Electrical transmission or interconnection systems – Switching systems – With operation facilitating feature
Patent
1999-06-11
2000-10-24
Jackson, Stephen W.
Electrical transmission or interconnection systems
Switching systems
With operation facilitating feature
361170, H01H 4712
Patent
active
061371939
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the field of relay control circuits employed for driving and controlling relays using microcomputers.
BACKGROUND OF THE INVENTION
One known technology for controlling relays and releasing welded contacts autonomously using a microcomputer is configured as shown in FIG. 6. More specifically, reference numeral 21 is a microcomputer, reference numeral 21a is a +DC power supply VDD, and reference numeral 21b is a power supply VSS on a common line with the load power supply. A relay 22 is connected to a relay control output 21c of the microcomputer 21 through a driver transistor 23. A contact 24a of the relay 22 is connected to a power supply 26 through a load 25, and another contact 24b is connected to an input 21d of the microcomputer 21 to detect welding of the contact 24a.
Control operations when the contact is welded in the above configuration is briefly described below.
When the relay control output 21c of the microcomputer 21 switches from ON to OFF, the coil voltage of the relay 22 turns OFF, and the load 25 also turns OFF. At this point, if the relay 24a is welded, the contact 24a remains turned ON and the recovery signal from the contact 24b for detecting welded contacts will not return to the input 21d of the microcomputer 21, thus generating the message that welding has occurred. This switches the control signal from the relay control output 21c of the microcomputer 21 to the welded contact release mode, in which a short pulse signal is applied to the coil of the relay 22 to release the welded contacts. If the contacts separate immediately, the welding releasing mode returns to the normal control mode. If not, the welding releasing operation is repeated until the contact is released.
With the above conventional configuration, however, a rise time is typically required by the relay driving power supply before a subsequent pulse can be applied to release the welded contacts. This causes a lack of continuity in the release pulse, decreasing its effectiveness.
Moreover, if an instantaneous power failure occurs during normal operation of the relay and the driving power supply of the relay is regained without reaching a sufficient sensory voltage level, the relay contacts may remain turned off, or contact pressure may become insufficient. In the worst case, the contact may generate heat, resulting in degradation of the reliability of the entire piece of equipment.
SUMMARY OF THE INVENTION
A relay control circuit controls the load at a contact of the relay. The relay control circuit comprises a microcomputer for controlling the relay, a welded-contact detector for detecting welded contacts in the relay and subsequently inputting a signal to the microcomputer, and first and second drivers for switching the relay control signal of the microcomputer, in response to the signal from the contact welding detector, to a short pulse signal if the contact is welded. The first and second drivers are employed to drive the relay in parallel.
Using this configuration, if welding of the contact occurs, an bombardment pulse effective in releasing the contact can be applied by driving the relay in parallel, thus enabling rapid release of the welded contacts. When a recovery problem of the contact occurs due to insufficient rise of driving power, the contact can be recovered by supplying the relay driving signal from another output port provided in parallel.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram showing a configuration of a control circuit of a relay in accordance with a preferred embodiment of the present invention.
FIG. 2 is a timing chart illustrating effect at occurrence of instantaneous power failure in accordance with the preferred embodiment.
FIG. 3 is a timing chart illustrating a welding release control pattern in accordance with the preferred embodiment.
FIG. 4 is a timing chart illustrating another welding release control in accordance with the preferred embodiment.
FIG. 5(a) is an enlarged view of the relay in accordance wi
REFERENCES:
patent: 4914315 (1990-04-01), Nickolai
patent: 5777301 (1998-07-01), Kim
Japanese Search Report corresponding to application No. PCT/JP98/03995 dated Dec. 15, 1998.
Copy/Form PCT/ISA/210.
Kikuoka Mitsuhiko
Shibata Satoru
DeBeradinis Robert L.
Jackson Stephen W.
Matsushita Electric - Industrial Co., Ltd.
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