EP0535763A2 - Power supply unit - Google Patents

Abstract

In a power supply unit for data-processing systems, in particular evaluation and encoding circuits (10) of intermittent train control devices, the supply voltage for the evaluation and encoding circuits (10) arranged at the site of the track coupling coil is to be tapped from the signal circuits (1). In order to extract power from the signal circuit (1), a transformer (6) which operates according to the current transformer principle is connected with its primary winding (61) into the signal circuit (1). <IMAGE>

Description

The invention relates to a power supply unit for data processing systems, in particular evaluation and coding circuits of punctiform train control devices.

At the location of the light signals equipped with a punctiform train control device, the signal term indicated on the light signal is transmitted in coded form to the receiving coil of passing rail vehicles via a fixed track coupling coil. The information about the type of signal term displayed is taken from evaluation and coding circuits which are either remotely powered or supplied with energy induced by the vehicle driving past when the power consumption is low.

The object of the present invention is to provide a power supply unit of the type mentioned at the outset which allows the supply voltage for the evaluation and coding circuits arranged at the location of the track coupling coil to be taken from the signal circuits.

When realizing such a power supply unit, care must be taken to ensure that the additionally connected circuits are decoupled well from the signal circuits. Furthermore, the effects of the additionally connected circuits on the signal circuits (deformation of the signal current) should be as small as possible and largely independent of their power consumption and the size of the signal current. In addition, a uniform supply of the additionally connected circuits is necessary both with different values of the signal current (day / night switching) as well as with clocked current (flashing signal term). In addition, the supply voltages to be provided must meet certain quality requirements because they are used to operate data processing systems. The voltage level is therefore closely tolerated (approx. ± 5%).

The object is achieved by the features of claim 1. Advantageous embodiments of the invention are described in claims 2 to 12.

In the power supply unit according to the invention, a transformer operating according to the current transformer principle is inserted into the signal circuit. An alternating current flowing in the signal circuit creates an alternating voltage on the secondary winding of the transformer, which charges an energy storage device to a constant intermediate voltage via a rectifier arrangement and a decoupling device. From this intermediate voltage, the tightly tolerated and galvanically isolated supply voltages for operating the data-processing evaluation and coding circuits are obtained via a voltage converter device.

The controllable rectifier arrangement keeps the intermediate voltage constant within predetermined limits. In a power supply unit according to claim 2, the rectifier arrangement is short-circuited at its output connections whenever the intermediate voltage exceeds a predetermined upper limit value - because the current supplied by the transmitter and predetermined by the signal circuit is generally greater than that drawn by the consumers. All of the electricity offered by the transformer can now flow freely. If this current flow were hindered, there would be saturation phenomena in the current transformer with undesired deformations of the signal current. As long as the output connections of the rectifier arrangement are short-circuited the decoupling device separates the subsequent part of the power supply device from the energy source and the intermediate voltage gradually drops during this time. If the intermediate voltage falls below a predetermined lower limit value, the rectifier arrangement is again connected to the subsequent part of the power supply device. The output connections of the controllable rectifier arrangement are no longer short-circuited and the energy storage device is recharged. The frequency of short-circuiting the output connections of the rectifier arrangement is determined by the limit values of the intermediate voltage, by the time constant of the load and by the current supply of the signal circuit.

In addition to this periodically short-circuiting two-point regulator described above, generally customary parallel regulators are also conceivable as regulating devices for the rectifier arrangement. When using a parallel regulator as a regulating device for the rectifier arrangement, the current is controlled by a regulating element through a load resistor arranged in parallel in front of the voltage converter on the output side in such a way that the intermediate voltage remains constant. A disadvantage of this method is the useless consumption of excess power. A better solution described above is available if one takes into account that a current transformer (transformer with current impressed on the primary side) may be short-circuited on the secondary side. The load circuit of the parallel regulator can therefore be replaced by a low-loss, periodically closing switch (e.g. transistor, preferably power field-effect transistor), whose duty cycle is controlled by a control element so that the intermediate voltage remains constant. A two-point controller is then obtained, which alternately loads the supplying current source with an input resistance of the consumer or short-circuits it. In the power supply unit described in claim 3, there are thus two major advantages over the Use of a parallel regulator: The voltage drop occurring at the primary winding of the decoupling transformer is essentially determined by the resistance of the consumer on the output side and not by additional losses caused by a high-performance parallel regulator. Furthermore, the voltage drop does not increase with increasing signal current, but remains constant or decreases slightly, depending on the losses occurring in the decoupling transformer. This important property ensures constant conditions in the signal circuit even with different currents (day / night switching).

