Automatic power control for modulated LED photoelectric devices

• US 4,598,198 A
• Filed: 05/21/1984
• Issued: 07/01/1986
• Est. Priority Date: 05/21/1984
• Status: Expired due to Term

• Current Assignee: Banner Engineering Corporation
• Original Assignee: Banner Engineering Corporation
• Inventors: Fayfield, Robert W.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Allen, Stephone B.
• Application Number:
  US06/612,664
• Time in Patent Office: 771 Days
• Field of Search: 250/205, 250/206, 250/214, 250/214 C, 250/214 DC, 250/552, 307/311, 315/149, 315/154, 315/156, 315/158, 315/307
• US Class Current: 250/205
• CPC Class Codes: H05B 45/305 Frequency-control circuits
• CPC Class Codes: H05B 45/32 Pulse-control circuits
• CPC Class Codes: H05B 45/395 Linear regulators

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.

Claims

1. A modulated light source for a photoelectric control, comprising:

means for providing a variable frequency, variable duty cycle pulsed modulating signal;

a light emitting diode;

a power source for supplying electrical energy to said light emitting diode;

means operatively connected for selectively causing said light emitting diode to conduct current from said power source in response to said pulsed modulating signal; and

means for providing electrical energy to said power source at a controlled rate such that the power supplied to said light emitting diode from said power source on each pulse varies approximately inversely with changes in the duty cycle of the pulsed modulating signal, thereby maintaining the average power of the light emitting diode relatively constant.

2. A modulated light source for a photoelectric control, comprising:

means for providing a variable frequency, variable duty cycle pulsed modulating signal;

light emitting diode;

a power source including a capacitor connected to supply operating potential for said light emitting diode;

means operatively connected for selectively causing said light emitting diode to conduct, current from said capacitor in response to said pulsed modulating signal; and

means for providing controlled charging of said capacitor such that the charge of the capacitor varies approximately inversely with changes in the duty cycle of the pulsed modulating signal, thereby maintaining the average power of the light emitting diode relatively constant.

3. A modulated light source according to claim 2 wherein said variable pulsed modulating signal consists of variable frequency, variable duty cycle pulses having a constant pulse duration.

4. A modulated light source according to claim 2 wherein said means for providing controlled charging of said capacitor comprises a further power supply, and an impedance connected for supplying current from said further power supply to said capacitor.

5. A modulated light source according to claim 2 wherein said means for selectively causing said light emitting diode to conduct comprises a switching element in series connection with said light emitting diode and said capacitor without a load impedance for said light emitting diode.

6. A modulated light source according to claim 2 wherein said capacitor discharges only a small percentage of its charge on each pulse.

7. A modulated light source for a photoelectric control, comprising:

means for providing a pulsed modulating signal which can be varied in frequency and also in duty cycle;

a light emitting diode;

a capacitor for supplying operating potential for said light emitting diode;

switching means and means connecting said switching means in series circuit with said light emitting diode and said capacitor, said switching means operative in response to said pulsed modulating signal to cause said light emitting diode to conduct current from said capacitor and thereby emit corresponding pulses of light; and

means including an impedance connected for providing recharging current to said capacitor so that the average charge of the capacitor decreases with increases in the duty cycle of the pulsed modulating signal and vice versa to maintain the average power of the light emitting diode relatively constant as the frequency and duty cycle of the modulating signal are changed.

8. A modulated light source for a photoelectric control, comprising:

signal means for providing a variable frequency, variable duty cycle pulsed modulating signal;

a power source for providing operating potential to said signal means;

a light emitting diode;

a capacitor for supplying operating potential to said light emitting diode;

switching means connected in series circuit with said light emitting diode and said capacitor, and responsive to pulses of said modulating signal to cause said light emitting diode to conduct current from said capacitor and to emit corresponding pulses of light; and

an impedance connected for providing recharging current from said power source to said capacitor at a controlled rate such that the power supplied by said capacitor to said light emitting diode on each pulse varies approximately inversely with changes in the duty cycle of the pulsed modulating signal, thereby maintaining the average power of the light emitting diode relatively constant.