DE2760222C2 - Circuit arrangement for controlling a bistable relay - Google Patents

Description

with whose supply voltage is excited. This ensures the correct anchor position, namely normally closed contact, restored

With regard to the control of the bistable relay, this arrangement also behaves essentially like that from the "Relay Lexicon" or the DIi-PS 32 682 each known in such a way that the bistable relay is activated when the signal changes switches over at the control input For trouble-free operation, a permanent power supply is also required here the circuit arrangement must be ensured. The bistable relay is switched back in the event of failure the power supply is not guaranteed.

From DE-AS 26 24 913 there is also a circuit arrangement for controlling bistable relays known, which make them behave like monostable relays, i.e. automatically if the excitation voltage fails switch back to the starting position. This is achieved by having between the connection point of the excitation coil and capacitor on the one hand and which is connected upstream and that to the base electrode of the first Flip-flop transistor, a reference voltage is applied, so that the flip-flop only then becomes conductive when the excitation voltage exceeds the level of the reference voltage

These measures ensure that a relay can be controlled not only in black-and-white operation, that is to say with square-wave signals, but also with signals of finite edge steepness. The trigger stage suddenly becomes conductive when the reference voltage is reached, with the relay responding. The reference voltage can be specified in a simple manner by means of diode segments or the threshold voltage of Zener diodes. The possibility of setting their value in a larger range is particularly advantageous when using relays. In addition, the response and dropout voltage can be set more precisely than with conventional relays.
Further embodiments of the invention

The control electrode of the semiconductor switch, on the other hand, a circuit arrangement are defined in the subclaims

ne from the excitation voltage fed evaluation circuit is switched on, which the semiconductor switch at The presence of the excitation voltage blocks and controls conductively when it is no longer present. To prevent accidental When discharging the capacitor, a diode is also switched into the current path. A series resistor in the same path serves both as a short-circuit protection for the semiconductor switch as well as for appropriate dimensioning to achieve a deficit specified.

The invention is described in more detail below with reference to the figures. For a better understanding it is included initially in Fig. 1 and Fig. 2 on arrangements according to the parent application P 27 47 607.9-34. F i g. 3 shows an embodiment of the invention with fixed pull-in and drop-out voltages for the used relays.

In the case of the in FIG. 1 arrangement shown is a rened voltage drop, whereby relays with economical 30 ohmic resistance R 1 to the connections of the Errelich producible low-voltage winding to higher voltage U connected in parallel and with one of its voltages, z. B. the mains voltage are to be operated.
In contrast, however, the evaluation circuit required to achieve the monostable switching behavior of the relay leads to a relatively high outlay on components
len.

From DE-AS 12 79 777 a drop-out delay circuit for a bistable relay is known in which
a transistor stage in the parallel branch for series connection of relay and capacitor after the end of the 40
delay time causes the relay to switch back.
The particular advantage of this circuit is that
that after switching off the operating voltage without a
further power supply a longer drop-out delay is achieved. With this circuit the 45 is activated and is therefore blocked. After charging the semiconductor switch only for the expiry of the delay of the capacitor Ci only flows to it

Recharge required current as well as a current caused by the base resistance R 1. If the switch 5 is now opened or the excitation voltage üabge circuit arrangement of the type mentioned switches 50, the diode D 1 blocks, the emitter will be formed so that the electrode of the transistor Ti is positive when the excitation voltage is removed

Base electrode. The transistor Π is hereby controlled so that the capacitor C 1 can discharge through the excitation coil RIs of the relay. Through this

Connections connected to the diode D 1 serving as a resistance element, which is switched in the forward direction to the excitation voltage U. As a semiconductor switch, a transistor Ti is connected with its base electrode to the junction of diode D 1 and ohmic resistor R 1 and connected on the output side to the non-interconnected terminals of diode D 1 and ohmic resistor R 1

The excitation voltage is applied by closing the switch S , the relay RIs being excited by the charging current of the capacitor Cl. The transistor Ti is requested on the input side at the level of the threshold voltage of the diode Di in the reverse direction.

