WO1995027344A1

WO1995027344A1 - An electronic filter

Info

Publication number: WO1995027344A1
Application number: PCT/FI1995/000173
Authority: WO
Inventors: Teijo Viljanen; Martti Sairanen
Original assignee: A. Ahlstrom Corporation; Oy Helvar
Priority date: 1994-03-31
Filing date: 1995-03-30
Publication date: 1995-10-12
Also published as: FI941542A; FI96073B; FI941542A0; FI96073C

Abstract

The present invention relates to an electronic filter (4) between a DC power supply (3) and a data transfer network (1) or the like, the data transfer network (1) utilizing a single pair of conductors (1a, 1b) as a transfer route for both signals and electric power. According to the invention the filter (4) comprises: a current generator (5), for feeding DC power into the load (2) connected to the data transfer network (1) regardless of the size of the load; a low pass filter (6), for limiting the operating frequency of the current generator (5) below the signal frequency; and a dynamics limiter (7) for monitoring the output current (Iout) of the filter (4) and the output voltage (Uout) is kept within the operating range regardless of the size of total load.

Description

An electronic filter
The present invention relates to an electronic filter, specially for use between a power supply and an automation and/or data transfer network, the filter allowing a single pair of conductors to be used for both supplying voltage to different apparatuses and for acting as a signal transfer route between the apparatuses connected to the network.

A well-known method in distributed automation and/or data transfer networks is to transmit signals by a separate pair of conductors and to supply the necessary operating voltage to each apparatus either by a separate pair of conductors or, alternatively, to provide the apparatus with its own power supply. The disadvantage of these solutions is that power must be supplied separately for each apparatus. A simple and inexpensive way of guaranteeing power supply is to use a single pair of conductors as a transfer route for both electric power and signal.

In a conventional telephone network the phones are connected to the telephone line without a separate power supply. This is done so that a reactor is arranged between the telephone exchange power supply and the telephone network. The reactor increases the output impedance of the power supply at transfer frequency. The disadvantage of this solution is that the size of the reactor depends on needed current and the signal frequencies of the telephone network. Thus, the size of the reactor structure can easily be excessive. Another disadvantage is that each telephone apparatus can be directly connected to the network as a telephone apparatus does not require much power. Further, a point worth noting is that each telephone is in principle connected to a starlike network, whereby each apparatus is fed power via one line.

Thus, this approach can not be taken with an open automation or data transfer network connecting two or more apparatuses by a single pair of conductors, as the power requirements of the apparatuses can be relatively high when compared to a telephone apparatus.

The object of the invention is to remove the above-mentioned disadvantages and to provide a new filter arrangement, especially between a power supply and an automation and/or data transfer network. The characterizing features of an electronic filter according to the invention are described in the appended claims.

An electronic filter according to the invention to be used between a DC power supply and a data transfer network or the like using a single pair of conductors as a transfer route for both signals and electric power comprises: a current generator for feeding DC power into a load connected to a network regardless of the size of the load; a low pass filter for limiting the operating frequency of the current generator below the signal frequency; and a dynamics limiter for monitoring the output current of the filter and maintaining the output voltage of the filter within operating range regardless of the size of total load.

An advantage of the invention is that by means of a filter according to the invention, any suitable power supply can be arranged into different automation and/or data transfer networks in which electric signals are transmitted and in which electric power is fed to apparatuses connected to the network.

A further advantage of the invention is that, as regards the signal, a power supply can be made to be seen as a desired impedance regardless of the direct current load of the network. Thus, when seen from the direction of the network, a filter according to the invention will not allow signal frequencies to pass. The impedance of the power supply itself is diminutive, whereby it can not be directly connected to a network.

A further advantage of the invention is that the output voltage of the filter can be controlled so that neither too low nor too high a voltage will occur in the output terminals of the filter, but the output voltage is always constant within desired limits, regardless of the output current. The allowed limits of fluctuation for the output current depend on the power supply and the load to be connected to the network.

In principle, a filter according to the invention can handle any direct current regardless of magnitude and its output voltage can be any desired DC voltage.

Yet further advantages of the invention are its simplicity of construction and thereby ease of implementation. A filter according to the invention can be arranged as an essentially bi-polar apparatus between the output terminal of the power supply and the signal and power transfer conductor of the network. A further advantage is that power losses of a filter according to the invention are small when compared with its current transfer capacity. Another advantage is that a desired line impedance can be easily achieved by means of the filter, because the output impedance of the filter itself is high on a wide frequency scale.

