| 摘要 |
A two-terminal overcurrent sensing transistor circuit of the fold-back type is inserted in electrical series relationship with an AC load and an associated load-energizing, solid state, semiconductor switch. Under normal operating conditions, the transistor circuit presents a very low impedance to permit load energization when the solid state switch is conducting, and hence has a very low impedance. Upon sensing an overcurrent condition, caused for example by a short circuit across the load, the transistor circuit rapidly switches to and locks into a high impedance circuit protection state to limit current through the series-associated solid state switch. A charged capacitor holds the transistor circuit into its high impedance state subsequent to clearing of the short circuit fault until reset by interrupting the application of power to it. The disclosed protection scheme finds particularly advantageous use in the short circuit protection of AC line-operated proximity switches. The foregoing abstract is merely a resume of one general application, is not a complete discussion of all principles of operation or applications, and is not to be construed as a limitation on the scope of the claimed subject matter.
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