The rectifier arrangement of the power supply unit according to the invention is preferably designed as a full-wave rectifier circuit. It is then particularly advantageous to choose a rectifier bridge (claim 6) instead of a center connection of rectifier diodes. Compared to the center circuit, on the one hand only half the transformer voltage is required, on the other hand the maximum reverse voltage at a rectifier diode is only half as large as with a center circuit.

To protect against harmful overvoltages, the power supply unit can have voltage-limiting circuits (claims 9 to 11). In a power supply unit according to claim 9, the secondary AC voltage occurring at the transformer is limited by series-connected zener diodes arranged parallel to the secondary winding of the transformer. The voltage limiter circuits arranged in the power supply units respond to open outputs or defective rectifier arrangements.

• Fig. 1 ein Prinzip-Schaltbild einer Ausführungsform der erfindungsgemäßen Stromversorgungseinheit,
• Fig. 2 den Verlauf des Signalstroms und der am Übertrager auftretenden Senkundär-Wechselspannung, wobei das an den Ausgangsanschlüssen angeordnete Schaltelement geöffnet ist,
• Fig. 3 den Verlauf gemäß Fig. 2, jedoch mit periodisch betätigtem Schaltelement,
• Fig. 4 die Eingangskennlinie eines Spannungswandlers, der einen konstanten Lastwiderstand mit einer konstanten Ausgangsspannung speist,
• Fig. 5 ein Schaltbild einer weiteren Ausführungsform der erfindungsgemäßen Stromversorgungseinheit,
• Fig. 6 einen an der im Signalstromkreis angeordneten Primärwicklung des Übertragers gemessenen Spannungsverlauf.

Further advantages and details of the invention result from the following description of two exemplary embodiments with reference to the drawing and in connection with the Claims 2 to 12. It shows:

• 1 shows a basic circuit diagram of an embodiment of the power supply unit according to the invention,
• 2 shows the profile of the signal current and the secondary AC voltage occurring at the transformer, the switching element arranged at the output connections being open,
• 3 shows the course according to FIG. 2, but with a periodically actuated switching element,
• 4 shows the input characteristic of a voltage converter which feeds a constant load resistance with a constant output voltage,
• 5 shows a circuit diagram of a further embodiment of the power supply unit according to the invention,
• 6 shows a voltage curve measured on the primary winding of the transformer arranged in the signal circuit.

In Fig. 1, 1 denotes a signal circuit, in which a feed transformer 2 is connected with its tapped secondary winding 22. The feed transformer 2 lies here with the connections of its primary winding 21 on an AC network of the signal box. In the signal circuit 1, a signal lamp 3 located on the line, a variable series resistor 4 for fine adjustment of the lamp current and a current monitoring relay 5 are also connected in series.

In the signal circuit 1, a transformer 6, which operates according to the current transformer principle, is also inserted for energy extraction. For this purpose, the transformer 6 is connected with its primary winding 61 in series with the other components arranged in the signal circuit 1.

The transformer 6 is followed by a rectifier arrangement 7 with a subsequent control device 8, the exemplary embodiment shown in FIG. 1 as a rectifier bridge is executed. The control device 8 essentially consists of a control element 81 and a switching element 82. The control device shown in FIG. 1 is a two-point controller, in which a power field-effect transistor can be provided as the switching element 82 (FIG. 5). In the two-point controller 8 shown in FIG. 5, an operational amplifier is provided as the control element 81, which switches the power field-effect transistor 82 via a driver circuit 83.