Time blocked This means increased power consumption while the operating voltage is applied. The invention is now based on the object of a

desired automatic switching back of the bistable relay can be implemented with less expenditure on components is than in the known arrangement and that except

a defined pull-in voltage for the 55 used switches the bistable relay to its starting position

th relay is set.

According to the invention, this object is achieved in that the semiconductor switch is connected with its control input to the excitation voltage, back from this. In the case of monostable switching behavior, the present arrangement draws from the excitation voltage source, apart from the losses in the base resistance R 1 and capacitor Cl, only to charge the capacitor

blocks and on the output side of the series circuit of spooler C 1 energy. The low cost of structural elements

Ie and capacitor are connected in parallel, with a resistor arrangement in series with this parallel connection lies in such a way that the semiconductor switch after the capacitor has been charged and switched off the excitation voltage can be controlled in a conductive manner by a voltage drop occurring across the resistor arrangement is. and that the resistor arrangement has a trigger stage made up of complementary transistors ten also enables an economical and space-saving construction. The whole is preferred Arrangement housed in the housing provided for the relay.

Instead of the diode D 1, an ohmic resistor can in principle also be used as the resistance element. However, the diode Di provides a guarantee against a slow discharge of the capacitor Cl

they limit the voltage drop at the input circuit of the transistor Ti during the charging of the capacitor Cl to its threshold voltage and thus to a harmless level. To charge the capacitor CX , the excitation voltage LJ is also only reduced by the threshold voltage of the diode D 1. If the polarity of the excitation voltage L / is incorrect, the diode D 2 serves as protection for the transistor Π.

In the case of the in FIG. 2, the diode D 1 is preceded by a Zener diode ZD 1 in the forward direction to the excitation voltage U. The diode D 1 is bridged by an ohmic resistor Rl and a flip-flop consisting of two transistors 7-2, 7 "3 of opposite conductivity type is provided as a semiconductor switch. The collector electrode of one transistor is connected to the base electrode of the other transistor In this embodiment, a defined value is set for the drop-out voltage of the relay. The drop-out voltage results from the difference between the excitation voltage U and the Zener voltage Uzo \ - If the excitation voltage U is switched on via the switch Se, the charging current of the capacitor C 1 flows through the The Zener diode ZD 1, the diode D 1 and the excitation voltage divider are connected in parallel to the connections of the excitation voltage (U) . One of the divider resistors (R 3) is connected to the anode of the diode D 1 connected to the excitation voltage U. The semiconductor switch is connected to its control electrode to the center tap of the voltage divider R 3, R 4 and connected on the output side to the connections of the resistor element facing away from the one dividing resistor R 3 and the other dividing resistor /? 4. In this case, the drop-out voltage of the relay is determined by the ratio of the divider resistances R 3, RA . The switch, a flip-flop made up of complementary transistors T2, T3 , in which the collector electrode of one flip-flop transistor is connected to the base electrode of the other flip-flop transistor and in which the emitter electrode of one transistor Tl is connected to the cathode of diode D 1 and the emitter electrode of the other Transistor Γ3 is connected to the common base of the circuit arrangement, after the capacitor C 1 has been charged in the manner already described, it becomes conductive when the excitation voltage U has dropped to the value of the desired drop-out voltage. For the defined definition of the switching point and to prevent the unintentional

Ie RIs. This energizes the relay and switches over. 25 visible switching through of the flip-flop when it occurs

At the diodes ZD 1 and D 1, voltage drops in the amount of their threshold voltages occur again. The pnp transistor 7-2 is blocked as a result, as is the case with the arrangement of FIG. 1 has already been described. Accordingly, the npn transistor 7-3 is also blocked.

After charging the capacitor Cl, a flow of current of the capacitor C 1 and to a current through the resistor R 1. This leakage current in turn is limited essentially to the recharging can be maintained, however, in this case much smaller than in the case of F i g. 1, because the base resistance R 1 can be made larger as a result of the higher overall gain of the trigger stage formed from the transistors T2, T3. The resistance R 2 creates the same potential at the anode and cathode of the diode D 1, which ensures that the trigger stage 7 "2, T3 is blocked.

