Electricity: electrical systems and devices – Control circuits for electromagnetic devices – Systems for magnetizing – demagnetizing – or controlling the...
Patent
1998-03-10
1999-08-03
Fleming, Fritz
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
Systems for magnetizing, demagnetizing, or controlling the...
361159, 361160, H02H 904, H01H 4722
Patent
active
059333120
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention is directed to a free-wheel circuit for eliminating a magnetic residual energy stored in a coil within a predetermined time.
BACKGROUND INFORMATION
German Patent No. 33 17 942 C2 describes a circuit arrangement for the protection of mechanical switchgear by an electronic switch. The mechanical switchgear assemblies are connected in series with ohmic inductive loads that are supplied with direct current. In this context, the electronic switch can be controlled by a capacitor that is charged from the load voltage. The electronic switch is connected in parallel to the load and becomes conductive when the switchgear is turned off. A non-linear resistor is connected in parallel to the electronic switch, and the parallel circuit is in turn connected in parallel to the load. The circuit arrangement operates in a manner similar to a free-wheeling diode connected in parallel to the load. As long as a control supply voltage source is connected to the load, the capacitor is charged and the electronic switch is conductive. As soon as the control voltage source is isolated from the load, the capacitor is discharged, resulting in the electronic switch becoming non-conductive. The current still flowing through the ohmic inductive load due to the stored magnetic energy is switched to the non-linear resistor by the electronic switch, resulting in a quick final decay of the residual energy stored in the inductance.
Such ohmic inductive loads include, for example, contactor coils supplied with direct current by a control supply voltage source, Depending on the size of the contactor and of the contactor coil used, decay times of 100 to 300 msec are obtained, which is still relatively slow for the requirements.
German Utility Model No. 94 09 760.7 describes a circuit arrangement for actuating a contactor. A free-wheeling branch, comprising a switching transistor and a free-wheeling diode connected in series thereto, is connected in parallel to the contactor coil. A free-wheeling controller controls the switching transistor as a function of the shape of the control voltage.
Furthermore, German Published Patent Application No. 43 21 127 describes a device for activating an electromagnetic load. This device comprises a series connection of the electromagnetic load with a first switching means, a free-wheeling circuit for the electromagnetic load, comprising a second switching means, and an actuator means for the switching means.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a free-wheeling circuit that will eliminate the magnetic energy stored in a coil, in general of an ohmic inductive load connected in parallel, within a shorter predetermined time period after it is disconnected from a control supply voltage source. The use of such a free-wheeling circuit for contactors allows a shorter, definite decay of the contactor. An advantage of this free-wheeling circuit consists of its self-controlled action resulting from the fact that, when switch-off surges occur in the coil, the free-wheeling transistor is reliably blocked and thus the current flow is switched to the non-linear resistor.
The present invention provides a free-wheel circuit that includes a series circuit that is parallel to the coil. The series circuit includes a first diode and a first switching transistor with which a non-linear resistor is connected in parallel. The free-wheel circuit of the present invention also includes a parallel circuit for driving the first switching transistor, the parallel circuit including a capacitor and a first ohmic resistor with which a second switching transistor is connected in parallel. According to the free-wheel circuit of the present invention, the residual magnetic energy of the coil is eliminated via the non-linear resistor.
BRIEF DESCRIPTION OF THE DRAWING
The drawing illustrates a free-wheeling circuit connected to a coil, in accordance with the present invention.
DETAILED DESCRIPTION
The drawing shows a free-wheeling circuit connected in p
REFERENCES:
patent: 5557494 (1996-09-01), Ishikawa et al.
patent: 5671115 (1997-09-01), Streich
Schuhbauer Thomas
Streich Bernhard
Fleming Fritz
Siemens Aktiengesellschaft
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