Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Converting – per se – of an ac input to corresponding dc at an...
Reexamination Certificate
1999-04-28
2001-06-26
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Converting, per se, of an ac input to corresponding dc at an...
C327S330000
Reexamination Certificate
active
06252439
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally concerned with protecting a circuit of any kind against overcurrents such as those caused by a short circuit, for example.
It is more particularly directed to the situation in which instead of using a fuse of any kind to provide this protection, in the conventional way, where the fuse must be changed each time it operates, the current is read, or to be more precise, the current level is detected, for appropriate intervention in the circuit to be protected as soon as the current level reaches a particular threshold.
2. Description of the Prior Art
The current level detector devices usually employed use resistor means inserted into the circuit to be protected and serving as a sensor and a detector cell shunting the resistor means.
In alternating current circuits there are two feasible solutions.
A first solution uses only one detector cell and rectification with no threshold is therefore employed.
However, this solution has the disadvantage of requiring considerable and costly post-processing of the information collected.
A second solution uses two detector cells, one for each half-wave of the current, and each of the two detector cells is connected to specific resistor means in a mirror type circuit.
This has the advantage of simplifying the required processing of the information collected.
In practice the two detector cells employed are similar and each has two inputs connected to the corresponding resistor means.
The resistor means can in some cases be a low value resistor and in this case heat dissipation within the resistor advantageously remains moderate.
This is not always the case, however, especially if the associated detector cell uses a selectively operable switch, for example a transistor, which is triggered by applying a sufficient potential to its base circuit.
Heat dissipation in the resistor means can remain acceptable if the power in the circuit to be protected remains moderate, however.
This is not the case for higher powers, for example if the circuit to be protected uses power semiconductors.
A general aim of the present invention is an arrangement providing a very simple and effective way to reduce heat dissipation in this case, and which also has other advantages.
SUMMARY OF THE INVENTION
To be more precise, the present invention consists in a current level detector device for protecting a circuit against alternating current overcurrents, including resistor means adapted to be inserted into the circuit to be protected and two similar detector cells, one for each half-wave of the current, connected to the resistor means at first and second inputs, wherein the two detector cells are both connected by a crossover circuit to first and second terminals of the same resistor means, one of the central cells is connected to the first terminal at its first input and to the second terminal at its second input and the other detector cell is connected to the first terminal at its second input and to the second terminal at its first input.
Briefly, in accordance with the invention the resistor means employed are advantageously operative in both current directions, without any rectification.
Accordingly, although the resistor means retain the value necessary for the required detection to be assured on each half-wave, it is advantageously possible to halve their value overall.
This reduces heat dissipation commensurately.
The cost and the overall size of the system are also reduced, which is advantageous.
The features and advantages of the invention will emerge from the following description given by way of example with reference to the accompanying diagrammatic drawings.
REFERENCES:
patent: 3743919 (1973-07-01), Bingley
patent: 5315651 (1994-05-01), Rahamim et al.
patent: 5864458 (1999-01-01), Duffy et al.
patent: 1538286 (1970-02-01), None
patent: 2279189 (1994-12-01), None
Lam Tuan T.
Legrand
Nguyen Hiep
Young & Thompson
LandOfFree
Current level detector device for protecting a 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 Current level detector device for protecting a circuit..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Current level detector device for protecting a circuit... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2484376