| 摘要 |
A sensor circuit for detecting the occurrence of welding is disclosed. The sensor circuit uses a phototransistor operative to receive a light input and produce an output representative thereof. A resistor is coupled between the phototransistor's base and emitter to control the phototransistor's response to low intensity and high intensity light. An amplifier may be coupled to the output of the phototransistor so as to provide a gain for the output of the phototransistor; and feedback means may coupled to the phototransistor to bias the phototransistor, the feedback means comprising a resistor capacitor circuit for following the output of the phototransistor, a feedback transistor to provide a feedback signal to the phototransistor, and a resistor coupled between the base and the emitter of the phototransistor. Preferably the phototransistor is a planar phototransistor having a surface mount. The sensor circuit may also be used in an auto-darkening eye protection device, such as a welding helmet or the like, that delivers a drive signal to a shutter assembly upon the detection of welding, the drive signal being operative to drive the shutter assembly to a darkened, protective state. A solar cell may be used to reduce the circuit's power consumption by powering various circuit components only when the welding helmet is exposed to light. The present invention provides reduced power consumption, improved attenuation of low intensity light signals, a sharp rise time from the phototransistor in response to high intensity light, and allows implementation into a smaller sleeker eye protection device.
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