| 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) suppli ed with operating current at a voltage sufficient to bias the semiconductor junction device into conduction and control means (30) to provide or inhibit supply of power to said load, there is provided a protection arrangement (40 ) comprising means (50) for sensing characteristics of the load when it is off - line, that is, when the operating current is not flowing. The sensing means is coupled to the load where and when supplied with operating power and operabl e in the absence of such supply sense a voltage level across the load. Thresho ld comparison means (54) compares the sensed voltage level with at least one stored value representative of a threshold of a load characteristic delimiti ng consistency with semiconductor and non-semiconductor behaviour. In a preferr ed embodiment the supply of operating current to the load is interrupted periodically for a time interval too short to be noticed, the sensing means including 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 conductionthreshold thereof. The voltage level across the load in response t o 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 control mea ns 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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