This photo IC was developed to detect the beam passage timing of the write laser used for laser printers and digital copiers, etc. It contains a high-speed photodiode and high-speed signal processing circuit to provide stable detection timing.
The analog amplitude (voltage change generated by passage of laser beam) at the Ro terminal is expressed as Vro＝Current gain x Photosensitivity x External gain resistance. External gain resistance is selected so that Vro is set to 2 to 3 V (resistance is selected in a range from 1 to 10 kilohms). Current gains of 4, 6, and 20 times are provided and selectable to match the laser beam power. In the case of dual-element type, use a resistor of the same resistance for connection to Ro1 and Ro2.
Visible light cutoff type is sensitive to light at a wavelength from 700 to 1100 nm (peak sensitivity wavelength: 850 nm), so an LED that emits light at 800 to 950 nm is recommended. Transparent plastic package type has sensitivity in the 400 to 1100 nm range (peak sensitivity wavelength: 800 nm), so an LED in the visible to infrared range would be suitable.
Single-element types can be scanned in either left or right direction, but dual-element types should be scanned in the direction from Ch 1 to Ch 2.
To utilize an advantage offered by dual-element types, which is timing stability versus power and temperature fluctuations, the Ro1 and Ro2 terminal voltage waveforms must form a cross (X) shape at the center of the dual-element photodiode. As a calculated figure, the analog amplitude that can be obtained as output is 1.5 to 8 V. However, setting the analog amplitude too high may cause faulty operation due to stray light inside the package (stray light occurring at about 6% of the ΔVRo). Setting the upper limit somewhat larger than 3 V (up to about 6 V) will not cause problems, but an excessively large analog amplitude may make it difficult to obtain a stable output, so up to 3 V is recommended.
An amplitude level greater than or equal to 1.5 V will not cause problems. However, a level below 1.5 V will prevent obtaining a cross waveform from the gain resistance terminals, so the output will no longer be stable during power and temperature fluctuations.
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