Electricity: electrical systems and devices – Control circuits for electromagnetic devices – For relays or solenoids
Patent
1997-10-13
1999-12-07
Fleming, Fritz
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
For relays or solenoids
361154, H01H 4732
Patent
active
059993960
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a circuit for driving a contactor, where a controllable switching element, a measurement resistor and the contactor coil are connected in series to a control voltage source in the control circuit of the contactor, and a pickup current control circuit is provided to pick up the voltage on the measurement resistor.
A circuit of this type is disclosed in German Offenlegungsschrift No. 43 21 252. Control circuit 34 of a contactor as illustrated in FIG. 2 here comprises a rectifier block 7 of a control voltage source and a contactor coil 1, a switching element 2 and a measurement resistor 3 connected in series. A pickup current control circuit 24 that is in operative connection with switching element 2 via a logic element 8 is connected to measurement resistor 3; logic element 8 is connected to switching element 2 by a driver stage 26. In addition, a setpoint device 25 is connected to pickup current control circuit 24 to supply a reference voltage. Logic element 8 is also connected to a programmable control device 27 and a mechanical actuator 28. In addition, logic element 8 is also connected from a voltage shaping circuit 31 to a pulse width modulator 33 either directly or via a time control device 32.
Rectifier block 7 contains a first bidirectional rectifier 71 to which control circuit 34 is connected and a second bidirectional rectifier 72 that supplies a supply circuit for the voltage shaping circuit 31 and a free-wheeling control 30. Furthermore, this supply circuit also includes a power supply device 29 that supplies the operating voltage for all the consumers of the circuit that are not supplied directly from rectifier block 7.
A free-wheeling arm 4 is connected to contactor coil 1. A free-wheeling switching element 18 and a free-wheeling diode 17 are connected in series in this free-wheeling arm 4. Free-wheeling control 30 is connected to the control input of free-wheeling switching element 18. Free-wheeling control 30 is in signal connection with voltage shaping circuit 31.
The circuit works in such a way that a control current flows in control circuit 34 as soon as a corresponding control signal from a master control is switched to control circuit 34. Due to the fact that contactor coil 1 is under a current, the contactor picks up. The pickup current is then kept constant by the fact that a measurement voltage proportional to this pickup current is picked up at measurement resistor 3 and sent to pickup current control circuit 24 containing a comparator. The comparator compares the measurement voltage with a reference voltage of setpoint adjusting device 25. The switching threshold of the comparator can be changed by adjusting the reference voltage level. The selectable reference voltage corresponds to the respective pickup current. The holding current, which is smaller than the pickup current by a factor of 20 to 30, is achieved by means of the pulse width modulator, that is connected to logic element 8. ON time periods of switching element 2 of varying duration are achieved by pulse width modulation corresponding to the control voltage applied to the voltage divider at each instant, and in this way a relatively lower holding current is achieved.
The pulse width modulator requires a plurality of components, including a monoflop and an oscillator plus an RC element. From the standpoint of an inexpensive solution, it would be a great advantage to be able to do without the pulse width modulator.
Therefore, the object of this invention is to create a circuit of the above-mentioned type that will be inexpensive and will require only a few components.
This is achieved according to this invention by a circuit of the above-mentioned type where a series connection of an additional electronic switching element and an additional resistor is in parallel with the measurement resistor.
Advantageous embodiments of this invention are characterized in subclaims 2 through 4.
One embodiment of this invention is explained in greater detail below with reference to FIG. 1. The circuit illustrated he
REFERENCES:
patent: 3786314 (1974-01-01), Misch
patent: 3852646 (1974-12-01), Mason
patent: 4291358 (1981-09-01), Dettmann et al.
patent: 4620261 (1986-10-01), Thornton
patent: 5621603 (1997-04-01), Adamec et al.
Fleming Fritz
Siemens Aktiengesellschaft
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