Electricity: electrical systems and devices – Control circuits for electromagnetic devices – For relays or solenoids
Patent
1998-10-23
2000-02-29
Fleming, Fritz
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
For relays or solenoids
361159, H01H 4704, H01H 4732
Patent
active
060317086
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an apparatus for controlling an inductive load, in particular the coil of an electromagnet, to which a recuperation diode is associated, this apparatus including an electronic chopper switch fitted in series with the coil and controlled by a pulse width modulator in accordance with a signal supplied by a device which measures the current of the coil.
Coil control apparatus of this type are well-known. The switch is controlled by the pulse width modulator and permits the coil to be initially powered with a high current, known as a signal current, to close the magnetic circuit of the electromagnet, then with a lower retaining current which is just sufficient to keep the magnetic circuit closed. Furthermore, it is known that the pulse width modulator is powered by a D.C. voltage circuit from a D.C. source or from the mains system.
In such an apparatus, rapid opening of the magnetic circuit of the electromagnet is sometimes sought; whereas in fact the free-wheeling current which continues to flow in the coil via the recuperation diode after the chopper transistor has been blocked slows down this opening. Therefore, using known methods, a second transistor known as rapid opening or rapid fall is connected in series or in parallel with the coil, and is solicited by an opening control circuit (for example, see the document DE 42 27 165).
The purpose of the invention is to permit the rapid opening transistor to be controlled over wide ranges of supply voltages at a voltage which floats with respect to the voltage at the coil terminals.
As claimed by the invention, the power supply circuit of the pulse width modulator is a transformer converter with two secondary windings, one of which is connected to the pulse width modulator and the other to the opening transistor gate by means of an opening switch that is solicited by the opening signal. The opening switch is preferably an optotransistor which leads to the discharging of the capacity of the rapid opening transistor gate when it is opened.
It is advantageously controlled by a circuit which includes a D.C. supply voltage comparator with at least one threshold, the output of the comparator being connected to a signal/retaining timer element and an opening timer device via a logic element fitted with a low level start-stop signal input.
The following description of a non-restrictive embodiment of the invention with regard to the appended Figures will explain how the invention may be put in practice.
FIG. 1 shows diagrammatically a control apparatus according to the invention for a contactor coil.
FIG. 2 shows an example of the embodiment of the opening transistor control of the apparatus shown in FIG. 1.
The apparatus shown is intended to control an electromagnetic contactor coil B or, possibly, the coils of two interdependent contactors associated in a change-over connection. It includes a chopper transistor T1 fitted in series with the coil, between the latter and a low potential point, for example 0 Volt, and a rapid opening transistor T2, also fitted in series with the coil, between the latter and a high potential line V+. A recuperation diode D is fitted in parallel to the series connection of the coil B and the transistor T2. Transistors T1 and T2 should preferably be insulated gate transistors, this concerns MOS transistors, but insulated gate bipolar transistors, known as IGBT's, may also be used. In one variation, coil B is connected directly to the V+ line and the transistor T2 fitted in series with the coil, between the latter and the point where it is connected to the diode D. In another variation, the transistor T2 and the diode D are fitted in series and the coil B in parallel to T2 and D.
The T1 chopper transistor is connected to the output of a pulse modulator circuit 11, which is part of a control circuit 10. A sensor 12 of the current flowing in the coil B is connected to the circuit 11 via a peak current detector 13. The elements which compose or are associated to the circuit 11 are typical and will not be described in fu
REFERENCES:
patent: 4947283 (1990-08-01), Kono
patent: 4949215 (1990-08-01), Studtmann et al.
patent: 5953198 (1999-09-01), Murata et al.
Fleming Fritz
Schneider Electric SA
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