Electricity: electrical systems and devices – Control circuits for electromagnetic devices – For relays or solenoids
Patent
1995-12-22
1997-09-23
Fleming, Fritz
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
For relays or solenoids
361154, H01H 4722
Patent
active
056711158
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a circuit arrangement for driving a contactor in which in the control circuit of the contactor, a controllable switching element, a measuring resistor and the contactor coil of the contactor are in series with a control voltage source and the switching element co-operates with a regulation device such that the contactor is supplied with a starting current of constant average value and the regulation device is connected to switchover means for selecting different starting currents, corresponding to the power classes of different contactors.
Contactors are remote control switches with an electromagnetic actuator. A distinction is made between a control circuit of the contactor with a contactor coil and a load circuit of the contactor to be switched with the connected loads. As soon as a sufficient starting current flows through the contactor coil, the contactor responds and turns on the loads connected in the load circuit. To maintain the contactor in this state, a holding current must flow through the contactor. After the holding current is switched off, the contactor drops out. The energy stored in the contactor coil is dissipated in a free-wheeling circuit.
In German Patent No. DE-OS 37 01 985, series electronic circuitry for a contactor coil is described. A fast power switch and a shunt resistor are arranged in series with the contactor coil which has a free-wheeling diode connected to it. The shunt and the power switch are connected to control electronic circuitry fed from a constant current source.
When the power switch is closed, there is a voltage drop across the shunt resistor which is proportional to the flow of current through the contactor coil. This voltage is compared in a first comparator with a reference voltage tapped off a voltage divider. At the output of this first comparator, a second comparator is connected which has at its positive input a further comparison voltage which drops across another divider tap of the voltage divider. This second comparator drives the fast power switch. The series electronic circuitry requires a relatively low nominal voltage as an operating voltage and can also be used in conjunction with different higher nominal voltages since in the regulation of the contactor coil current, the important matter is not the absolute magnitude of the threshold values present on the comparators but rather their ratio. The ratio of these threshold values is determined through the sizing of the voltage divider.
Accordingly, the series electronic circuitry can be used in conjunction with different operating voltages. In order to drive a contactor of another power class, series electronic circuitry with a differently sized voltage divider is required in each case.
From German Patent No. DE-OS 40 03 179, it is known to arrange a field-effect transistor in the control circuit of the contactor which switches the starting current of the contactor. In parallel to the contactor coil, a free-wheeling diode is provided as a free-wheeling branch.
From German Patent No. DE-OS 37 33 091, it is known to provide in the free-wheeling branch parallel to the contactor coil in addition to the free-wheeling diode a free-wheeling switch which is driven by a control stage based on a closing signal provided by a higher-ranking computing unit. A switch connected in series with the contactor coil is also driven by the same closing signal. The regulation of the free-wheeling branch and of the current flowing through the contactor coil are thus coupled. The dropout time of the contactor is regulated based on the current flowing through the contactor coil.
Moreover, it is known from German Patent No. DE-OS 37 33 091 to provide a measuring resistor in the control circuit of the contactor, the voltage drop across this measuring resistor being a measure for the control current flowing in the control circuit. This voltage drop is compared in a comparator with a value specified by a voltage divider. The voltage divider is set using a potentiometer re
REFERENCES:
patent: 4618908 (1986-10-01), Anttila
patent: 4949215 (1990-08-01), Studtmann et al.
patent: 5459631 (1995-10-01), Leone et al.
patent: 5490031 (1996-02-01), Braun et al.
patent: 5557494 (1996-09-01), Ishikawa et al.
Fleming Fritz
Siemens Aktiengesellschaft
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