Pulsed light barrier apparatus for direct connection to an a.c.

Details Pulsed light barrier apparatus for direct connection to an a.c. Pulsed light barrier apparatus for direct connection to an a.c.

1982-03-19

1984-12-04

Westin, Edward P.

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

250221, 307252B, 307311, H01J 4014

Patent

active

044866569

ABSTRACT:
Pulsed light barrier apparatus is driven directly from an a.c. supply voltage connected to the terminals L and M with the terminal M being earthed. A storage capacitor 14 is charged during the positive half wave of the a.c. supply voltage and is discharged at a time determined by a programmable unijunction transistor 13 through a photodiode 11 to emit a flash of light which passes across a region monitored by the light barrier to a photoreceiver 26. A Zener diode limits the voltage across the storage capacitor 14 to a value less than the peak a.c. supply voltage. As soon as the voltage across the storage capacitor has reached the Zener breakdown voltage the excess energy from the a.c. supply voltage is directed through a rectifier diode 18 to a smoothing capacitor 19 where it forms a positive operating voltage for the light receiver arrangement. During the negative half wave of the a.c. supply voltage the electrical energy is supplied via a further rectifier diode 20 connected in the opposite direction to the rectifier diode 18 to a further smoothing capacitor 21 where it forms the negative operating voltage for the light receiver arrangement. The circuitry described prevents high initial currents on switching on the device, results in suppression of noise voltages, minimizes power losses and can be connected to a wide variety of control circuits without special interfaces.

REFERENCES:
patent: 3723737 (1973-03-01), Zeldman et al.
patent: 3889118 (1975-06-01), Walker
patent: 4119905 (1978-10-01), Head

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