| 摘要 |
For an electrical circuit 10, having a load 20 such as an illuminated display that includes at least one semiconductor junction device 22 supplied with operating current at a voltage sufficient to bias the semiconductor junction device into conduction and a controller 30 to provide or inhibit supply of power to said load, there is provided a protection arrangement 40 including sensor circuitry 50 for sensing characteristics of the load when it is off-line, that is, when the operating current is not flowing. The sensing circuitry is coupled to the load where and when supplied with operating power and operable in the absence of such supply to sense a voltage level across the load. Threshold comparator 54 compares the sensed voltage level with at least one stored value representative of a threshold of a load characteristic delimiting consistency with semiconductor and non-semiconductor behaviour. The supply of operating current to the load is interrupted periodically for a time interval too short to be noticed, and the sensing circuitry includes a sensing current generator 62 which in the absence of operating current to the load effects passage through the load of a sensing current having a value that is less, for a semiconductor junction, than the forward conduction threshold thereof. The voltage level across the load in response to this sensing current is sensed, and threshold comparison determines if the sensed voltage level is below a value, predetermined as the minimum for said sensing current consistent with a semiconductor junction and maximum for the load having conduction characteristics from which the circuit requires protection from the application of said operating power, and the controller responds to the absence of such condition to establish or re-establish operating current to the load and to the existence of such condition to keep the load unpowered. The voltage behaviour may be used to sense other load characteristics, such as capacitance that may be due to an introduced liquid, in any interval when the load is taken off-line.
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