Circuit for controlling current through relay coil

Abstract

The invention relates to a circuit for controlling a current through a relay coil, comprising an electronic switch for controlling the current through the relay coil and a comparator for controlling a control voltage applied to a control terminal of the electronic switch, a first voltage being applied to a first input terminal of the comparator, and a second voltage being applied to a second input terminal of the comparator. A second voltage is applied to the second input of the comparator, said second voltage being derived from the current through the relay coil, and the circuit is designed to reduce the current through the relay coil to a holding current after a switching process caused by a switching current through the relay coil.

Description

TECHNICAL FIELD

[0001] The present invention relates to a circuit for controlling the current through a relay coil. The invention particularly relates to a circuit for reducing the holding current. BACKGROUND

[0002] By varying the magnitude of the current through the relay coil, a magnetic field can be generated which either establishes contact between two electrical conductors or separates two mutually contacting electrical conductors from each other. SUMMARY

[0003] The circuit for controlling the current through a relay coil according to the invention comprises an electronic switch which controls the current through the relay coil, and a comparator which controls a control voltage applied to the control terminal of the electronic switch, wherein a first voltage is applied to a first input terminal of the comparator and a second voltage derived from the current through the relay coil is applied to a second input terminal of the comparator. The circuit according to the invention is further designed to reduce the current through the relay coil to a holding current after a switching process caused by the switching current through the relay coil.

[0004] Herein, the term "circuit" used in the description and claims is to be understood as a functional structure of a combination of electrical and / or electronic elements, in particular. Furthermore, the term "comparator" used in the description and claims is to be understood as an electronic element which detects two input voltages and outputs an output voltage which changes in level when the sign of the difference between the input voltages changes. For example, the output voltage can be U A1 when the first input voltage is greater than the second input voltage, and U A2 when the second input voltage is greater than the first input voltage.

[0005] Furthermore, the term "relay coil" used in the description and claims is to be understood as a coil of a relay which is designed to generate a magnetic field which moves a mechanical component from a first position, for example a rest position in which no current flows through the coil, to a second position, for example a holding position, in order to close or open a current loop. Herein, the holding position can be a position in which the component is pressed against a stop by the magnetic field (against a return force). The magnitude of the return force can be determined such that the component is driven back into the rest position by the return force when the relay coil is not supplied with current, thereby opening the current loop, for example.

[0006] In this context, the term "holding current" as used in the description and claims is to be understood in particular as a current sufficient to generate a magnetic field which holds the component in the holding position (against the return force). Furthermore, the term "switching current" as used in the description and claims is to be understood in particular as a current sufficient to generate a magnetic field which forces the component to move from the rest position to the holding position (against the return force and the static friction in the rest position), whereby the "switching current" is greater in value than the "holding current".

[0007] The comparator can be part of a switching regulator designed to use the relay coil (instead of a separate energy storage choke) as a magnetic energy store (jointly). With such a switching regulator a constant current source can be realized which allows to operate the relay coil with constant current, whereby the magnetic field and the holding force are independent of the operating temperature and the operating voltage of the circuit. The current target value can be set for example by a reference voltage applied to the comparator, wherein the reference voltage is influenced by an RC circuit such that the current is higher at switch-on to attract the relay and subsequently drops to the holding current.

[0008] The circuit can thus comprise a voltage source designed to output a constant voltage for starting the switching process, and an electrical element structure arranged between the voltage source and the first input of the comparator, which electrical element structure derives a first voltage from the constant voltage, wherein the structure is such that the first voltage drops after a certain time period to a level which results in the holding current. In particular, the electrical element structure can comprise an RC circuit.

[0009] The first input of the comparator can be connected to the voltage source by means of a voltage divider. The circuit can further comprise a switch which bridges a resistor of the voltage divider when the switch is closed. The circuit can further comprise a capacitor, wherein the voltage divider comprises a resistor in parallel to the capacitor.

[0010] The circuit according to the application can be comprised in an apparatus together with a relay comprising a relay coil.

[0011] The method according to the application comprises generating a current through the relay coil by outputting a constant voltage by means of a voltage source to cause a switching process, and reducing the current through the relay coil to a holding current (I H ) after the switching process has been caused.

[0012] Furthermore, it goes without saying that the features described in connection with the circuit can also be features of the method and vice versa. BRIEF DESCRIPTION OF DRAWINGS

[0013] In the following, the application is explained in detail by means of embodiments, with reference to the drawings, in which

[0014] Figure 1 a schematic diagram of a circuit according to the application is shown;

[0015] Figure 1a the variation of the current through the relay coil is shown, which is controlled by the circuit shown in Figure 1 ;

[0016] Figure 2 a first embodiment of the circuit shown in Figure 1 ;

[0017] Figure 3 a second embodiment of the circuit shown in Figure 1 ; and

[0018] Figure 4 a flow chart of a method according to the application is shown.

[0019] Herein, identical or functionally similar elements in the figures are denoted by identical reference numerals. DETAILED DESCRIPTION

[0020] Figure 1 A schematic diagram of a circuit 10 according to the application is shown. The circuit 10 comprises a relay coil 12 and an electronic switch 14, which controls the current I through the relay coil 12. The output voltage of a comparator 16 is applied to the control terminal of the electronic switch 14. A voltage Ul is applied to the first input 16-1 of the comparator, which voltage is derived from the (constant) output voltage U of a voltage source 18, e.g. a linear voltage regulator, by means of an electrical component structure 20. k The voltage source 18 can also provide the operating voltage for the switching regulator in addition to the reference. The voltage source 18 can also be a switched voltage regulator.

