° C. and 80° C.

11. The apparatus as claimed in claim 1, Wherein the predefined ambient temperature is 25° C.

12. The apparatus as claimed in claim 1, wherein the resistance of the second resistor is predefined depending on a power input into the apparatus when the fuse melts.

13. The apparatus as claimed in claim 1, wherein the second resistor has a resistance value at least ten times higher in relation to the first resistor.

14. A line driver for a communication device comprising a physical layer (PHY) interface apparatus, the line driver comprising: a bridge rectifier comprising two bus-side connections and two device-side connections; a first high-pass filter arrangement which is connectable to a first transmission unit of the PHY interface apparatus of the communication device; and a second high-pass filter arrangement which is connectable to a second transmission unit of the PHY interface apparatus of the communication device; wherein the first high-pass filter arrangement and the second high-pass filter arrangement each comprise an apparatus as claimed in claim 1.

15. The line driver as claimed in claim 14, wherein the line driver is integrated into a communication device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention is explained in more detail below using an exemplary embodiment with reference to the drawing, in which:

[0016] FIG. 1 shows a resistor network for an apparatus for compensating for resistance tolerances of a fuse for a circuit in accordance with the invention; and

[0017] FIG. 2 shows a communication device for a 2-wire Ethernet bus system, which is established for high data transmission rates with simultaneously high supply power in accordance with the invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0018] The resistor network R1 shown in FIG. 1 for compensating for resistance tolerances comprises, as well as a tolerance-affected fuse F, a first resistor R.sub.S, which is connected in series with the fuse, and a second resistor R.sub.P, which is connected in parallel with the fuse F and with the first resistor R.sub.S. The resistor network R1 has, at a predefined ambient temperature, such as 25° C., a resistance that corresponds to a desired total resistance.

[0019] In the present exemplary embodiment, the fuse F has a tolerance, with respect to its resistance, of at least 5% at the predefined ambient temperature. The fuse F has a tolerance, with respect to its resistance, of at least 20% within a predefined temperature range, such as from −40° C. to 80° C. Without compensation, this would result in significant tolerances of the resistance of a resistor network comprising the fuse F, in particular if the fuse has, within the predefined temperature range, a temperature coefficient of 0.4% per degree Kelvin or higher.

[0020] The resistance of the second resistor R.sub.P is selected depending on a power input into the resistor network R1 in a fault state and/or depending on a predefined tolerance of the resistance of the resistor network R1, and is a multiple of that of the first resistor R.sub.S. Preferably, the resistance of the second resistor R.sub.P is predefined depending on a power input into the resistor network R1 when the fuse F melts, such that the first resistor R.sub.S can be established with an appropriately low value. In relation to the first resistor R.sub.S, the second resistor R.sub.P may have, for example, a resistance value at least ten times higher. A configuration according to which, within the predefined temperature range, the first resistor R.sub.S and/or the second resistor R.sub.P have a tolerance, with respect to the respective resistance thereof, of at most 0.1% proves particularly advantageous for a low tolerance of the resistance of the resistor network R1.

[0021] Combining the fuse F with a parallel and a series resistor makes it possible to compensate effectively and efficiently for the tolerance of the resistance of the fuse F within the resistor network R1. This is illustrated below via several numerical examples.

[0022] If, for example, a fuse F with a resistance of between 2.5 ohms and 5 ohms at a predefined ambient temperature is used (3.75 ohms±33.3% at 25° C.) and the fuse F has a temperature coefficient of 0.6% per degree Kelvin, this results in a resistance of the fuse F of between 1.04 ohms and 6.8 ohms over an entire temperature range of from −40° C. to 105° C. This corresponds to 3.92 ohms±73.5% over the entire temperature range. If, for example, a terminating resistance of 50 ohms is required for a signal line, then the tolerance of the resistance of the fuse F can already be compensated for to a limited extent via a first resistor R.sub.S with a value of 46.25 ohms (50 ohms-3.75 ohms) and a tolerance of ±1% over the entire temperature range. This results, depending on batch and temperature range, in a total resistance of between 46.83 ohms (1.04 ohms+46.25 ohms*99%) and 53.51 ohms (6.8 ohms+46.25 ohms*101%). This corresponds to a total resistance of 50 ohms±7.02% over the entire temperature range.

[0023] Additional compensation for the tolerance of the resistance of the fuse F is achieved if a second resistor R.sub.P in parallel with a series circuit consisting of the fuse F and the first resistor R.sub.S is additionally used. If, for example, a first resistor R.sub.S with a value of 52 ohms±1% (over the entire temperature range) and a second resistor R.sub.P with a value of 510 ohms±1% (over the entire temperature range) are used, this then results in a minimum total resistance of 47.57 ohms (1/(1/510 ohms*99%+1/(52 ohms*99%+1.04 ohms))) and a maximum total resistance of 53.19 ohms (1/(1/510 ohms*101%+1/(52 ohms*101%+6.8 ohms)). This corresponds to a total resistance of 50.26 ohms±5.85% over the entire temperature range. In comparison with the series circuit consisting of the fuse F and the first resistor R.sub.S, this results in the tolerance of the total resistance being reduced by 1.18%. In addition, if the fuse F melts, then the second resistor R.sub.P with a value of 510 ohms means that a sufficiently high total resistance remains for limiting the current or power in potentially explosive environments.

