Calculating R1 and R2 for Opto-Triac Output Circuit

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SUMMARY

The forum discussion focuses on calculating the resistor values R1 and R2 for an opto-triac output circuit with a logic voltage of 3.3 V, a forward voltage drop of 1.8 V for diode D1, and a minimum operating current of 2 mA for the opto-triac. The calculations reveal that R1 should be 150 Ω and R2 should be 20 Ω to ensure proper current flow through the circuit. The discussion emphasizes the importance of understanding the circuit configuration, particularly the distinction between series and parallel arrangements, to avoid miscalculations.

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  • #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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