DE2447199A1 - CIRCUIT ARRANGEMENT FOR CONTROLLING A RELAY - Google Patents

Description

115/74 He / SL

BBC Aktiengesellschaft Brown, Boveri & Cie, _, _ Baden (Switzerland)

Circuit arrangement for controlling a relay

The invention relates to a circuit arrangement for controlling a relay with a control circuit of with respect to the relay response voltage greater control voltage, with a current limiting device in the excitation circuit of the relay with an upper current limit value measured above the relay pick-up current, but below the load limit of the relay is arranged.

Circuit arrangements of this type are, for example, from the book "100 typical circuits with semiconductor components" by Pa. Intermetall 1967 p. 6 ¹ J and 65, known.

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For all electromagnets that do work by attracting an armature, e.g. in contactors, magnetic couplings and solenoids of all kinds happens, the amount Pick-up excitation a multiple of the holding excitation. It is therefore useful to pass the current through the coil of the magnet after Tightening to decrease. The power loss and thus the coil dimensions, pick-up and drop-out delays then remain small.

If such magnets are fed with alternating current, a relatively large current initially flows when the iron path is open. After the armature has picked up, the current falls to about 10-20? his Initial value. Such a reduction in current does not occur automatically with magnets that are operated with direct voltage one, but must be achieved by additional switching measures.

A common feature of the known circuit arrangements is a resistor connected in series with the magnetic coil, the is bridged by an electronic switch, e.g. a transistor, while the magnet is on.

Circuit arrangements of this type, however, are twofold fraught with disadvantages. The series resistor brings

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On the one hand, with it power losses that are applied by the control circuit Need to become. On the other hand, it must be dimensioned in such a way that the current required for holding excitation flows and the load limit of the solenoid is not exceeded in the hold state. Leave that way only comparatively small supply voltage fluctuations of - 20/5 are balanced out.

It is the object of the invention to provide a circuit arrangement create, which does not have the disadvantages of the known and which allows significant voltage fluctuations in the control circuit of the relay without affecting the operational safety of the relay.

This object is achieved according to the invention in a circuit arrangement for controlling a relay of the type mentioned at the beginning solved in that the current limiting device is a control device that can be switched over as a function of the excitation current with two switching states, the first switching state of which is dependent on the exceeding of an excitation current value above the relay pull-in current and the second of which If the excitation current value is lower in comparison, it results in a coupled to the control device Switching device is provided, the from the control circuit

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current drawn in the first switching state of the control device in relation to that in the second switching state of the control device taken lowers, and that the excitation circuit of the relay at least in the first switching state of the control device is closed via an additional cross-flow branch.

Further details of the invention emerge from the following Embodiment explained with reference to the drawing.

The excitation circuit of the relay consists of the series connection of an electronic switch S, the solenoid L of the relay and a current measuring element, e.g. a resistor R .. Between the connection line from switch S to coil L and ground is a freewheeling diode D. The electronic switch S is e.g. one of the transistors 1, 2 and the resistors 3, 4 existing Darlington circuit, the control terminal of which forms the base of transistor 2. The transistor 5 forms together with the base divider resistors 6 and 7, the emitter resistor 8, a current source Q, the between said Control connection of the electronic switch S and ground is switched. The base of the transistor 5 is via a further transistor 9 and its emitter resistor 10 connected to ground voltage divider consisting of resistors 11 and 12,

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whose tap is connected to the base of the transistor 9. These components 9,10,11,12 form an amplifier circuit whose output signal (collector voltage of transistor 9) is determined by the current flowing through the current measuring resistor R. Due to the connection of the two emitters of the transistors 5 and 9 by means of a diode 13 and a resistor I ¹ I connected in series with it, the circuit arrangement consisting of the current source Q and the aforementioned amplifier assumes bistable characteristics, such that when a 'certain Current value through the current measuring resistor R. the transistor 5 is blocked and thus the current source Q is switched off. Current source Q and amplifier together with the feedback form a current trigger T. A stabilization circuit consisting of a Zener diode 15 and a resistor 16 make the current trigger T largely independent of fluctuations in the control voltage U.

The mode of operation of the circuit arrangement described is evident from the following:

If the control voltage U is switched on, overflows

the current source Q immediately generates a current that switches the electronic switch S through. The excitation current flowing through the magnetic coil L increases (due to the self-inductance '. Der

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Coil exponentially. If this current falls below a certain Value i, the current trigger switches via the

nid. x

Current source Q the electronic switch S off. However, this does not prevent the flow of current in the solenoid L, because the energy stored in it via a cross-current branch, the freewheeling diode D, in the form of a flowing in the same direction Current continues to flow and is used in the solenoid. If this falls below this via diode D, coil L and Current measuring resistor R. flowing current a certain lower limit value i. , so the current trigger responds again, which in turn switches on the current source Q. The process described is then repeated.

If i are below the load limit of the relay and i. above the relay holding current, the excitation current of the relay oscillates continuously between these two values, however, the relay remains energized.

