PHOTOELECTRIC DETECTORS 



The spectral response of the P50A is shown in Figure 28.49. It can be seen 

 that the response fits well the spectral output of a tungsten source, so that 

 good transfer of energy from source to detector may be expected. 



m 2A 



^ 22 



20 



^ 18 



f 16 



° 1^ 

 § 12 

 10 

 8 

 6 

 4 

 2 





 -2 



u 



> 





0-5 07 0-9 



11 13 15 

 Wavelengh 



1-7 1-9 



21 



microns 



Figure 28.49 Spectral response curve of a typical P50A Standard Telephones 

 and Cables germanium diffusion-junction photodetector 



AGO 600 800 1,000 1,200 1^400 1,600 

 Current through cell uA 



Figure 28.50 Performance data of an average P50A germanium phototransistor 



The cell must be used with an electrical power source of the correct 

 polarity. Figure 28.50 shows the current versus applied voltage characteris- 

 tics for an average cell at various light levels at a temperature of 20°C. At 

 least 1 V must be applied before the cell will function. The effect of a 100 

 kilohm load is also shown. Due to the small area of the active photosensitive 

 element (0- 1 5 mm^) the sensitivity of the device to unfocused illumination is 



379 