The rectifier bridge 7 is connected with its input connections to the connection terminals of the secondary winding 62 of the transformer 6. Furthermore, the rectifier bridge 7 is connected via its output connections to inputs of a voltage converter device 9. The voltage converter device 9 is finally led with its outputs to a data processing evaluation and coding circuit 10.

A decoupling diode 11 is connected to the output of the rectifier bridge 7. Furthermore, an energy storage device 12 is arranged parallel to the rectifier bridge 7 and to the voltage converter device 9, which in the embodiment shown in FIG. 1 consists of two storage capacitors.

An alternating current (signal current I _S ) flowing in the signal circuit 1 produces an alternating voltage on the secondary winding 62 of the transformer 6, which charges the storage capacitors 12 to a constant intermediate voltage U _Z via the rectifier bridge 7 and the decoupling diode 11. From this intermediate voltage U _Z , the narrow-tolerance and galvanically separated supply voltages for operating the data-processing evaluation and coding circuit 10 are obtained via the voltage converter device 9.

The intermediate voltage U _Z kept constant within specified limits. Whenever the intermediate voltage U _Z exceeds a predetermined upper limit value, because the current supplied by the transmitter 6 and predetermined by the signal circuit 1 is generally greater than that drawn by the evaluation and coding circuit 10, the switching element 82 closes the rectifier bridge 7 at its Output connections short. The entire current offered by the transformer 6 can now continue to flow unhindered. If this current flow were hindered, there would be saturation phenomena in the current transformer (in the converter 6) with undesirable deformations of the signal current I _S. As long as the switching element 82 is closed, the decoupling diode 11 separates the subsequent part of the power supply device from the energy source, the intermediate voltage U _Z gradually drops during this time. The decoupling diode 11 prevents the storage capacitors 12 from discharging via the closed switching element 82. If the intermediate voltage U _Z falls below a predetermined lower limit value, the control element 81 of the control device 8 opens the switching element 82 and the storage capacitors 12 are recharged. The frequency of switching is determined by the distance between the specified upper and lower limit of the intermediate voltage U _Z , by the time constant of the load and by the current supply from the current source.

, wobei mit U_D die Diodendurchlaßspannung bezeichnet ist. Die Flanken im Bereich der Nulldurchgänge stellen Anfangs- und Endstücke von Sinushalbwellen mit sehr großer Amplitude dar, die sich bei offener Sekundärwicklung einstellen würden; das gilt jeweils immer nur solange, wie U₂(t) < Û ist - wenn also die Gleichrichterdioden der Gleichrichterbrücke 7 sperren.2 and 3 explain the mode of operation of the two-point control which is preferably used in the power supply unit according to the invention. The sinusoidal signal current I _S and the voltage curve U.sub.2 (t) occurring on the secondary winding 62 of the transformer 6 are shown in each case. When the switching element 82 is continuously open, a square-wave voltage U₂ (t) with the peak value arises at the secondary winding 62 of the transformer 6 almost in phase with the signal current I _S ${\text{Û = U}}_{\text{Z}}{\text{+ (3xU}}_{\text{D}}\text{)}$

, where U _{D is} the diode forward voltage. The edges in the area of the zero crossings represent start and end pieces of sine half-waves with very large ones Represents the amplitude that would occur with the secondary winding open; that applies only as long as U₂ (t) <Û - so if the rectifier diodes of the rectifier bridge 7 block.