The mentioned limit values i. and i can be divided into simpler

mm max

Set the way by appropriately dimensioning the current trigger, whereby the characteristics of the relay are included in the dimensioning.

This should be illustrated with an example:

A 2 ^ volt contactor of certain design requires a pick-up current of i - tOO mA. The holding current is approx. 20% of this

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Value, so i. 80 mA.
mm

The current measuring resistor R. should be made as small as possible, since it is always in the relay circuit. One assumes from that to turn on the transistor 9 of the current trigger T. a voltage U- = 1 volt at the input of the current trigger, i.e. the voltage drop across R. is required, R. is calculated as follows

^U Tein

R ₁ = _τ = 2.5-0-

Max

Each trigger circuit has hysteresis behavior; the parameter for this the so-called hysteresis voltage U "is. She is de-

defined as the voltage difference between the switchover points with increasing and decreasing input voltage (cf. the aforementioned book "100 typical semiconductor circuits", p. 3D · The hysteresis voltage is determined by the circuit parameters certainly.

In the case of trigger circuits with a simple structure such as those in the exemplary embodiment these are between 1 volt and 0.1 volt.

U "can be influenced by the series resistor 12, among other things

(see also p.31> para. 3).

In the above example, the voltage U _{1 was} -,. _,

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When the excitation current increases, the current trigger "switches" accordingly at i, i.e. the constant current source Q is switched off. If you measure the trigger so that IL. = 0.8 volts attached

carries, "the Triffer switches on when the excitation current falls

^U Tans ^{= U} Tein " ^U H

^U Tans ^{= 1} HiIn * ^R i

^U Tans = °> ^{2 volts}

i.e. with a voltage drop at R. = 0.2 V, the current source becomes Q switched on again ..

The above explanations show that the hysteresis current of the trigger is always smaller than the hysteresis current of the Must be a relay.

The power requirement of the proposed circuit remains smaller compared to known arrangements, since only in each case closed electronic switch S energy is taken from the control circuit. This also makes the thermal Load on the electronic switch less. Another decisive advantage is that there are large fluctuations the control voltage U has a small influence on operational safety exercise more of the relay. The power requirement is also

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almost constant depending on the size of the control voltage U.

The higher this control voltage, the shorter the "charging times" for the magnetic coil, while the "discharging times ^{11 of} the magnetic coil remain constant and only depend on their characteristics (internal resistance, self-inductance, etc.) and the resistance of the current measuring resistor R. and the Disengage the freewheeling diode D.

Practical implementations of the circuit arrangement according to the invention with a 16-pole contactor type P 16, pick-up excitation current 300-400 mA, holding current approx. 50-80 mA, operating voltage 24 volts resulted in a working range for the control voltage ü of less than 30 volts up to 300 volts.

■ 6Q98-13 / 060J

Claims (9)

IO - 115/74 claims 1. I circuit arrangement for controlling a relay with a control _{circuit of greater control voltage with respect to the relay response voltage}} wherein a current limiting device with a current limit value measured above the relay pick-up current but below the load limit of the relay is arranged in the exciter circuit of the relay, characterized in that the current limiting device (T, R., S) has a control device (T) which can be switched over as a function of the excitation current and has two switching states, the first switching state of which is above the relay pick-up current depending on whether an excitation current value is exceeded and the second of which is lower when a comparatively lower one Excitation current value sets that a switching device (S) coupled to the control device (T) is provided, which entails the current drawn from the control circuit in the first switching state of the control device (T) in relation to the in the second switching state of the control device (T) assumed decreases, and that the excitation circuit of the relay (L) is closed at least in the first switching state of the control device via an additional cross-current branch (D). 13 / - 11 - 115/74 D 2. Circuit arrangement according to claim 1, characterized in that that the cross-flow branch is closed by a converter (D). 3. Circuit arrangement according to claim 1 or 2, characterized in that that the control device (T) is arranged as a function of one in the excitation circuit of the relay (L) Current measuring element (R.) is controlled. k. Circuit arrangement according to claim 1, 2 or 3> characterized in that the control device (T) has hysteresis behavior such that the transition from the first to the second switching state takes place with a higher excitation current than the transition from the second to the first switching state. 5. Circuit arrangement according to claim 4, characterized in that the hysteresis control range of the control device (T) an area of the relay current that covers the relay pick-up current assigned. 6. Circuit arrangement according to claims 4 or 5> characterized in that the hysteresis control area of the control device (T) is at most the same as the hysteresis current of the relay (L). 6098 1 3/0608 - 12 - 115/74 D 7. Circuit arrangement according to one or more of claims 1 to 6, characterized in that the control device (T) is designed such that, in the first switching state, the switching device (S) controls the relay (L) from the control circuit separates'. 8. Circuit arrangement according to one or more of claims 1 to 7, characterized in that the control device (T) consists essentially of a trigger circuit with a current output. 9. Circuit arrangement according to claim 8, characterized in that the hysteresis of the trigger circuit (T) is adjustable. BBC Public Company Brown, Boveri & Cie. 6098 1 3/0608