In the following the invention is described in more detail'by way of reference to the enclosed figures, of which
fig. 1 is schematic data transfer network via which signals and electric power can be fed to apparatuses connected to it;
fig. 2 is a block diagram representation of a filter according to the invention connected between a power supply and a data transfer network; and
fig. 3 is a practical circuit for a filter according to the invention.

A data transfer network 1 in fig. 1 comprises a pair of conductors la, lb. A plurality of apparatuses 2; 21, 22, 23, and a power supply 3 are connected to the pair of conductors la and lb by means of a filter 4 according to the invention.

Information signals are transmitted between apparatuses 2; 21, 22, 23, the signals being e.g. suitably coded messages of a certain frequency. The power supply 3 is a DC power supply and electric power is fed from it via filter 4 to the apparatuses 2; 21, 22, 23, for operating them.

An electronic filter 4 according to the invention, which in fig. 1 is connected between a DC power supply 3 and a data transfer network 1, is presented as a block diagram in fig. 2.

The filter 4 comprises a current generator 5, a low pass filter 6, a dynamics limiter 7 and a line impedance adapter 8.

The current generator 5 is connected between the input and output terminals 4a, 4b of the filter 4 for feeding suitable direct current lout into the data transfer network 1 via output terminal 4b. The lqw pass filter 6 is connected between the output terminal 4b and the current generator 5 of the filter 4, or, alternatively, between the output and input terminals 4a, 4b of the filter and over the current generator 5. The low pass filter 6 shorts signal frequencies past the current generator 5. Dynamics limiter 7, which in fact is a regulator and maintainer of the output direct voltage UOU, of the filter 4, is connected over the current generator 5, preferably only over the actual current regulating arrangement 5a.

The dynamics limiter 7 can alternatively be also connected between the output terminal 4b and ground G of the filter 4 to directly measure output voltage Uncut, and to use this as a basis for controlling current generator 5 for regulating and maintaining the output voltage Ucut.

Regardless of the total load, i.e. the number of apparatuses 2, a suitable direct current IoUt is fed into one or more apparatuses 2; 21, 22, 23 connected to the data transfer network 1 by means of the current generator 5 being a part of the electronic filter 4. The low pass filter 6 limits the operation frequency of the current generator 5 to clearly below the signal frequencies of the data transfer network 1.

The output impedance of the current generator 5 is itself very high at signal frequencies. This enables the DC power needed by the apparatuses 2 connected to the data transfer network 1 to flow unresisted, with minimal losses, through the filter 4 from the power supply 3 to the data transfer network. This DC power, i.e. output current IoUt of the filter can be varied according to the variations in the total load of the apparatuses 2 connected to the network 1. The dynamics limiter 7 is to maintain the output voltage Uout of the output terminal 4b of the filter within a pre-defined permitted range, the operation range, regardless of the total DC power load of the apparatuses 2 connected to the data transfer network 1.

The line impedance adapter 8 is arranged as a suitable output impedance adapted for the signal frequencies at the output of the filter. In this embodiment, the line impedance adapter 8 comprises a resistor 8a and a capacitor 8b connected in series, arranged between the output terminal 4b of the filter 4 and ground G. Output impedance has been chosen to be suitable for the reflection and attenuation of the signal so as to enable a noiseless operation on the signal frequencies of the network 1. When utilizing DC voltage, the line impedance is infinite, whereas on a suitable signal frequency the line impedance is preferably e.g. 50 ohms.

Fig. 3 is an advantageous circuit arrangement of an electronic filter 4 according to the invention. In this embodiment the current control arrangement 5a (fig. 2) of the current generator 5 comprises a Darlington-type pair of transistors 9, 10, the first transistor 9 of which is connected on the main current route between input terminal 4a and output terminal 4b of the filter 4 to act as the actual current regulator. The current regulation arrangement of the current generator 5 also comprises resistors 11, 12 connected between emitter and base of transistors 9, 10. The current measuring arrangement 5b (fig. 2) of the current generator 5 comprises a third resistor 13 connected on the main current route between input terminal 4a and output terminal 4b of the first transistor 9.

The feedback connection of the current generator 5 from the current measuring arrangement, i.e. resistor 13 to the second transistor 10 is accomplished by means of a resistor 14 connected between the output terminal 4b and the base of the second transistor 10. The voltage over resistor 14 corresponds to the voltage over resistors 11, 12, 13. When the voltage over the resistor 14 is maintained constant, the voltage over the second and third resistors 11, 12 is also constant. As the voltage over resistor 13 depends on the output current IoUtl the current generator 5 feeds constant current IoUt into the output of filter 4 controlled by transistors 9, 10.