In Fig. 3, the signal current I _S and the voltage generated on the secondary winding 62 of the transformer 6 U₂ (t) is shown, however, the switching element 82 is actuated periodically by the control element 81. When the switching element 82 is closed, U₂ (t) decreases to U _k . The signal current I _S changes only slightly because its amplitude is determined almost entirely by the other signal circuit elements.

ist in Fig. 6 dargestellt. Mit N bzw. T sind hierbei die Betriebspunkte bei Nachtstrom (N) bzw. bei Tagstrom (T) bezeichnet.The need for regulation in the voltage converter device 9 will be explained with reference to FIG. 4. In the case of the input characteristic shown in FIG. 4 of a DC voltage converter that feeds a constant load resistance with a constant output voltage, the sub-areas designated Ab, Nb and Ün can be distinguished from the start-up area, useful area and overvoltage area. In the start-up range (Ab) the output voltage has not yet reached its nominal value; in the useful area (Nb) there is an almost constant power consumption of the DC-DC converter; In the overvoltage range (Ü), the input current increases again with increasing input voltage because of the poorer efficiency there and because of voltage-limiting measures. When operating with a predetermined constant current I _const , which a current transformer with a downstream rectifier would supply without additional devices, three possible operating points, labeled A, B, C, are obtained in the current range of interest, of which only the operating point C is stable in the unfavorable overvoltage range turns out. In order to obtain a stable operating point B in the useful range, the DC-DC _converter must be operated with a constant input voltage U _Econst instead of with the given current I _const . The one for this new working point B belonging converter input current I _EB is generally smaller than the current offered by the current source. A control device 8 to be inserted between the rectifier arrangement 7 and the voltage converter device 9 must therefore keep the intermediate voltage U _Z constant and absorb the excess current offered by the current source. For this purpose, the control device 8 can be designed as a generally customary parallel controller or as a periodically short-circuiting two-point controller. In the case of a parallel regulator, the current is controlled by a regulating device through a load resistor arranged in parallel in front of the voltage converters on the output side in such a way that the intermediate voltage U _Z remains constant. Here, however, the excess power is used uselessly. Taking into account the fact that a current transformer (in the present case this is the transformer 6 with current impressed on the primary side) may be short-circuited on the secondary side, the control device 8 can advantageously be designed as a periodically short-circuiting two-point controller. The load circuit of the parallel regulator is then replaced by a low-loss, periodically closing switching element 82 (e.g. transistor, preferably a power field-effect transistor), the duty cycle of which is controlled by a control element 81 so that the intermediate voltage U _Z remains constant. The two-point controller 8 thus alternately loads or shorts the transformer 6 with the input resistance of the consumer. Compared to a parallel controller, this two-point controller offers two major advantages. On the one hand, the voltage drop U 1 arising on the primary winding 61 of the decoupling transformer 6 is essentially determined by the resistance of the consumer on the output side and not by additional losses caused by a high-performance parallel regulator. On the other hand, the voltage drop U 1 does not also increase with increasing signal current I _S , but remains constant or drops slightly - depending on the losses occurring in the transformer 6. These important property ensures constant conditions in the signal circuit 1 even with different currents (day / night switching). A measured voltage curve ${\text{U₁ = f (I}}_{\text{S}}\text{)}$

is shown in Fig. 6. The operating points at night current (N) and at day current (T) are designated by N and T, respectively.

In the application shown in FIGS. 1 and 5, the voltage converter device 9 is designed for an input voltage U _E of 14 to 25 V, so that constant output voltages can be provided even with a flashing signal term and consequently intermittent signal current I _S. The prerequisite for this is that the storage capacitors 12 have a sufficiently large capacitance. The transformer windings additionally shown in FIGS. 1 and 5, each not provided with reference numerals, each with a subsequent rectifier bridge indicate that the power supply unit according to the invention is also suitable for extracting energy from a plurality of signal circuits.

In the exemplary embodiment shown in FIG. 5, the two-point controller 8 comprises an operational amplifier 81 which acts as a comparator and which switches the power field-effect transistor 82 via a driver circuit. The frequency and duration of the switch-on is determined by the position of the switching thresholds (comparator hysteresis), the time constant of the load and the current supply of the power source.

The power supply units according to FIGS. 1 and 5 are also protected against harmful overvoltages by voltage-limiting circuits. To limit the secondary AC voltage occurring at the transformer 6, two diodes are provided in parallel with the secondary winding 62 of the transformer 6. These Zener diodes 13 are connected in series at their anode-side connections.

