DD142098A1 - CIRCUIT ARRANGEMENT FOR PHOTOGRAPHIC CAMERAS - Google Patents

Description

Field of application of the invention

The invention relates to a circuit arrangement for photographic cameras for exposure control and display of exposure limits or of anticipated exposure values · _m '

Characteristic of the known technical solutions

It is known to use a common 'photoreceiver' for exposure control and display functions which is arranged in a current mirror circuit associated with a plurality of exposure control and display stages,

In these devices, the input of the film sensitivity and the compensation of larger tolerances of the Potoempfängers by incorporating other transistors in the measuring circuit takes place (WP 128 142) ·

Aim of the invention;

With the invention, devices of this type are to be improved ·

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presentation; the essence of the invention

The object of the invention is to provide a circuit arrangement with a common for control and display functions, not to be switched photo receiver, which on the one hand a higher accuracy, especially in the range of low Objektleuchtdichten, lower voltage and temperature dependence and a simple input of film sensitivities and correction values for the compensation of Photoreceiver tolerances ensured ·

According to the invention, this object is achieved in that. a differential amplifier or «operational amplifier is used, at the inverting input of the tap of a coupled with the Filmempfindlichkeitssteller one-positioner and the non-inverting input of the connection point of the series connection of the photoreceptor is connected to a transistor that the output of the amplifier based on the said transistor is fed back and base and emitter of the latter in a conventional manner with the same electrodes of other transistors, which are located in the inputs of switching stages for exposure control and exposure display connected. Said switching stages have constant threshold voltages so that the exposure time to be controlled and the display values become independent of the operating voltage.

Ausführunftsbeispiel

The invention will be explained with reference to an embodiment below

According to the circuit diagram shown, an adjusting controller 2 and are parallel to an operating voltage source 1 as well

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the series connection of a photoresistor 3 with a transistor 4 connected. The tap of the setting controller 2 is connected to the inverting input (-) of a differential amplifier 5, to whose non-inverting input (+) the connection point of the designated series circuit is fed. • The output of the differential amplifier 5 is fed back to the base of the transistor 4 and base and emitter the latter are connected to the same electrodes of further transistors 6, 7 and 8. The latter are located in the input of a respective threshold value switch 9 for exposure time control and threshold switches 10 or 11 with light emitting diodes 12, 13 for displaying exposure limits 15 a shutter operated switch and 16 denotes a holding magnet.

The mode of action is the following:

According to the sensitivity of the film in the camera is located at the tap of the setting controller 2 and thus on - input of the differential amplifier 5 is a fraction of the operating voltage U-g

^U 1 = ^a 1 · ^U B

The differential amplifier 5 controls the transistor 4 acting as a current source for the photoresistor so that the voltage U ₂ across the photoresistor 3 is equal to the partial voltage U _1. The current through the photoresistor thus has the value

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The current occurring at the output of the differential amplifier is impressed on the bases of all transistors 4, 6, 7, 8. By means of the common base-emitter voltage of all the transistors, their collector currents can be intentionally controlled in the same proportion to each other. The ratio of the individual collector currents is determined by the technological structure of the transistors and adapted to the requirements of the circuit »

After opening the switch 15 of the educational time ^is: charging capacitor 14 until reaching the Sehaltspannung U "of the threshold switch 9:

J_ f Ip. , dt C ) ^Ph

If the threshold voltage Uo is a multiple of the operating voltage U _ß . ,

U ₃ = a ₂ . U _B , _v follows the exposure time of the relationship

t = ^a 2 .Co Rp, φ (with constant "i7 ~ * ^ ObJktlhtdi

i7 object luminance)

The exposure time is thus independent of the operating voltage Ug. ,

As described above, the activation of the shift / value switches 10 and 11 takes place by means of the same 5 ¹ OtO resistor 5. For indicating whether the expected exposure time is above or below a certain limit value

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is located, the light emitting diodes 12, 13 are turned on via the threshold value switches.

The adjustment controller 2 can also be used to correct tolerances of the phototune receiver 3.

Instead of the photo resistor used in the embodiment, a photo element is used, which then has to be switched between the two inputs of the differential amplifier 5 _o

Claims (3)

210 545 claim for invention 1 · Circuit arrangement for photographic cameras with a common photoreceiver for exposure control and display of exposure limits or »expected exposure values, characterized in that a differential or operational amplifier (5) is used, at its inverting input of the tap of one coupled to the Pilmempfindlichkeitssteller Setting controller (2) and at the non-inverting input of the connection point of the series circuit of the photoreceptor (3) with a transistor (4) is connected, that the output of the amplifier is fed back to the base of said transistor and base and emitter d ^{- the} latter in at known manner with the same electrodes of other transistors (6, 7, 8), which are in inputs of switching stages (9, 10, 11,) for the exposure control and exposure display are connected. 2, circuit arrangement according to item 1, characterized in that the switching stages have constant threshold voltages. 3 «circuit arrangement according to item 1, characterized in that the phototransceiver is formed by a photoresistor of the transconductance T» Ao circuit arrangement according to item 1, gekannzeichnet in that the photoreceptor is formed by a closed between the inputs of the amplifier photoelement. For this purpose / f page, drawing.