Patent Application
20100328828
This application relates to circuit protection, and more particularly to a method of providing circuit protection while avoiding nuisance tripping.
Previous circuit protection methods, such as a standard fuse or circuit breaker, simply interrupt a current once it exceeds a threshold (e.g. a current threshold). Fuses, for example, have a slow response time, during which damage to a load may occur. Also, transient currents can exceed such thresholds for brief periods of time, causing nuisance current interruptions.
A method of protecting a circuit includes measuring a value associated with a circuit having a current flowing through a switch to a load and comparing the measured value to a threshold. If the measured value meets or exceeds the threshold, the switch is turned OFF and a counter is incremented. If the counter is less than the counter limit, and a predefined time period has elapsed, the switch is turned back ON.
A protection circuit includes a power source, a load, a switch operable to control a flow of current from the power source to the load. A detection circuit is operable to measure a value associated with the protection circuit, and is operable to compare the measured value to a threshold. A switch controller is operable to turn the switch ON or OFF. If the measured value meets or exceeds the threshold, the switch controller turns the switch OFF and increments a counter. If the counter is less than a counter limit, and a predefined time period elapses, the switch controller turns the switch ON.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
Referring to
If the counter 22 exceeds a counter limit (step 110), the switch controller 20 leaves the switch 16 OFF and indicates a service condition (step 112). In one example, indicating a service condition includes notifying an individual that the power source 12 or the load 14 needs inspection.
If the counter 22 is less than the counter limit (step 110), the timer 24 is started. Once a predefined time period associated with the timer 24 has elapsed, the switch 16 is turned ON (step 114) and the timer 24 is reset. In one example the time period is on the order of 5-50 mini seconds. Once the switch 16 is turned back ON, steps 104-114 may then be selectively repeated while protection is desired.
In one example, the switch controller 20 turns the switch 16 OFF or ON to protect the switch 16, not to protect the load 14, detection circuit 18, or switch controller 20.
The value associated with the circuit 10 could correspond to a number of different conditions for which it is desirable to provide protection. In one example the measured value is an electrical current flowing through the switch 16 to the load 14, and the threshold is a current threshold. In one example the measured value is a temperature of the protection circuit 10, and the threshold is a temperature threshold. In one example the measured value is an amount of energy flowing from the power source 12 to the load 14, the threshold is an energy threshold, and the processing unit 26 is operable to calculate energy using equations #1, #2 below.
W=V*I equation #1
where W is wattage;
E=V*I*t equation #2
where E is an amount of energy; and
The method 100 enables successful detection of damaging conditions (e.g. high current spikes, high temperatures, etc.) in the circuit 10 to effectively protect the circuit 10, while at the same time preventing nuisance tripping resulting from non-damaging conditions (e.g. high current spikes resulting from in-rush current, noise, electromagnetic interference, etc.). Nuisance tripping is avoided by the retrial approach (steps 108-114), since non-damaging conditions normally have a short time duration.
In one example, the opening of switch 16 (step 108) and subsequent closing of the switch 16 (step 114) happens quickly enough (e.g. on the order of 1-20 mini seconds) that if the load 14 is a lighting load the human eye would not detect the load 14 having been turned OFF. Thus, in this example the human eye would be unable to detect a single OFF/ON period for the switch 16, or multiple OFF/ON periods (i.e. step 104, 108, 110, 114 repeated several times consecutively).
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
