THRESHOLD DETECTOR FOR INCIDENT RADIATION

• US 3,636,357 A
• Filed: 04/28/1970
• Issued: 01/18/1972
• Est. Priority Date: 05/09/1969
• Status: Expired due to Term

• Current Assignee: Giorgio Del Zotto
• Original Assignee: Giorgio Del Zotto
• Inventors: Del Zotto, Giorgio
• Primary Examiner(s): Stolwein, Walter
• Application Number:
  US05/032,658
• Time in Patent Office: 630 Days
• Field of Search: 250/210,214 315/159,158,149 307/311 317/124,130
• US Class Current: 250/210
• CPC Class Codes: H01H 47/24 having light-sensitive input
• CPC Class Codes: H03K 17/941 using an optical detector H03K17/968 takes precedence

Abstract

A resistance bridge, having one diagonal connected across a source of direct current, includes in its other diagonal the base/emitter circuit of an input transistor controlling a switching transistor of the opposite conductivity-type. The latter transistor controls a relay which operates when a photoresistor in one of the arms of the bridge is illuminated; a regenerative feedback connection from the output of the switching transistor exerts a toggle effect by modifying the bias of the input transistor to vary the sensitivity of the detector in a sense tending to maintain the relay in either its operated or its unoperated state.

Claims

1. A circuit arrangement for detecting incident radiation, comprising a source of direct current;

a resistance bridge having one diagonal connected across said source;

a radiation-sensitive resistance element and resistance means serially connected in an arm of said bridge;

a signal amplifier having an input connected across the other diagonal of said bridge;

a load circuit including relay means connected to the output of said amplifier for alternate energization and deenergization in response to variations in the level of radiation incident upon said resistance element; and

regenerative feedback path constituted by a conductive connection extending from said output to a junction between said resistance means and said resistance element.

2. A circuit arrangement as defined in claim 1 wherein said feedback path includes an adjustable resistor.

3. A circuit arrangement as defined in claim 1 wherein said relay means has a winding in series with a pair of output electrodes of said amplifier, said feedback path originating at a junction of one of said output electrodes with said winding. 4. A circuit arrangement as defined in claim 3 wherein said amplifier comprises a first transistor stage of one conductivity type and a second transistor stage of opposite conductivity type, said one of said output electrodes being a collector of said second stage.

5. A circuit arrangement as defined in claim 4 wherein said first stage has an emitter connected to a junction of two other arms of said bridge, one of said other arms including an adjustable resistor.

6. A circuit arrangement as defined in claim 4 wherein said load circuit forms a resistive connection including said winding between said collector and a terminal of said source, the resistance of said resistive connection being high compared with that of said resistance means.