In the embodiment of fig. 3 the low pass filter 6 (fig. 2) is accomplished by means of a capacitor 15 connected parallel with the feedback resistor 14 of the current generator 5.

Thus, high frequencies are shorted past resistor 14 and they can not effect the operation of the current generator 5.

The dynamics limiter 7 comprises a transistor 16 and a chain of resistors 17. The resistors 17a, 17b of the chain of resistors 17 are connected over the current regulation arrangement 5a of the current generator 5 (fig. 2) from the input filter 4a of the filter 4 to between the first transistor 9 of the current generator 5 and the current measuring arrangement, in this case the current measuring resistor 13. An intermediate point between the resistors 17a, 17b of the dynamics limiter is connected with the base of transistor 16. The emitter of the transistor 16 is connected via resistor 18 to the input terminal 4a of the filter 4 and the collector of transistor 16 is connected to the base of the second transistor 10 forming a part of the current control arrangement of the constant current generator 5.

Thus, the measuring voltage between resistors 17a, 17b, i.e. the voltage over filter 4 is used for controlling the transistor 16 and further the transistors 10, 9 of the constant current generator. This way, by measuring the voltage over filter 4 by means of the dynamics limiter 7 the output voltage Uout can be monitored and kept within the desired range regardless of the current lout passing through the filter 4.

The line impedance adapter for the fig. 3 embodiment can in principle be implemented the same way as in fig. 2.

In the above, the invention has been described by referring mainly to one advantageous embodiment, but it is clear that the invention can be modified in many ways within the inventive scope defined in the appended claims.

Claims

1. An electronic filter (4) to be used between a DC power supply (3) and a data transfer network (1) or the like, the data transfer network (1) using a single pair of conductors (la, lb) as transfer route for both signals and electric power, characterized in that the filter (4) comprises - a current generator (5) for feeding DC power into a load (2) connected to the data transfer network (1) regardless of the size of the load; - a low pass filter (6) for limiting the operating frequency of the current generator (5) below the signal frequency; and - a dynamics limiter (7) for monitoring the output current (tout) of the filter (4) and for maintaining the output voltage (UOU,) of the filter (4) within the operating range regardless of the size of total load.

2. An electronic filter according to claim 1, characterized in that the current generator (5) comprises a current measuring arrangement (5b), preferably a current measuring resistor (13), for measuring and controlling the output current (tout) of the filter (4).

3. An electronic filter according to claim 2, characterized in that the current generator (5) comprises a Darlington-type pair (9,10) of transistors as the current control arrangement.

4. An electronic filter according to claim 2 or 3, characterized in that the dynamics limiter (7) comprises a measuring circuit, such as a chain of resistors (17) for monitoring the voltage between the input and output terminals (4a, 4b) of the filter (4), and a controlling circuit, such as a transistor circuit (16), for controlling the current generator (9, 10) and regulating the output current (lout) of the filter so that voltage (UOU') of the output terminal (4b) of the filter (4) is within the desired limits regardless of the load.

5. An electronic filter according to any of claims 2-4, characterized in that the low pass filter (6) is implemented as an RC-circuit (14, 15), the low pass filter (6) being connected parallel with the current measuring arrangement of the current generator (5).

6. An electronic filter according to claim 1, characterized in that the filter (4) comprises a current generator (5) formed by a pair of transistors, preferably a Darlington-type pair of transistors (9, 10), the generator further comprising a current measuring resistor (13) and a feedback resistor (14) for regulating the current generator, the feedback resistor (14) being connected parallel with a capacitor (15) forming the low pass filter (6) together with the resistor (14), and that the dynamics limiter (7) comprises a chain of resistors (17;

17a, 17b) and a transistor circuit (16), the chain of resistors (17) being arranged over the Darlington-type pair of transistors (9, 10) of the current generator (5), and the voltage reading of the chain of resistors (17) is then used to control the transistor circuit (16), which further effects the pair of transistors (9, 10) of the current generator (5) for regulating the output current (IoU,) of the filter so that the output voltage (UOU') remains within the desired limits.

7. An electronic filter according to any of the preceding claims, characterized in that the filter (4) comprises a line impedance adapter (8) implemented as a suitable output impedance adapted for the signal frequencies at the output of the filter.