Furthermore, a voltage limiter circuit 14 connected in parallel to the storage capacitors 12 and the voltage converter device 9 is provided. The voltage limiter circuit 14 comprises a transistor 141, the collector of which is connected via a resistor 142 to the “+” connection of the storage capacitors 12. The emitter of transistor 141 is connected to the "-" terminal of the storage capacitors 12. The transistor 141 is controlled via a zener diode 143 and the tap of a voltage divider 144 connected in series therewith.

The same transformer 6 as for the energy coupling can be used for the information coupling not explained here, if an additional coupling winding is applied for this. Another possibility for coupling out information is to insert a low-resistance measuring resistor (for example 1 ohm) into the “-” line of the rectifier bridge 7 in order to be able to tap a voltage drop that is proportional to the current.

Claims (12)

Power supply unit for data processing systems, in particular evaluation and coding circuits of punctiform train control devices, the unit comprising the following features: a) at least one signal circuit (1), in which at least one secondary winding (22) of a supply transformer (2) supplied with voltage by the AC circuit, a signal lamp (3) and a current monitor (5) are connected in series, b) to extract energy from the signal circuit (1), a transformer (6) operating according to the current transformer principle is connected with its primary winding (61) into the signal circuit (1), c) the transformer (6) is followed by a controllable rectifier arrangement (7) which rectifies the AC voltage (U₂) applied to the secondary winding (62) of the transformer (6) into an intermediate voltage (U _Z ) which is constant within predefinable limits, d) a voltage converter device (9) is connected with its inputs to the output connections of the rectifier arrangement (7) and with its outputs to the data processing system (10), e) a decoupling device (11) is connected to the output of the rectifier arrangement (7), f) an energy storage device (12) is arranged parallel to the rectifier arrangement (7) and to the voltage converter device (9).
Power supply unit according to claim 1, characterized in that
the rectifier arrangement (7) can be regulated by means of a regulating device (8), the regulating device (8) essentially comprising a regulating element (81) arranged parallel to the output connections of the rectifier arrangement (7) and a switching element (82) connected by the latter, through which the rectifier arrangement (7) can be short-circuited at its output connections. Power supply unit according to claim 2,
characterized in that
the control device is designed as a two-point controller (8). Power supply unit according to one of claims 1 to 3,
characterized in that
a power field-effect transistor (82) is provided as the switching element. Power supply unit according to claim 3 and 4,
characterized in that
the control element of the two-point controller (8) is an operational amplifier (81) which acts as a comparator and which switches the power field-effect transistor (82) via a driver circuit (83). Power supply unit according to claim 1,
characterized in that
the rectifier arrangement comprises a rectifier bridge (7) which is connected with its input connections to the connection terminals of the secondary winding (62) of the transformer (6). Power supply unit according to claim 1,
characterized in that
the decoupling device comprises at least one decoupling diode (11) which is arranged in series with at least one of the output connections of the rectifier arrangement (7). Power supply unit according to claim 1,
characterized in that
at least one storage capacitor (12) is provided as the energy storage device, which is parallel to the rectifier arrangement (7) and to the voltage converter device (9). Power supply unit according to claim 1,
characterized in that
at least two Zener diodes (13) connected in series and arranged parallel to the secondary winding (62) of the transformer (6) are provided for voltage limitation. Power supply unit according to claim 1,
characterized in that
between the energy storage device (12) and the voltage converter device (9) there is a voltage limiter circuit (14) connected in parallel to the latter. Power supply unit according to claim 10,
characterized in that
the voltage limiter circuit (14) comprises a transistor (141), the collector of which is connected via a resistor (142) to one input and the emitter of which is connected to the other input of the data processing system (10), and in that the transistor (141) is controlled via a Zener diode (143) and the tapping of a voltage divider (144) connected in series therewith. Power supply unit according to claim 1,
characterized in that
the secondary winding (22) of the feed transformer (2) is provided with taps to adapt the AC voltage applied to it to different position distances.

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