Calculating R1 and R2 for Opto-Triac Output Circuit

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The discussion focuses on calculating the resistor values R1 and R2 for an opto-triac output circuit, given specific parameters such as logic voltage and forward voltage drops. Participants express confusion about whether the circuit is in series or parallel, leading to different calculations for the resistors. The consensus is that R1 should be 150 Ω and R2 should be 850 Ω, with R2 designed to reduce the current to the opto-triac's minimum operating current of 2 mA. The importance of understanding the circuit diagram and current flow direction is emphasized for accurate calculations. Ultimately, the conversation highlights the need for careful analysis of circuit configurations to determine appropriate resistor values.
  • #31
Here's the diagram with calculations:

LED.PNG
 
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  • #32
As suspected, it's a different arrangement.
 
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  • #33
R1 = 150 Ω
R2 = 850 Ω

This question was easier than the example question.

It is important to read and understand the diagram before throwing things onto the page in panic.
 
  • #34
Michael Neo said:
What do you mean by "... you'll choose one of the preferred values"?
If you go into a city electronics store and ask for an 850 ohm resistor, the salesperson will say, "Sorry, but no one stocks that value."
 
  • #35
Thank you for the excellent advice and support, NascentOxygen.
 

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