Automatic power control for modulated LED photoelectric devices
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United States of America Patent
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Jul 1, 1986
Grant Date -
N/A
app pub date -
May 21, 1984
filing date -
May 21, 1984
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A pulsed light emitting diode used as the light source in a photoelectric scanner is operated from a secondary power source which automatically adjusts the power to the LED approximately inversely proportional to frequency as the modulating frequency of the scanner is adjusted over a range, so that the average power of the LED remains approximately constant, within safe operating limits and close to optimum, over the range of adjustment. In the preferred embodiment this is accomplished by operating the LED from a capacitor used as a secondary power source without a series current limiting resistor for the LED. Peak current is determined by the forward characteristics of the diode and the voltage on the capacitor, and an impedance controls the recharging of the capacitor during the off time such that the desired average power characteristics are achieved as operating frequency varies.
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