If the excitation voltage U now drops slightly, the potential present at the cathode of the Zener diode ZD 1 is essentially retained because the Zener diode ZD 1 is stressed in the reverse direction. Only when the excitation voltage U has dropped so far that the voltage drop across the Zener diode ZD 1 causes the zener of voltage peaks, another npn transistor Γ4 is connected upstream of the flip-flop transistor, in such a way that its collector electrode with the base electrode of the flip-flop transistor 73, its base electrode with the center tap of the Voltage divider Λ 3, RA and its emitter electrode is connected to the common base of the circuit arrangement.

In order to obtain a defined pull-in voltage, it is provided that the diode D 1 serving as a resistance element is preceded by a further flip-flop made up of complementary transistors Γ5, 7 "6 and that a reference voltage is applied to the base electrode of the first flip-flop transistor Γ6 such that the flip-flop only becomes conductive when the excitation voltage U exceeds the level of the reference voltage. The reference voltage specifies the desired pull-in voltage. As soon as the excitation voltage U exceeds the reference voltage, the flip-flop 7 * 5, T6 becomes conductive. The charging current of the capacitor CT can now flow through the diode Di and the exciting coil RIs, so that the relay operates. falls below the excitation voltage, the reference voltage U, so disables the flip-flop 7 "5, T 6 is to achieve the reference voltage between the base electrode

zero old

voltage Uzo ι reached, this becomes conductive. Through the 50 of the first transistor T6 and the common ground

sepoter.tia! of the circuit arrangement, the series connection of an ohmic resistor Rl and a Zener diode ZD 2 polarized in the reverse direction to the excitation voltage are switched on

In order to ensure that the residual currents of the transistors T5, T6 are kept small and an unintentional switching of the trigger stage is avoided, the base-emitter paths of the transistors T5, TS are bridged with ohmic resistors R 5, R 6 The emitter electrode of the transistor T6 is provided in order to prevent the trigger circuit 7 "5, 7" 6 from being switched through too early when the excitation voltage U is switched on.

A rectifier D 2 is switched on so that the circuit arrangement can also be operated with alternating voltage. In direct voltage operation, it serves as protection against polarity reversal. In addition, there is a capacitor C4 in the input circuit of the semiconductor switch TA, T3, T2

D \ and resistance R 2 occurring voltage drop is the transistor T2, its base current can now flow through the Zener diode ZD i and the ohmic resistor R i , and thus the complementary transistor Γ3 is turned on. The capacitor Ci is now discharged via the excitation coil RIs, as a result of which the relay switches back to its starting position

In addition to the advantage of one compared to the circuit according to FIG. 1 reduced leakage current results in the circuit according to FIG. 2 through the implementation of a defined drop-out voltage that fluctuations in the excitation voltage U from its maximum value up to the drop-out voltage can be permitted without the relay being unintentionally switched back.

Like F i g. 3 shows, a defined drop-out voltage can also be achieved in that a voltage voltage consisting of two ohmic resistors (R 3, RA)

arranged, the capacity of which is chosen so large that
the resulting discharge time constant is greater than that
The duration of the voltage drops caused by the rectification.

1 sheet of drawings

10

20th

25th

30th

35

40 ■% '

45

50

55

60

65

Claims (4)

