Light sensor with false quench inhibit circuit and temperature compensation

Claim 2

For use with an electronic flash unit, a light sensing means comprising; terminal means for connection to a source of supply voltage; threshold signal means connected to said terminal means for providing a threshold signal derived from said supply voltage; light responsive means for providing a light controlled signal in response to light received thereby; integrating means connected to said light responsive means for providing a light integral signal representative of the integral of the light received by said light responsive means; switching means connected to said threshold signal means and said integrating means for providing an effective contact closure whenever the magnitude of said light integral signal exceeds the magnitude of said threshold signal, said eFfective contact closure being operable to initiate a quench of the flash unit; and voltage responsive means connected to said threshold signal means, said voltage responsive means being responsive to predetermined changes in said supply voltage, for effectively preventing said changes from adversely affecting the magnitude of said threshold signal whereby to effectively prevent a false quenching of said flash unit which might otherwise result from said changes in said supply voltage.

Claim 3

The light sensing means as set forth in claim 1 wherein said changes in said supply voltage are decreases in said supply voltage, said voltage responsive means including switching means responsive to said decreases in said supply voltage for effectively disconnecting said threshold signal means from said terminal means.

Claim 4

The light sensing means as set forth in claim 1 wherein said light sensing means includes: first and second input terminals of said terminal means for connection to said flash unit from whence said supply voltage is furnished, said switching means comprising a light activated silicon controlled rectifier (LASCR) having anode cathode and gate terminals, said light responsive means being a light responsive junction of said LASCR, said LASCR anode terminal being connected to said first input terminal, said integrating means comprising a capacitor connected between said LASCR gate terminal and said second input terminal, said threshold signal means and said voltage responsive means comprising a voltage divider having a first, second and pick-off terminals thereon, said voltage divider first terminal being connected to said LASCR anode terminal, a storage means connecting said LASCR cathode terminal with said second input terminal, a voltage responsive device having first and second terminals, said first terminal of said voltage responsive device being connected to said LASCR anode terminal, a second switching means having first, second, and control terminals, said first terminal of said second switching means being connected to said second terminal of said voltage divider means, said second terminal of said second switching means being connected to said second input terminal, said control terminal of said second switching means being connected to said second terminal of said voltage responsive device, and impedence means connected between said anode terminal of said LASCR and said second input terminal.

Claim 5

For use with an electronic flash unit, a light sensing means comprising: terminal means for connection to a source of supply voltage; a threshold signal circuit connected to said terminal means for providing a threshold signal derived from said supply voltage; light responsive means for providing a light controlled signal in response to the intensity of light received thereby, said light responsive means being affected by ambient temperature to modify the magnitude of said light controlled signal in variable accordance therewith; integrating means connected to said light responsive means for providing a light integral signal representative of the integral of the light received by said light responsive means; switching means connected to said threshold signal circuit and said integrating means for providing an effective contact closure whenever the magnitude of said light integral signal exceeds the magnitude of said threshold signal, said effective contact closure being operable to quench the flash unit; and temperature compensation means in said threshold signal circuit, said temperature compensation means being in thermal proximaty to said light responsive means, said temperature compensation means being operative to modify said threshold signal in variable accordance with said ambient temperature in a manner to offset the influence of ambient temperature on said light responsive means whereby the time magnitude interrelationship between said threshold signal and said integral signal is substantially uNaffected by ambient temperature.

Claim 6

For use with an electronic flash unit, a light sensing means comprising: terminal means for connection to a source of supply voltage; a threshold signal circuit connected to said terminal means for providing a threshold signal derived from said supply voltage; light responsive means for providing a light controlled signal in response to the intensity of light received thereby, said light responsive means being affected by ambient temperature to modify the magnitude of said light controlled signal in variable accordance therewith; integrating means connected to said light responsive means for providing a light integral signal representative of the integral of the light received by said light responsive means; switching means connected to said threshold signal circuit and said integrating means for providing an effective contact closure whenever the magnitude of said light integral signal exceeds the magnitude of said threshold signal, said effective contact closure being operable to quench the flash unit; and temperature compensation means in said threshold signal circuit, said temperature compensation means being in thermal proximaty to said light responsive means, said temperature compensation means being operative to modify said threshold signal in variable accordance with said ambient temperature in a manner to offset the influence of ambient temperature on said light responsive means whereby the time magnitude interrelationship between said threshold signal and said integral signal is substantially uNaffected by ambient temperature.

Claim 7

The light sensing means as set forth in claim 4 including: first and second input terminals of said terminal means for connection to the flash unit from whence said supply voltage is furnished, said switching means comprising a light activated silicon controlled rectifier (LASCR) having anode, cathode, and gate terminals, said light responsive means being a light responsive junction of said LASCR, said LASCR anode terminal being connected to said first input terminal, said integrating means comprising a capacitor connected between said LASCR gate terminal and said second input terminal, said threshold signal circuit comprising said temperature compensation means having first and second terminals thereof, said first terminal of said temperature compensation means being connected to said LASCR anode terminal, voltage divider means having first, second and pickoff terminals thereof, said first and second terminals of said voltage divider means being connected to said second terminal of said temperature compensation means and said second input terminal, respectively, storage means connected between said LASCR cathode terminal and said second input terminal, said pick-off terminal being connected to said LASCR cathode terminal, said temperature compensation means being responsive to changes in ambient temperature for inversely changing the magnitude of its electrical impedence.

Claim 8

The light sensing means as set forth in claim 5 wherein said temperature compensation means is a temperature responsive resistor.

Claim 9

The light sensing means as set forth in claim 4 wherein said light sensing means further includes voltage responsive switching means connected to said threshold signal circuit, said voltage responsive means being responsive to predetermined changes in said supply voltage for effectively preventing said changes from adversely affecting the magnitude of said threshold signal whereby to effectively prevent a false quenching of said flash unit which might otherwise result from said changes in said supply voltage.

Claim 10

The light sensing means as set forth in claim 5 characterized by the addition of a second switching means serially connected between said second terminal of said voltage divider means and said second input terminal, said second switching means further having a control terminal, voltage responsive switching device having first and second terminals, said first terminal of said voltage responsive switching device being connected to said LASCR anode terminal, said second terminal of said voltage responsive switching device being connected to said control terminal of said second switching means, and impedence means connected between said LASCR anode terminal and said second input terminal.