[0021] A second voltage U2 is applied to the second input 16-2 of the comparator 16, which is wired as a Schmitt trigger, and which is derived from the current I through the electronic switch 14 and the relay coil 12. If the current I through the electronic switch 14 and the relay coil 12 drops, then the voltage U2 drops. If the voltage U2 drops below the voltage Ul, then the output voltage of the comparator 16 inverts, and the electronic switch 14 is turned on, so that the current I rises again. If the value of the voltage U2 exceeds the value of the voltage Ul, then the electronic switch 14 is turned off, and the current I drops again. Thus, a triangular wave current I through the relay coil 12 is generated, which has an average value equal to the set target value. Instead of the switching regulator shown, an integrated module can also be used, e.g. a constant current driver for light emitting diodes.

[0022] As shown in Figure 1a , the electrical component structure 20 ensures that the (constant) voltage U is output when the voltage source 18 is started up.k At this time, the reference voltage U1 temporarily increases. This causes a (larger) initial switching current I to flow through the relay coil 12. S After a specific duration following the end of the switching process (e.g., after a duration after which the relay has been engaged), the switching current decreases to the holding current I. H By reducing the current I flowing through relay coil 12 to the holding current I... H This can reduce the energy consumption of circuit 10.

[0023] Figure 2 Show Figure 1 One possible implementation of the circuit 10 shown is as follows. The electrical component structure 20 includes a voltage divider 22 that connects the first input terminal 16-1 of comparator 16 to the voltage source 18. If switch 24 is closed, the resistor 26 of the voltage divider 22 is bridged, causing the voltage U1 applied to the first input terminal 16-1 of comparator 16 to decrease. The timing of the switch 24 closing can be determined by the parameter design of capacitor 28 and resistor 30 such that the voltage U1 decreases from the voltage source 18. k The duration of the output to the closing of switch 24 is long enough to end the switching process.

[0024] Figure 3 Show Figure 1 Another possible implementation of the circuit 10 shown. In this implementation, the electrical component structure 20 also includes a voltage divider 22, through which the first input terminal 16-1 of the comparator 16 is connected to the voltage source 18. However, here the capacitor 28 is connected in parallel with the resistor 26 of the voltage divider 22, so that when the capacitor 28 charges, the voltage U1 applied to the first input terminal 16-1 of the comparator 16 decreases. Here, the timing or rate of voltage U1 decrease can be determined by the parameter design of the capacitor 28 and the resistor 26 such that the current I through the relay coil 12 decreases to the holding current I. H The switching process was terminated earlier.

[0025] Figure 4 A flowchart of the method according to the present invention is shown. The method begins at step 32, by outputting a constant voltage U from voltage source 18. k This generates a current I through the relay coil 12 to initiate a switching process. In step 34, after the switching process has been initiated, the method reduces the current I through the relay coil 12 to a holding current I. H And so it ends.

[0026] List of reference numerals

[0027] 10 Circuits

[0028] 12 relay coil

[0029] 14 switch

[0030] 16 comparator

[0031] 16-1 input terminal

[0032] 16-2 input terminal

[0033] 18 voltage source

[0034] 20 structure

[0035] 22 voltage divider

[0036] 24 switch

[0037] 26 resistor

[0038] 28 capacitor

[0039] 30 resistor

[0040] 32 step

[0041] 34 step

Claims

1. Circuit (10) for controlling the current (I) through a relay coil (12), comprising: - an electronic switch (14) which controls the current through the relay coil (12); and - a comparator (16) which controls a control voltage applied to a control input of the electronic switch (14); wherein a first voltage (Ul) is applied to a first input (16-1) of the comparator (16); wherein a second voltage (U2) derived from the current (I) through the relay coil (12) is applied to a second input (16-2) of the comparator; characterized in that 2. Circuit (10) for controlling the current (I) through a relay coil (12) according to claim 1, further comprising: - an electrical element structure (20) connected between the comparator (16) and the electronic switch (14). The circuit (10) is designed to reduce the current (I) through the relay coil (12) to a holding current (I H ) after a switching process caused by a switching current (I S ) through the relay coil (12).

3. Circuit (10) for controlling the current (I) through a relay coil (12) according to claim 2, a voltage source (18) designed to output a constant voltage (U k ) for starting the switching process; the electrical element structure (20) comprises an RC circuit. An electrical element structure (20) is arranged between the voltage source (18) and a first input (16-1) of the comparator (16), which electrical element structure derives a first voltage (Ul) from the constant voltage (U k ), wherein the electrical element structure (20) reduces the first voltage (Ul) after a certain period of time to a level which causes the holding current (I H ) to be drawn.

4. Circuit (10) for controlling the current (I) through a relay coil (12) according to one of claims 1 to 3, wherein, the first input (16-1) of the comparator (16) is connected to a voltage source (18) via a voltage divider (22).

5. Circuit (10) for controlling the current (I) through a relay coil (12) according to claim 4, further comprising: wherein - a switch (24) which, when closed, bridges a resistor (26) of the voltage divider (22).

6. Circuit (10) for controlling the current (I) through a relay coil (12) according to claim 4, further comprising: - a capacitor (28); wherein the voltage divider (22) comprises a resistor (26) in parallel to the capacitor (28).

7. Apparatus comprising a relay with a relay coil (12) and a circuit (10) for controlling the current (I) through the relay coil (12) according to one of claims 1 to 6.

8. Method for controlling the current (I) through a relay coil (12), comprising: - applying a first voltage (Ul) to a first input (16-1) of a comparator (16); and - applying a second voltage (U2) derived from the current (I) through the relay coil (12) to a second input (16-2) of the comparator. By outputting a constant voltage (U k ) from the voltage source (18), an electric current (I) is generated through the relay coil to cause a switching process; ​ After the switching process has been initiated, the current (I) through the relay coil (12) is reduced to a holding current (I H ).

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