Automatic power control for modulated LED photoelectric devices
US4598198A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | May 21, 1984 |
| Grant date | Jul 1, 1986 |
| Priority date | — |
| Expiry date | May 21, 2004 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH05B45/395
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.