[0024] If a first resistor RS with a value of 47.5 ohms±1% (over the entire temperature range) and a second resistor R.sub.P with a value of 2 kiloohms±1% (over the entire temperature range) are used, then the tolerance of the total resistance is increased to ±6.72%. However, there is a reduction in the power input into the resistor network R1 if the fuse F melts. Conversely, if a first resistor RS with a value of 71.5 ohms±1% and a second resistor R.sub.P with a value of 150 ohms±1% are used, then the tolerance of the total resistance is reduced to ±3.61%. However, in this case, there is an increase in the power input if the fuse melts. It has to be weighed up on a case-by-case basis how much power input into the resistor network R1 in the fault state or if the fuse melts should be permissible. The resistor network R1 can be dimensioned accordingly.

[0025] The resistor network R1 shown in FIG. 1 is preferably used in a line driver of a communication device for a 2-wire Ethernet bus system of FIG. 2. The resistor network R1 forms in each case a low-value resistor that is protected by the fuse F and is comprised of a first high-pass filter arrangement H1 and a second high-pass filter arrangement H2, respectively. The two high-pass filter arrangements H1-H2 are connected to a first and a second transmission unit TX, respectively, of a PHY interface apparatus PHY of the communication device. Moreover, the two high-pass filter arrangements H1-H2 each comprise a high-value resistor R2 and a capacitor arrangement C with at least two series-connected capacitors.

[0026] In the present exemplary embodiment, the communication device is configured in accordance with Ethernet Advanced Physical Layer and has a bridge rectifier that comprises four rectifier diodes D1-D4, two bus-side connections B1-B2 and two device-side connections T1-T2. In particular, the communication device comprises a bus input for connection to multiplexed supply lines of the 2-wire Ethernet bus system, which are configured to transmit energy and data simultaneously. The bus input is formed by the bus-side connections B1-B2 of the bridge rectifier.

[0027] The PHY interface apparatus PHY is intended for coding and decoding data interchanged between the communication device and the 2-wire Ethernet bus system. The PHY interface apparatus PHY is connected to a cathode of a diode D via the first high-pass filter arrangement H1, and to the second device-side connection T2 of the bridge rectifier via the second high-pass filter arrangement H2. In particular, the PHY interface apparatus PHY is configured for differential data signal transmission and therefore comprises two transmission units TX and two reception units RX.

[0028] The low-value resistors R1 of the high-pass filter arrangements H1-H2, which resistors are each formed by a resistor network in accordance with the disclosed embodiments, are each connected to a transmission unit TX and to the respective capacitor arrangement C. By contrast, high-value resistors R2 are each connected to a reception unit RX and to the respective capacitor arrangement C. The capacitor arrangement C of the first high-pass filter arrangement H1 is connected to the cathode of the diode D, while the capacitor arrangement C of the second high-pass filter arrangement H2 is connected to the second device-side connection T2 of the bridge rectifier. Preferably, the low-value resistors R1 have an impedance of 50 ohms, and the high-value resistors R2 have an impedance of 2-5 kiloohms.

[0029] As shown in FIG. 2, an anode of a first rectifier diode D1 is connected to a first bus-side connection B1, while a cathode of the first rectifier diode D1 is connected to a first device-side connection T1. Similarly, an anode of a second rectifier diode D2 is connected to a second bus-side connection B2, while a cathode of the second rectifier diode D2 is connected to the first device-side connection T1. Moreover, a cathode of a third rectifier diode D3 is connected to the first bus-side connection B1, while an anode of the third rectifier diode D3 is connected to a second device-side connection T2. Furthermore, a cathode of a fourth rectifier diode D4 is connected to the second bus-side connection B2, while an anode of the fourth rectifier diode D4 is connected to the second device-side connection T2.

[0030] The communication device additionally comprises a power supply unit PSU, which is connected, via a first coil L1, to the cathode of the diode D, the anode of which is connected to the first device-side connection T1 of the bridge rectifier. The power supply unit PSU is connected to the second device-side connection T2 of the bridge rectifier via a second coil L2. The power supply unit PSU is formed as a DC voltage power supply unit, and is connected to the first coil L1 via a first power supply unit connection P1, while a second power supply unit connection P2 is connected to the second coil L2. The two coils L1-L2 form a low-pass filter arrangement for the power supply unit PSU. The two coils L1-L2 are each connected to the power supply unit PSU without any additional freewheeling diode arrangements connected in parallel therewith.

[0031] Depending on a connection of the communication device to the 2-wire Ethernet bus system, a freewheeling diode arrangement for the two coils L1-L2, which comprises in three diodes each arranged in series, is formed either by the first rectifier diode D1, the diode D and the fourth rectifier diode D4, or by the second rectifier diode D2, the diode D and the third rectifier diode D3. Preferably, the bridge rectifier is established for use in an intrinsically safe circuit and has a safe connection to inductors to be protected, namely the coils L1-L2, in accordance with IEC60079-11.

[0032] In accordance with an alternative embodiment, which is not explicitly shown in the figures, the power supply unit PSU is connected, via the first coil L1, directly to the first device-side connection T1 of the bridge rectifier rather than to the diode D. Here, the diode D is connected to the bridge rectifier on the bus input side rather than on the device side. In this case, the anode of the diode D is connected to a first bus connection of the communication device, while the cathode of the diode is connected to the first bus-side connection B1 of the bridge rectifier. In the alternative embodiment, the second bus-side connection B2 of the bridge rectifier forms a second bus connection of the communication device. The two bus connections of the communication device are not interchangeable in the alternative embodiment.

[0033] In the present exemplary embodiment, the bridge rectifier, the diode D, the first coil L1, the second coil L2, the first high-pass filter arrangement H1 and the second high-pass filter arrangement H2 form a line driver integrated in the communication device. In principle, a line driver of this kind may also be formed as an external or separate device and can be used to upgrade existing communication devices for high data transmission rates with a simultaneously high supply power. In the case of applications of this kind, coils associated with a power supply unit are also always protected via a total of three diodes in series.

[0034] Thus, while there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the methods described and the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.