Calculating R1 and R2 for Opto-Triac Output Circuit

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Discussion Overview

The discussion revolves around calculating the resistor values R1 and R2 for an opto-triac output circuit, focusing on the implications of circuit configuration (series vs. parallel) and the associated current requirements for the components involved. Participants explore the relationships between voltage, current, and resistance within the context of this circuit design.

Discussion Character

  • Homework-related
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant calculates R1 and R2 based on the assumption of a parallel circuit, leading to a series of equations involving Ohm's law and voltage drops.
  • Another participant suggests treating each parallel path as a series circuit to simplify calculations, prompting further exploration of the circuit's configuration.
  • Multiple participants express confusion regarding whether the circuit is series or parallel, with some asserting that the current splits in a parallel configuration while others argue for a series interpretation.
  • Discussions arise about the minimum operating current for the opto-triac and how it affects the design of R2, with varying interpretations of how to calculate the necessary resistance values.
  • Some participants propose different values for R1 and R2 based on their interpretations of the circuit and the current flowing through each component.
  • There is a suggestion that designing for a higher current than the minimum may be more reliable, indicating a preference for practical design considerations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the circuit is best understood as a series or parallel configuration, leading to multiple competing views on the calculations for R1 and R2. There is also disagreement on the appropriate current values to use for these calculations.

Contextual Notes

Participants express uncertainty regarding the implications of the circuit configuration on current flow and resistance calculations. There are unresolved assumptions about the definitions of operating and minimum currents, as well as the impact of the diode's forward voltage drops on the overall circuit behavior.

  • #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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