Patent claims: 1.Circuit arrangement for controlling a bistable relay, the excitation coil of which is in series with a capacitor, in which the series connection of coil and capacitor for excitation of the relay and simultaneous charging of the capacitor is applied to excitation voltage and, in the absence of excitation voltage, by one with its output circuit to it Semiconductor switch connected in parallel can be short-circuited, whereby the relay switches back to its starting position, characterized in that the semiconductor switch (T 1; Γ2, Γ3; T2, TZ, T4) is connected with its control input to the excitation voltage (U) , blocked in front of it and on the output side d ^ r series connection of coil (RIs) and capacitor (Ci) is connected in parallel, with a resistor arrangement (D 1; Dl, R 2) in series with this parallel connection, such that the semiconductor switch (TV, T2, T3; Tl, 73, T 4) after the capacitor CCl) has been charged and the excitation voltage (U) has been switched off by an at de r resistor arrangement (DV, D I ₁ R 2) occurring voltage drop is conductive controllable and that the resistor arrangement (Di; Di, R 2) is preceded by a flip-flop made up of complementary transistors (T5, T6) and that a reference voltage is applied to the base electrode of the first flip-flop transistor (T6), such that the flip-flop only becomes conductive when the excitation voltage is as high as the Reference voltage exceeds. 2. Circuit arrangement according to claim 1, characterized in that the collector electrode of the first Kippstufent.-ansistor (pnp) (T6) with the base electrode of the second flip-flop transistor (npn) (T5) and the collector electrode of the second flip-flop transistor (TS) with the base electrode of the first flip-flop transistor (TS) is connected that the base-emitter paths of both transistors (T5, T6) are each bridged with an ohmic resistor (R 5, R 6) and that between the emitter electrode of the first transistor (T6 ) and the base electrode of which is a capacitor (C 2) . 3. Circuit arrangement according to claim 1 or 2, characterized in that in order to achieve the reference voltage between the base electrode of the first transistor (TS) and the common ground potential of the circuit arrangement, the series connection of an ohmic resistor (R 7) and a reverse-biased Zener diode ( ZD 2) is switched on (Fig. 3). 4. Circuit arrangement according to one of the preceding claims, characterized in that the excitation voltage (U) practice. ¹ a rectifier (D 2) is supplied and a capacitor (C 4) is switched on in the input circuit of the semiconductor switch and that the capacitance of the capacitor (C 4) is chosen so that the resulting discharge time constant is greater than the duration of the selected type of Rectification is caused by voltage dips. The invention relates to a circuit arrangement for controlling a bistable relay, its excitation coil with a capacitor in series, in which the series connection of coil and capacitor for excitation of the relay and simultaneous charging of the capacitor is applied to the excitation voltage and if there is no Excitation voltage through a semiconductor switch connected in parallel with its output circuit can be short-circuited, whereby the relay switches back to its starting position. A circuit arrangement for switching a bistable relay with the aid of a semiconductor switch is known, for example, from the book "Relais Lexikon" by H. Sauer, 1st edition 1975, page 12 lying transistor conducting, the relay responds and the capacitor is charged. If a positive control signal is applied to the input of a second transistor, the first transistor is blocked and a third transistor, lying parallel to the coil and capacitor, is conductive. This third transistor discharges the capacitor and the relay switches back. If the control signal jumps to the value Nu ¹ I ₁ then the second and the third transistor are blocked again, the first transistor is conductive, the capacitor is recharged, which causes the relay to switch. A circuit arrangement of this type is also known from DD-PS 32 682, two being connected in series and emitter-operated transistors that alternate depending on the control voltage Lead current, controlled by a driver transistor. The connecting line of the series-connected Transistors represents the output to which a capacitor is connected and via which one or more are connected controlling polarized relays are connected. Such circuit arrangements are useful for the operation of bistable relays if the polarity the excitation voltage remains unchanged. The relay persists in its charge after the capacitor has been charged Switch position, regardless of whether the excitation voltage is switched off or is still present. in the The case of the circuit arrangement known from the "Relay Lexicon" also prevents a series connection If there is no excitation voltage, the diode causes a gradual discharge of the capacitor. A downshift of the relay is only triggered here by the positive control pulse at the input of the second transistor. In the case of the circuit arrangement known from DD-PS 32 682, the relay is switched back caused by switching off the control signal from "1" to "0" at the input of the driver transistor. After this the control pulse or the control signal cannot be obtained from the excitation voltage if If this is switched off, there is a need for an external control signal source. Furthermore, from DE-OS 25 15 214 a circuit arrangement for controlling and monitoring the switching position of a bistable relay known in which a changeover contact of the relay is used. A wrong switch position occurs when the live Relay armature is connected to the normally open contact before or after the supply voltage is applied to a Control circuit is present while at the same time the supply voltage of a monitoring circuit is present is. In this case the control circuit is blocked and the monitoring circuit is conductive, so that the relay winding via the normally open contact and the monitoring circuit