How to Calculate Resistance Values for a Phototransistor Circuit?

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SUMMARY

This discussion focuses on calculating resistance values for a phototransistor circuit using the formula R = (V - Vf) / I. The key variables include supply voltage (V), LED voltage drop (Vf), and LED current (I), which can be sourced from the provided datasheets. Participants emphasized the importance of selecting a resistor that limits the current to a desired level for optimal circuit performance. The discussion highlights practical steps for applying these calculations effectively.

PREREQUISITES
  • Understanding of Ohm's Law and basic circuit theory
  • Familiarity with LED specifications and datasheets
  • Knowledge of phototransistor operation and characteristics
  • Experience with circuit design and analysis
NEXT STEPS
  • Research how to read and interpret LED datasheets
  • Learn about different resistor types and their applications in circuits
  • Explore the impact of varying supply voltage on LED performance
  • Investigate advanced circuit design techniques for phototransistor applications
USEFUL FOR

Electronics enthusiasts, circuit designers, and engineers involved in designing and optimizing phototransistor circuits will benefit from this discussion.

yaasir
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I need help to calculate the resistance values for the attached circuit diagram. I have also attached the data sheets. Can you help me.
 

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hi there yaasir
welcome to PF :)

for the IR LED (or any LED for that matter), choose a resistor that will limit the current (I) to a chosen value at an assumed Vf. And we have both of these.

R = (V - Vf) / I

R = the resistor
V = The supply voltage
Vf = the LED voltage drop
I = the LED current

Vf and I can be obtained from the datasheet you posted

see how you go :)

Dave
 

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