Electrical transmission or interconnection systems – Switching systems – Condition responsive
Patent
1995-07-19
1996-11-12
Wysocki, Jonathan
Electrical transmission or interconnection systems
Switching systems
Condition responsive
307102, 307141, 361 18, 361 86, 361 93, 361187, 340507, 365226, H02H 300
Patent
active
055743200
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a fail safe load drive circuit which is able to forcibly interrupt a load current to a load at the time of a short circuit fault in a switch element of a switch circuit for switching the load current on and off.
BACKGROUND ART
A conventional load drive circuit which has heretofore been proposed (refer to U.S. Pat. No. 4,661,880 in the name of one of the applicants of the present invention) involves an electromagnetic relay contact, and a switch circuit using for example a semiconductor switch element, connected in series in a load feeder circuit. With this load drive circuit, power supply to the load is controlled by inputting a load drive signal to the switch circuit to switch the semiconductor switch element on and off, and if a conduction fault occurs in the semiconductor switch element, this is detected and the electromagnetic relay contacts switched off to forcibly interrupt the load current.
The structural theory of such a conventional load drive circuit is explained with reference to FIG. 9.
In FIG. 9, relay contacts 5A of an electromagnetic relay 5, and a switch circuit 4 using a semiconductor switch element such as an SSR (solid state relay), are connected in series in a load feeder circuit 3 wherein a load 2 is connected in series to a power source 1. The presence or absence of a load current I.sub.L in the load feeder circuit 3 is detected by a zero current detection sensor 7 through a current transformer 6. An output signal I.sub.P of the zero current detection sensor 7 and a load drive signal I.sub.N are input to an OR gate 8, and the contacts 5A of the electromagnetic relay 5 are driven open or closed depending on a logical sum output of the OR gate 8. The load drive signal I.sub.N is made a binary signal (logic value "1", "0") which does not err to logic value "1" at the time of a fault.
The zero current detection sensor 7, is one which gives an output signal I.sub.P of logic value "1" corresponding to a high energy condition, when a load current I.sub.L does not flow in the load feeder circuit, and gives an output signal I.sub.P of logic value "0" corresponding to a low energy condition, when a load current flows. For example the sensor 7 is constructed with a saturable magnetic body core. More specifically, a saturable magnetic body core which is respectively wound with an output lead of the current transformer 6, a primary winding for supplying an alternating current signal, and a secondary winding for receiving the signal. With this construction, when the load current I.sub.L flows in the load feeder circuit 3 of the load 2 so that a current flows in the output lead of the current transformer 6, the saturable magnetic body core becomes saturated. An alternating current signal supplied to the primary winding will therefore not be transmitted to the secondary winding side, and the output signal I.sub.P will not be produced (corresponding to logic value "0"). On the other hand, when the load current I.sub.L does not flow in the load feeder circuit 3 of the load 2 so that a current does not flow in the output lead of the current transformer 6, the saturable magnetic body core does not become saturated. An alternating current signal of the primary winding will therefore be transmitted to the secondary winding side, and the output signal I.sub.P produced (corresponding to logic value "1")
That is to say, the construction of the conventional load drive circuit is such that when a current does not flow to the load 2, or when the switch circuit 4 is switched on under normal conditions with input of the load drive signal I.sub.N, (i.e. when IP=1, or I.sub.N= 1), the electromagnetic relay 5 is excited so that the relay contacts 5A close.
For the excitation condition of the electromagnetic relay 5 of FIG. 9, the closed ("on") and open ("off") of the relay contacts 5A is represented by a binary signal "1" and "0" respectively, with the relay contacts 5A operating under the following conditions with respect to the load drive signal I.sub.N and the l
REFERENCES:
patent: 4384844 (1983-05-01), Yamamoto et al.
patent: 4394605 (1983-07-01), Terazawa
patent: 4661880 (1987-04-01), Futsuhara
patent: 4667184 (1987-05-01), Futsuhara
patent: 4933798 (1990-06-01), Widmayer et al.
patent: 5027114 (1991-06-01), Kawashima et al.
patent: 5341282 (1994-08-01), Brambilla et al.
patent: 5444595 (1995-08-01), Ishikawa et al.
"Realization of a Fail-Safe Train Wheel Sensor Using Electromagnetic Induction", by Koichi Futsuhara et al, IEEE Transactions on Instrumentation and Measurement, vol. 38, No. 2, Apr. 1989, pp. 421-427.
Futsuhara Koichi
Sakai Masayoshi
Shirai Toshihito
Paladini Albert W.
The Nippon Signal Co. Ltd.
Wysocki Jonathan
LandOfFree
Load drive circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Load drive circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Load drive circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-564969