What is the difference in usage between a phototransistor output and a photo IC output?


What is the difference in usage between a phototransistor output and a photo IC output for Photomicrosensors (photointerrupters)?



With a phototransistor output, the threshold level to activate the switch is adjusted using an external circuit, whereas with photo IC output, the threshold level is fixed at an internal circuit board. Phototransistor outputs enable users to set an optimum threshold level according to the application. Photo IC output is ideal for applications requiring a fast response time.



The following chart explains the difference between phototransistor output and photo IC output. Please use this as a guide when selecting your sensor and check the specification datasheet for product details.


Quick tips

The photo IC output type (3 kHZ and above) is recommended for applications that require a sensor with a fast response time, such as for counting RPMs on high-speed rotating disk. With the phototransistor output type, the load resistance is set from the expected lower limit of the light current (IL). Note that the larger the resistance value, the slower the response becomes. Please refer to the “Response time - Load Resistance Characteristics.” With the photo IC output type, there is no need to consider this point, which is an advantage for easy design, but note that it takes 100 ms for the IC to stabilize after power activation. If the equipment is designed to turn the power OFF when not in use (energy-saving design), make sure that the output reading is adjusted to avoid within the 100 ms time.


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